INTERNATIONAL PROGRAMME ON CHEMICAL SAFETY
ENVIRONMENTAL HEALTH CRITERIA 179
Morpholine
This report contains the collective views of an international group of
experts and does not necessarily represent the decisions or the stated
policy of the United Nations Environment Programme, the International
Labour Organisation, or the World Health Organization.
First draft prepared by Dr. J. Kielhorn and Dr. G. Rosner, Fraunhofer
Institute of Toxicology and Aerosol Research, Hanover, Germany
Published under the joint sponsorship of the United Nations
Environment Programme, the International Labour Organisation, and the
World Health Organization
World Health Organization
Geneva, 1996
The International Programme on Chemical Safety (IPCS) is a joint
venture of the United Nations Environment Programme, the International
Labour Organisation, and the World Health Organization. The main
objective of the IPCS is to carry out and disseminate evaluations of
the effects of chemicals on human health and the quality of the
environment. Supporting activities include the development of
epidemiological, experimental laboratory, and risk-assessment methods
that could produce internationally comparable results, and the
development of manpower in the field of toxicology. Other activities
carried out by the IPCS include the development of know-how for coping
with chemical accidents, coordination of laboratory testing and
epidemiological studies, and promotion of research on the mechanisms
of the biological action of chemicals.
WHO Library Cataloguing in Publication Data
Morpholine.
(Environmental health criteria ; 179)
1.Morpholine 2.Solvents 3.Chemical industry
4.Environmental exposure I.Series
ISBN 92 4 157179 9 (NLM Classification: TP 247.5)
ISSN 0250-863X
The World Health Organization welcomes requests for permission to
reproduce or translate its publications, in part or in full.
Applications and enquiries should be addressed to the Office of
Publications, World Health Organization, Geneva, Switzerland, which
will be glad to provide the latest information on any changes made to
the text, plans for new editions, and reprints and translations
already available.
(c) World Health Organization 1996
Publications of the World Health Organization enjoy copyright
protection in accordance with the provisions of Protocol 2 of the
Universal Copyright Convention. All rights reserved. The designations
employed and the presentation of the material in this publication do
not imply the expression of any opinion whatsoever on the part of the
Secretariat of the World Health Organization concerning the legal
status of any country, territory, city or area or of its authorities,
or concerning the delimitation of its frontiers or boundaries. The
mention of specific companies or of certain manufacturers' products
does not imply that they are endorsed or recommended by the World
Health Organization in preference to others of a similar nature that
are not mentioned. Errors and omissions excepted, the names of
proprietary products are distinguished by initial capital letters.
CONTENTS
ENVIRONMENTAL HEALTH CRITERIA FOR MORPHOLINE
1. SUMMARY AND EVALUATION, CONCLUSIONS AND RECOMMENDATIONS
1.1. Physical and chemical properties
1.2. Analytical methods
1.3. Sources of human and environmental exposure
1.4. Environmental transport, distribution and transformation
1.5. Environmental levels and human exposure
1.6. Kinetics and metabolism in laboratory animals and humans
1.7. Effects on laboratory mammals and in vitro test systems
1.8. Effects on humans
1.9. Effects on other organisms in the laboratory and field
1.10. Evaluation of human health risks and effects on the
environment
1.10.1. Evaluation of effects on human health
1.10.2. Evaluation of effects on the environment
1.11. Conclusions and recommendations
1.11.1. Recommendations for protection of human health
1.11.2. Recommendations for protection of the environment
1.11.3. Recommendations for further research
2. IDENTITY, PHYSICAL AND CHEMICAL PROPERTIES, AND ANALYTICAL
METHODS
2.1. Identity
2.1.1. Technical product
2.1.2. Impurities
2.2. Physical and chemical properties
2.2.1. Physical properties of morpholine
2.2.1.1 Storage of morpholine
2.2.2. Chemical properties of morpholine
2.3. Conversion factors for morpholine
2.4. Analytical methods
2.4.1. Determination of morpholine in air
2.4.2. Determination of morpholine in water
2.4.3. Determination of morpholine in soil and sediments
2.4.4. Determination in biological and other material
3. SOURCES OF HUMAN AND ENVIRONMENTAL EXPOSURE
3.1. Natural occurrence
3.2. Anthropogenic sources
3.2.1. Production levels and processes
3.2.1.1 World producers
3.2.1.2 Production figures
3.2.1.3 Production processes
3.2.1.4 Losses to the environment during normal
production
3.2.1.5 Methods of transport
3.2.1.6 Accidental release
3.2.2. Uses
3.2.2.1 Rubber chemicals
3.2.2.2 Anticorrosion agent
3.2.2.3 Waxes and polishes
3.2.2.4 Optical brighteners
3.2.2.5 Catalysts
3.2.2.6 Pharmaceuticals
3.2.2.7 Bactericides, fungicides and herbicides
3.2.2.8 Food additive applications
3.2.2.9 Cosmetics
4. ENVIRONMENTAL TRANSPORT, DISTRIBUTION AND TRANSFORMATION
4.1. Transport and distribution between media
4.1.1. Volatilization
4.2. Transformation
4.2.1. Biodegradation
4.2.1.1 Batch biodegradation tests
4.2.1.2 Biodegradation in laboratory-scale
wastewater treatment plants
4.2.2. Abiotic degradation
4.2.2.1 Hydrolytic degradation
4.2.2.2 Photochemical degradation
4.2.2.3 Degradation by physico-chemical
processes
4.2.3. Bioaccumulation
4.3. Interaction with other physical, chemical or biological
factors
4.4. Ultimate fate following use
4.4.1. Fate of morpholine in various products
4.4.2. Waste disposal
5. ENVIRONMENTAL LEVELS AND HUMAN EXPOSURE
5.1. Environmental levels
5.1.1. Ambient air
5.1.2. Water
5.1.2.1 River water
5.1.2.2 Wastewater
5.1.3. Sediment
5.1.4. Soil
5.1.5. Terrestrial and aquatic organisms
5.2. General population exposure
5.2.1. Indoor air
5.2.2. Drinking-water and food
5.2.3. Tobacco
5.2.4. Cosmetics and toiletry articles
5.2.5. Rubber articles
5.3. Occupational exposure during manufacture, formulation or
use
5.3.1. Exposure to morpholine
5.3.2. Exposure to N-nitrosomorpholine
6. KINETICS AND METABOLISM IN LABORATORY ANIMALS AND HUMANS
6.1. Absorption
6.2. Distribution
6.3. Metabolic transformation
6.4. Elimination and excretion
6.4.1. Expired air
6.4.2. Urine
6.4.3. Faeces
6.5. Retention and turnover
7. EFFECTS ON LABORATORY MAMMALS AND IN VITRO TEST SYSTEMS
7.1. Single exposure
7.1.1. Oral
7.1.2. Inhalation
7.1.3. Dermal
7.1.4. Intraperitoneal
7.2. Short-term exposure
7.2.1. Oral
7.2.2. Inhalation
7.2.3. Dermal
7.3. Long-term exposure
7.3.1. Oral
7.3.2. Inhalation
7.3.3. Dermal
7.4. Skin and eye irritation; sensitization
7.4.1. Eye irritation
7.4.2. Skin irritation
7.4.3. Sensitization
7.5. Reproductive toxicity, embryotoxicity and teratogenicity
7.6. Mutagenicity and related end-points
7.6.1. Mutagenicity of morpholine
7.6.1.1 Bacteria
7.6.1.2 Yeast
7.6.1.3 Mammalian cells in vitro
7.6.1.4 In vivo studies in mammals
7.6.2. Mutagenicity of morpholine in the presence of
nitrite and nitrate
7.6.3. Mutagenicity of N-Nitrosomorpholine
7.7. Carcinogenicity
7.7.1. Morpholine
7.7.1.1 Oral studies
7.7.1.2 Inhalation studies
7.7.2. Morpholine and nitrite
7.7.2.1 Oral studies
7.7.3. Carcinogenicity of N-nitrosomorpholine
7.8. Factors modifying toxicity; toxicity of metabolites
7.8.1. Factors modifying toxicity
7.8.2. Morpholine metabolites
7.9. Mechanisms of toxicity - mode of action
8. EFFECTS ON HUMANS
8.1. General population exposure
8.1.1. Controlled human studies
8.1.1.1 Organoleptic effects
8.1.2. Epidemiological studies
8.2. Occupational exposure
9. EFFECTS ON OTHER ORGANISMS IN THE LABORATORY AND FIELD
9.1. Laboratory experiments
9.1.1. Microorganisms
9.1.1.1 Microorganisms in water
9.1.1.2 Microorganisms in soil
9.1.1.3 Pathogenic microorganisms
9.1.2. Other aquatic organisms
9.1.2.1 Monocellular green algae
9.1.2.2 Invertebrates
9.1.2.3 Vertebrates
9.1.3. Terrestrial organisms
9.1.3.1 Plants
9.1.3.2 Animals
9.2. Field observations
10. PREVIOUS EVALUATIONS BY INTERNATIONAL BODIES
REFERENCES
RESUME ET EVALUATION, CONCLUSIONS ET RECOMMANDATIONS
RESUMEN Y EVALUACION, CONCLUSIONES Y RECOMENDACIONES
NOTE TO READERS OF THE CRITERIA MONOGRAPHS
Every effort has been made to present information in the criteria
monographs as accurately as possible without unduly delaying their
publication. In the interest of all users of the Environmental Health
Criteria monographs, readers are requested to communicate any errors
that may have occurred to the Director of the International Programme
on Chemical Safety, World Health Organization, Geneva, Switzerland, in
order that they may be included in corrigenda.
* * *
A detailed data profile and a legal file can be obtained from the
International Register of Potentially Toxic Chemicals, Case postale
356, 1219 Châtelaine, Geneva, Switzerland (Telephone No. 9799111).
* * *
This publication was made possible by grant number 5 U01
ES02617-15 from the National Institute of Environmental Health
Sciences, National Institutes of Health, USA, and by financial support
from the European Commission.
Environmental Health Criteria
PREAMBLE
Objectives
In 1973 the WHO Environmental Health Criteria Programme was
initiated with the following objectives:
(i) to assess information on the relationship between exposure to
environmental pollutants and human health, and to provide
guidelines for setting exposure limits;
(ii) to identify new or potential pollutants;
(iii) to identify gaps in knowledge concerning the health effects of
pollutants;
(iv) to promote the harmonization of toxicological and
epidemiological methods in order to have internationally
comparable results.
The first Environmental Health Criteria (EHC) monograph, on
mercury, was published in 1976 and since that time an ever-increasing
number of assessments of chemicals and of physical effects have been
produced. In addition, many EHC monographs have been devoted to
evaluating toxicological methodology, e.g., for genetic, neurotoxic,
teratogenic and nephrotoxic effects. Other publications have been
concerned with epidemiological guidelines, evaluation of short-term
tests for carcinogens, biomarkers, effects on the elderly and so
forth.
Since its inauguration the EHC Programme has widened its scope,
and the importance of environmental effects, in addition to health
effects, has been increasingly emphasized in the total evaluation of
chemicals.
The original impetus for the Programme came from World Health
Assembly resolutions and the recommendations of the 1972 UN Conference
on the Human Environment. Subsequently the work became an integral
part of the International Programme on Chemical Safety (IPCS), a
cooperative programme of UNEP, ILO and WHO. In this manner, with the
strong support of the new 14 partners, the importance of occupational
health and environmental effects was fully recognized. The EHC
monographs have become widely established, used and recognized
throughout the world.
The recommendations of the 1992 UN Conference on Environment and
Development and the subsequent establishment of the Intergovernmental
Forum on Chemical Safety with the priorities for action in the six
programme areas of Chapter 19, Agenda 21, all lend further weight to
the need for EHC assessments of the risks of chemicals.
Scope
The criteria monographs are intended to provide critical reviews
on the effect on human health and the environment of chemicals and of
combinations of chemicals and physical and biological agents. As
such, they include and review studies that are of direct relevance for
the evaluation. However, they do not describe every study carried
out. Worldwide data are used and are quoted from original studies,
not from abstracts or reviews. Both published and unpublished reports
are considered and it is incumbent on the authors to assess all the
articles cited in the references. Preference is always given to
published data. Unpublished data are only used when relevant
published data are absent or when they are pivotal to the risk
assessment. A detailed policy statement is available that describes
the procedures used for unpublished proprietary data so that this
information can be used in the evaluation without compromising its
confidential nature (WHO (1990) Revised Guidelines for the Preparation
of Environmental Health Criteria Monographs. PCS/90.69, Geneva, World
Health Organization).
In the evaluation of human health risks, sound human data,
whenever available, are preferred to animal data. Animal and
in vitro studies provide support and are used mainly to supply
evidence missing from human studies. It is mandatory that research on
human subjects is conducted in full accord with ethical principles,
including the provisions of the Helsinki Declaration.
The EHC monographs are intended to assist national and
international authorities in making risk assessments and subsequent
risk management decisions. They represent a thorough evaluation of
risks and are not, in any sense, recommendations for regulation or
standard setting. These latter are the exclusive purview of national
and regional governments.
Content
The layout of EHC monographs for chemicals is outlined below.
* Summary - a review of the salient facts and the risk evaluation
of the chemical
* Identity - physical and chemical properties, analytical methods
* Sources of exposure
* Environmental transport, distribution and transformation
* Environmental levels and human exposure
* Kinetics and metabolism in laboratory animals and humans
* Effects on laboratory mammals and in vitro test systems
* Effects on humans
* Effects on other organisms in the laboratory and field
* Evaluation of human health risks and effects on the
environment
* Conclusions and recommendations for protection of human health
and the environment
* Further research
* Previous evaluations by international bodies, e.g., IARC, JECFA,
JMPR
Selection of chemicals
Since the inception of the EHC Programme, the IPCS has organized
meetings of scientists to establish lists of priority chemicals for
subsequent evaluation. Such meetings have been held in: Ispra, Italy,
1980; Oxford, United Kingdom, 1984; Berlin, Germany, 1987; and North
Carolina, USA, 1995. The selection of chemicals has been based on the
following criteria: the existence of scientific evidence that the
substance presents a hazard to human health and/or the environment;
the possible use, persistence, accumulation or degradation of the
substance shows that there may be significant human or environmental
exposure; the size and nature of populations at risk (both human and
other species) and risks for environment; international concern, i.e.
the substance is of major interest to several countries; adequate data
on the hazards are available.
If an EHC monograph is proposed for a chemical not on the
priority list, the IPCS Secretariat consults with the Cooperating
Organizations and all the Participating Institutions before embarking
on the preparation of the monograph.
Procedures
The order of procedures that result in the publication of an EHC
monograph is shown in the flow chart. A designated staff member of
IPCS, responsible for the scientific quality of the document, serves
as Responsible Officer (RO). The IPCS Editor is responsible for
layout and language. The first draft, prepared by consultants or,
more usually, staff from an IPCS Participating Institution, is based
initially on data provided from the International Register of
Potentially Toxic Chemicals, and reference data bases such as Medline
and Toxline.
The draft document, when received by the RO, may require an
initial review by a small panel of experts to determine its scientific
quality and objectivity. Once the RO finds the document acceptable as
a first draft, it is distributed, in its unedited form, to well over
150 EHC contact points throughout the world who are asked to comment
on its completeness and accuracy and, where necessary, provide
additional material. The contact points, usually designated by
governments, may be Participating Institutions, IPCS Focal Points, or
individual scientists known for their particular expertise. Generally
some four months are allowed before the comments are considered by the
RO and author(s). A second draft incorporating comments received and
approved by the Director, IPCS, is then distributed to Task Group
members, who carry out the peer review, at least six weeks before
their meeting.
The Task Group members serve as individual scientists, not as
representatives of any organization, government or industry. Their
function is to evaluate the accuracy, significance and relevance of
the information in the document and to assess the health and
environmental risks from exposure to the chemical. A summary and
recommendations for further research and improved safety aspects are
also required. The composition of the Task Group is dictated by the
range of expertise required for the subject of the meeting and by the
need for a balanced geographical distribution.
The three cooperating organizations of the IPCS recognize the
important role played by nongovernmental organizations.
Representatives from relevant national and international associations
may be invited to join the Task Group as observers. While observers
may provide a valuable contribution to the process, they can only
speak at the invitation of the Chairperson. Observers do not
participate in the final evaluation of the chemical; this is the sole
responsibility of the Task Group members. When the Task Group
considers it to be appropriate, it may meet in camera.
All individuals who as authors, consultants or advisers
participate in the preparation of the EHC monograph must, in addition
to serving in their personal capacity as scientists, inform the RO if
at any time a conflict of interest, whether actual or potential, could
be perceived in their work. They are required to sign a conflict of
interest statement. Such a procedure ensures the transparency and
probity of the process.
When the Task Group has completed its review and the RO is
satisfied as to the scientific correctness and completeness of the
document, it then goes for language editing, reference checking, and
preparation of camera-ready copy. After approval by the Director,
IPCS, the monograph is submitted to the WHO Office of Publications for
printing. At this time a copy of the final draft is sent to the
Chairperson and Rapporteur of the Task Group to check for any errors.
It is accepted that the following criteria should initiate the
updating of an EHC monograph: new data are available that would
substantially change the evaluation; there is public concern for
health or environmental effects of the agent because of greater
exposure; an appreciable time period has elapsed since the last
evaluation.
All Participating Institutions are informed, through the EHC
progress report, of the authors and institutions proposed for the
drafting of the documents. A comprehensive file of all comments
received on drafts of each EHC monograph is maintained and is
available on request. The Chairpersons of Task Groups are briefed
before each meeting on their role and responsibility in ensuring that
these rules are followed.
WHO TASK GROUP ON ENVIRONMENTAL HEALTH CRITERIA FOR MORPHOLINE
Members
Dr J. Kielhorn, Fraunhofer Institute of Toxicology and Aerosol
Research, Hanover, Germany (Joint Rapporteur)
Dr J.S. Knapp, Department of Microbiology, University of Leeds, Leeds,
United Kingdom (Joint Rapporteur)
Dr I. Linhart, Centre of Industrial Hygiene and Occupational Diseases,
National Institute of Public Health, Prague, Czech Republic
Dr U. Schiecke, Federal Environmental Agency, Berlin, Germany
Dr J.A. Sokal, Institute of Occupational Medicine and Environmental
Health, Sosnowiec, Poland (Chairman)
Representatives of other organizations
Dr P. Montuschi, Department of Pharmacology, Catholic University of
the Sacred Heart, Rome, Italy (representing the International
Union of Toxicology (Vice-Chairman)
Secretariat
Mrs C. Partensky, International Agency for Research on Cancer, Lyon,
France
Dr E. Smith, International Programme on Chemical Safety, World Health
Organization, Geneva, Switzerland (Secretary)
ENVIRONMENTAL HEALTH CRITERIA FOR MORPHOLINE
A WHO Task Group on Environmental Health Criteria for Morpholine
met at the World Health Organization, Geneva, from 8 to 11 November
1994. Dr E.M. Smith, IPCS, welcomed the participants on behalf of Dr
M. Mercier, Director of the IPCS, and on behalf of the heads of the
three IPCS cooperating organizations (UNEP/ILO/WHO). The Task Group
reviewed and revised the draft monograph and made an evaluation of the
risks for human health and the environment from exposure to
morpholine.
The first draft of this monograph was prepared by Dr J. Kielhorn
and Dr G. Rosner, Fraunhofer Institute of Toxicology and Aerosol
Research, Hanover, Germany. The second revised draft was prepared by
Dr J. Kielhorn. Dr E.M. Smith and Dr P.G. Jenkins, both members of
the IPCS Central Unit, were responsible for the scientific content and
technical editing, respectively.
The efforts of all who helped in the preparation and finalization
of the monograph are gratefully acknowledged.
ABBREVIATIONS
CHO Chinese hamster ovary
DOC dissolved organic carbon
FID flame ionization detector
FPD flame photometric detector
GC gas chromatography
HPLC high-performance liquid chromatography
IC ion chromatography
MLSS mixed liquor suspended solids
MS mass spectrometry
NMOR N-nitrosomorpholine
NO nitrogen oxide
NOAEL no-observed-adverse-effect level
NSD nitrogen selective detector
OECD Organisation for Economic Co-operation and Development
TEA thermal energy analyser
1. SUMMARY AND EVALUATION, CONCLUSIONS AND RECOMMENDATIONS
1.1 Physical and chemical properties
Morpholine (1-oxa-4-azacyclohexane) is a colourless, oily,
hygroscopic, volatile liquid with a characteristic amine ("fishy")
odour. It is completely miscible with water, as well as with many
organic solvents, but has limited solubility in alkaline aqueous
solutions. It is a base, the pKa of the conjugated acid being 8.33.
Correspondingly, the octanol-water partition coefficient is pH-
dependent (log Pow -2.55 at pH 7 and -0.84 at pH 10; 35°C). The
vapour pressure of aqueous solutions of morpholine is very close to
that of water.
Morpholine can undergo a variety of reactions. It behaves
chemically as a secondary amine. Under environmental and
physiological conditions, the proven animal carcinogen
N-nitrosomorpholine (NMOR) is formed by reaction of solutions of
nitrite or gaseous nitrogen oxides with dilute solutions of
morpholine. Nitrogen oxide (NO) levels may be of importance in
nitrosation. The conditions of nitrosation, in particular pH, play a
significant role.
1.2 Analytical methods
Morpholine can be determined by gas chromatography (GC) with
packed as well as capillary columns, high-performance liquid
chromatography (HPLC) and ion chromatography (IC). Detectors used
include flame ionization detector (FID), flame photometric detector
(FPD), nitrogen selective detector (NSD), and mass spectrometry (MS)
and thermal energy analyser (TEA) for GC, and UV-detector and TEA for
HPLC. For the determination of trace amounts, derivatization is
required. The method of choice for sensitivity seems to be GC with
TEA following the derivatization to NMOR (the detection limit is
2-3 µg/kg in various matrices). Low concentrations of morpholine in
air can be determined by GC with NSD.
1.3 Sources of human and environmental exposure
It is estimated that around 25 000 tonnes of morpholine per year
are produced industrially world-wide, but details of production from
some countries are lacking.
The main production process used appears to be the reaction of
diethylene glycol with ammonia in the presence of hydrogen and
catalysts.
Morpholine is an extremely versatile chemical but knowledge of
its uses is incomplete. It is important as a chemical intermediate in
the rubber industry, as a corrosion inhibitor, and in the synthesis of
optical brighteners, crop protection agents, dyes and drugs.
Morpholine is used as a solvent for a large variety of organic
materials, including resins, dyes and waxes. It can be used as a
catalyst. Morpholine is still used in some countries in toiletry and
cosmetic products. It is used in some countries in several direct and
indirect food additive applications.
Human and environmental exposure arises from both gaseous and
aqueous emissions and directly from some of its uses, including, for
example, its use in cosmetic formulations and waxes. The main
emissions probably result from its manufacture and its use in the
chemical industry (notably in production and use of rubber chemicals)
and as an anti-corrosion agent. Morpholine has been detected in a
wide variety of foods and tobacco. It could be that this morpholine
arises from the wax coatings on fruit or on packaging, but in some
cases its origin is unknown.
1.4 Environmental transport, distribution and transformation
Morpholine is chemically stable in the biosphere although it is
subject to chemical and biological nitrosation to NMOR.
Morpholine is inherently biodegradable. Under the conditions of
model activated sludge plants, morpholine is biodegradable. However,
under non-adapted conditions there is probably no significant
degradation of morpholine. The mean solid retention time in activated
sludge plants is of crucial importance and must be over 8 days if
reliable morpholine degradation is to be achieved.
There are inadequate data on the bioaccumulation of morpholine in
aquatic and terrestrial organisms. From the n-octanol/water
partition coefficient for morpholine (log Pow = -2.55 at pH7), no
bioaccumulation would be expected.
As morpholine is an important industrial chemical with a wide
range of applications, the presence of the compound or its derivatives
is to be expected in many industrial effluents. Its use as a
corrosion inhibitor in boiler water means that it will be found in
boiler wastewater, including that from power plants using morpholine.
Its use in the manufacture of rubber additives results in an
undefinable amount of morpholine being released into the hydrosphere
or geosphere through tyre abrasion and disposal of used tyres.
As a result of its use in waxes and polishes, morpholine is
released into the environment through volatilization. It is quickly
adsorbed by moisture. The main compartment for accumulation of
morpholine is therefore the hydrosphere. The limited data suggest that
morpholine does not accumulate in the hydrosphere.
Incineration is the preferred method of disposal for undiluted
morpholine, but nitrogen oxide emission controls may be required to
meet environmental regulations. For aqueous effluents, activated
sludge treatment is adequate, but only if the plant is carefully
controlled (see above).
1.5 Environmental levels and human exposure
There are no data available on levels of morpholine in ambient
and residential indoor air and in drinking-water. There are limited
data on its occurrence in natural waters and no information on its
occurrence in soil.
Based on the available data, the main source of general
population exposure to morpholine is food, which can be contaminated
with morpholine through direct treatment of fruit with waxes
containing morpholine for conservation purposes, through steam
treatment during food processing, and by the use of packaging material
containing morpholine. However, quantitative data on food
contamination by morpholine and NMOR are limited. For example, in
prepacked milk products, values ranged from 5 to 77 µg/kg morpholine
and up to 3.3 µg/kg NMOR. Morpholine content in various food samples
(fish, meat, plant products, beverages) usually did not exceed
1 mg/kg. Higher levels (up to 71.1 mg/kg) were detected in citrus
fruits in Japan. A survey in Italy did not identify NMOR in a variety
of foods at a detection limit of 0.3 µg/kg. Existing data do not
permit an estimation of the intake of morpholine and NMOR from food.
Morpholine has been found in cigarette tobacco at a concentration
of 0.3 mg/kg, and in snuff and chewing tobacco at concentrations up to
4.0 mg/kg. Levels of NMOR up to 0.7 mg/kg have been reported in the
past in snuff. These were probably associated with the use of
morpholine-containing waxes in packaging.
NMOR has been detected in some toiletry and cosmetic products,
e.g., shampoos and eye make-up, and in rubber articles, e.g. baby
pacifiers and feeding bottle teats, at levels up to 3.5 mg/kg.
Occupational exposure to morpholine may occur in several
industries. There are few data on exposure of workers to morpholine.
All reported values are below 3 mg/m3. Occupational exposure to
NMOR has been found in the rubber industry, where concentrations up to
250 µg/m3 have been measured.
The data currently available provide an indication of the
potential for human exposure but do not allow a precise estimation of
the levels of exposure of the general and occupational populations to
morpholine and NMOR.
1.6 Kinetics and metabolism in laboratory animals and humans
Morpholine is absorbed after oral, dermal and inhalation
exposure. In the rat following oral and intravenous administration,
morpholine is rapidly distributed, the highest concentrations being
found in the intestine and muscle.
In the rabbit, following intravenous and inhalation exposure,
morpholine is preferentially distributed to the kidneys, lower
concentrations reaching the lung, liver and blood.
Morpholine does not bind significantly to plasma proteins.
Plasma half-lives have been reported to be 115 (rat), 120 (hamster),
and 300 min (guinea-pig).
Morpholine is excreted mainly via the renal route, as the
unchanged compound, in a variety of species. One day after
administration, 70-90% of morpholine was found in urine.
Neutralization of morpholine enhances the rate of excretion of the
compound. A small percentage of morpholine is excreted in expired air
and faeces.
Studies in rats, mice, hamster and rabbit indicate that
morpholine is eliminated almost completely as the unmetabolized
compound. In the guinea-pig, N-methylation followed by Noxidation
can occur, with up to 20% of the administered dose being metabolized.
In the presence of nitrite, morpholine can be converted to NMOR both
in vitro and in vivo. Depending on the dose, 0-12% of morpholine
administered to rats with nitrites may be nitrosated.
Immunostimulation, involving macrophage activation, may increase
the extent of nitrosation.
1.7 Effects on laboratory mammals and in vitro test systems
The acute toxicity of morpholine after oral administration shows
LD50 values of 1-1.9 g/kg body weight and 0.9 g/kg body weight in
the rat and guinea-pig, respectively. Rats receiving neutralized
morpholine (1 g/kg body weight) survived. After intraperitoneal
administration, the LD50 was 0.4 g/kg body weight in the mouse and
between 0.1 and 0.4 g/kg body weight in the rat. After inhalation
exposure, the LD50 was about 8 g/m3 in the rat and between 5 and
7 g/m3 in the mouse. The dermal LD50 was 0.5 ml/kg of undiluted
morpholine in the rabbit. The acute toxicity of morpholine is
characterized by gastrointestinal haemorrhage and diarrhoea after oral
exposure, and irritation and haemorrhage of the nose, mouth, eyes and
lung after inhalation. In a 30-day gavage study on rats at doses of
0.16 - 0.8 g/kg body weight, there were severe toxic effects and
mortality at all dose levels. In the guinea-pig at doses of
0.09 - 0.45 g/kg body weight there was also severe toxicity and
mortality at all dose levels.
After short-term inhalation exposure to morpholine (7.2 g/m3,
4 h/day, 4 days and 1.63 g/m3, 4 h/day, 5 days/week, 30 days),
alterations in lung function have been reported in rats. Mortality
rate in the rat ranged from 0 to 100% depending on exposure level
(0.36-18.1 g/m3, 6 h/day, 9 days). Inhalation toxicity was dose-
related with various degrees of local irritation (eyes, mouth, nose,
lung) and haemorrhage at the higher exposure levels. One study
reported increased function of thyroid gland and another necrosis of
liver and renal tubules after inhalation exposure.
A 90-day study showed that morpholine administered orally
(0.2-0.7 g/kg body weight per day) for 90 days may reduce body weight
gain and renal function in the mouse. After 672 days of oral exposure
to morpholine (0.28-0.5 g/kg body weight per day), forestomach
epithelium hyperplasia was reported (mouse).
In a 13-week inhalation study, morpholine (0.09-0.9 g/m3,
6 h/day, 5 days/week) has been reported to cause dose-related lesions
of nasal mucosa and pneumonia at the higher exposure levels (0.36 and
0.9 mg/m3). No treatment-related changes to a number of parameters
were observed at 0.09 g/m3; this concentration may be considered a
no-observed-adverse-effect level (NOAEL) under the conditions of
sub-chronic inhalation exposure.
Morpholine in the undiluted and unneutralized form is highly
irritant for the eye and skin, probably due to its alkaline
properties. Dilution and neutralization of its pH may significantly
reduce its topical toxicity. Morpholine (2%) did not induce
sensitivity in the guinea-pig using the modified Buehler method.
Morpholine did not induce mutations in bacteria or yeasts with
and without metabolic activation (with one exception at a very high
concentration). It was negative in the host-mediated assay.
Morpholine did not induce DNA-repair in primary rat hepatocytes
and did not induce a significant increase in sister chromatid exchange
in Chinese hamster ovary cells. Morpholine was considered to be weakly
mutagenic in the L5178Y mouse lymphoma assay. It increased type III
foci in the BALB/3T3 malignant cell transformation assay, although
neutralized morpholine did not.
Morpholine caused neither point mutation nor chromosomal
aberration in hamster embryos exposed in utero.
No increase in the incidence of tumours was seen in rats given up
to 0.5 g/m3 morpholine by inhalation for 104 weeks nor in mice given
1% morpholine oleate in their drinking-water for 96 weeks. In a long-
term study on a group of 104 rats given 1000 mg morpholine/kg diet,
there were three liver cell carcinoma, two lung and another
angiosarcoma (unspecified) and two malignant glioma, whereas in a
control group of 156 rats there were no tumours. With hamsters under
the same conditions, no tumours were found.
Morpholine given simultaneously with nitrite yields positive
results in the host-mediated assay, probably due to the formation of
NMOR. Morpholine fed simultaneously with nitrite induced liver and
lung tumours in rats and liver tumours in hamsters probably due to the
endogenous formation of NMOR. NMOR is mutagenic in bacteria and
yeasts; weakly positive results were reported for sister chromatid
exchange in CHO cells and for mutations in mouse lymphoma L5178Y
cells. NMOR is carcinogenic in mice, rats, hamsters and various
fishes, producing liver and lung tumours in mice, liver, kidney and
blood vessel tumours in rats, liver, upper digestive and respiratory
tract tumours in hamsters, and liver tumours in fish.
1.8 Effects on humans
There have been no reports on incidents of acute poisoning or on
the effects of short- or long-term exposure to morpholine by the
general population.
The phenomenon known as blue vision or glaucopsia, as well as
some instances of skin and respiratory tract irritation, have been
described in reports of occupational exposure to morpholine; however,
no atmospheric concentrations of morpholine were given. It was
reported that the number of chromosomal aberrations in the lymphocytes
of peripheral blood of workers exposed for 3-10 years to morpholine at
concentrations of 0.54-0.93 mg/m3 did not differ significantly from
controls.
Undiluted morpholine is strongly irritant to skin; a dilute
solution (1 to 40) was mildly irritant.
The potential carcinogenicity of morpholine in exposed human
populations has not been investigated.
1.9 Effects on other organisms in the laboratory and field
Among the aquatic organisms tested, certain cyanobacteria
(Microcystis) and unicellular green algae (Scenedesmus) appear to
be the most sensitive taxa as toxicity threshold values (criterion:
inhibition of population growth) of 1.7 mg/litre for Microcystis and
4.1 mg/litre for Scenedesmus have been reported (duration of
exposure: 8 days).
Aerobic bacteria like Pseudomonas proved to be much more
resistant: the 16-h toxicity threshold and the NOEC for population
growth have been cited as 310 and 8700 mg/litre, respectively.
However, 1000 mg/litre inhibited respiration and dehydrogenase
activity (up to 20%) in activated sludge from industrial treatment
plants.
Among aquatic protozoans tested so far, representatives of the
genera Entosiphon and Chilomonas (with threshold values of 12 and
18 mg/litre, respectively, for the inhibition of population growth)
turned out to be the most sensitive. The 24-h EC values
(E=immobilisation) for Daphnia were in the range of
100-120 mg/litre. The 48- to 96-h LC50 values reported for fish
tested in fresh, brackish or seawater were > 180 mg/litre, rainbow
trout being the most sensitive species.
No data on long-term effects in aquatic invertebrates and
vertebrates are available. Information about the toxicity of
morpholine in free-living soil organisms is almost entirely lacking,
being restricted to a 3-day EC value of about 400 mg/litre given for
germination inhibition in lettuce.
1.10 Evaluation of human health risks and effects on the environment
1.10.1 Evaluation of effects on human health
The general population is primarily exposed to morpholine by
consumption of contaminated food. Contamination of tobacco and
tobacco products, and cosmetic and toiletry articles and rubber
products may also contribute to overall exposure. Occupational
exposure to morpholine occurs in many industries; the compound is
absorbed by inhalation and skin absorption. Data are inadequate to
determine the degree of exposure of the general population. Data on
occupational exposure to morpholine are also limited.
Morpholine is not highly toxic under conditions of acute
exposure. The LD50 after oral administration is 1-1.9 g/kg body
weight in rats and 0.9 g/kg body weight in guinea-pigs. LC50 values
of 7.8 mg/m3 (rats) and 4.9-6.9 g/m3 (mice) have been reported.
In the conditions of short-term and long-term inhalation
exposure, the critical effects appear to be irritation of the eyes and
respiratory tract. A concentration of 90 mg/m3 may be considered the
NOAEL in the conditions of the 13-week experiment in rats (6 h/day,
5 days/week). In a long-term inhalation study (104 weeks), increased
incidences of inflammation of the cornea, and inflammation and
necrosis of the nasal cavity were observed in rats at 540 mg/m3.
Increased incidence of irritation of eyes and nose was also observed
at 36 and 180 mg/m3.
High exposures to morpholine causes severe damage to the liver
and kidneys of rats and guinea-pigs. Fatty degeneration of the liver
was reported in rats after feeding morpholine (0.5 g/kg body weight)
daily for 56 days. When administered morpholine oleic acid salt in
the drinking-water at a dose of about 0.7 g/kg body weight per day for
13 weeks, mice showed cloudy swelling of the kidney proximal tubules.
Decreased body weight gain was observed in female mice in the long-
term (672 days) feeding experiment at dose levels between 0.05 and
0.4 g morpholine (as oleic acid salt).
At the reported levels of the present occupational and
environmental exposures, morpholine does not seem to create any
significant risk of systemic toxic effects. Local effects (irritation)
of the eyes and respiratory tract may occur in non-controlled
occupational and incidental exposures to high concentrations of
airborne morpholine, and skin irritation may result from contact with
liquid (even diluted) morpholine.
Morpholine does not appear to be mutagenic or carcinogenic in
animals. However, it can be easily nitrosated to form NMOR, which is
mutagenic and carcinogenic in several species of experimental animals.
Morpholine fed to rats sequentially with nitrite caused an increase in
tumours, mostly hepatocellular carcinoma and sarcomas of the liver and
lungs. It is therefore prudent to consider exposure to morpholine as
increasing the carcinogenic risk in exposed populations.
1.10.2 Evaluation of effects on the environment
In view of the very restricted knowledge regarding environmental
exposure, the lack of effect data relating to long-term exposure in
water and to short- and long-term exposure in the terrestrial
environment, a sound risk assessment cannot be carried out at present.
On the basis of the reported properties of morpholine, the available
ecotoxicological information and the few data on environmental
concentrations, certain conclusions can be drawn.
The high water solubility of morpholine and its low volatility
(under environmental conditions) make the hydrosphere the pre-dominant
environmental sink.
Morpholine is inherently biodegradable and, although degradation
is slow, there are no data to suggest accumulation in the hydrosphere.
Bioaccumulation is unlikely.
There are relatively few data on toxicity of morpholine to free-
living organisms. However, it seems unlikely that current levels of
morpholine emission cause any significant damage to the wider
environment. Local effects, due for example to factory emissions or
to morpholine release due to wear of tyres, remain to be evaluated.
Contamination of some foods, e.g., fish, with morpholine may be
due to environmental contamination, but this is uncertain.
Conversion of morpholine to NMOR is the main cause of concern,
especially with respect to vertebrate populations. NMOR has been
reported in industrial wastewater and in soil near a factory. The
presence of morpholine in water destined for processing to drinking-
water is a cause for concern.
1.11 Conclusions and recommendations
Morpholine does not present a toxic risk to humans at the usual
levels of exposure, but its conversion to the carcinogenic NMOR should
be noted.
There is no evidence at present levels of exposure that
morpholine poses a substantial risk to biota in the environment.
1.11.1 Recommendations for protection of human health
a) Human exposure to morpholine should be avoided as far as
possible.
b) Contamination of food through food packaging and food processing
should be avoided.
c) Morpholine should not be used in rubber products intended for
direct contact with humans.
d) Morpholine should not be used in toiletry or cosmetic
preparations.
e) Industrial effluents should be rigorously treated to avoid entry
of morpholine into drinking-water.
f) In the light of the formation of carcinogenic NMOR the present
occupational exposure limits should be reconsidered.
1.11.2 Recommendations for protection of the environment
Spills and shock loads to effluent treatment plants should be
avoided.
1.11.3 Recommendations for further research
Studies should be undertaken on the following topics:
a) reproductive toxicity in mammals;
b) long-term toxicity in mammals;
c) effect of exposure of mammals to low levels of morpholine with
and without nitrite and nitrate;
d) transnitrosation by NMOR under in vivo and in vitro
conditions;
e) biodegradation under anaerobic conditions, especially under
nitrate-reducing conditions;
f) microbial catalysis of N-nitrosation under realistic
conditions;
g) environmental levels of morpholine in groundwater, soil and
rivers used for drinking-water;
h) environmental levels of morpholine around morpholine-producing
and -processing factories;
i) metabolism and toxicokinetics in humans as a part of the
development of methods for biological monitoring of morpholine;
j) monitoring of morpholine and NMOR levels in food, drinking-water
and indoor air;
k) data on occupational exposure should be collected and made
available.
2. IDENTITY, PHYSICAL AND CHEMICAL PROPERTIES, AND ANALYTICAL METHODS
2.1 Identity
CAS/IUPAC name: Morpholine
Chemical formula: C4H9NO
Chemical structure: 
CAS registry number: 110-91-8
EEC number: 613-028-00-9
EINECS number: 2038151
UN number: 2054
Synonyms: 1-oxa-4-azacyclohexane
tetrahydro-2H-1,4-oxazine
tetrahydro-1,4-oxazine
tetrahydro-1,4-isoxazine
diethylene oximide
diethyleneimide oxide
diethylene imidoxide
Relative molecular mass: 87.12
2.1.1 Technical product
The compound is marketed under the name of "Morpholine". It is
distributed as an anhydrous liquid and as 40% and 88% solutions with
water (Air Products and Chemicals, 1989).
2.1.2 Impurities
Morpholine is marketed as a product with approximately 99% purity
(Cosmetic Ingredient Review, 1989; BUA, 1991). The exact chemical
nature of the impurities depends on the production process (see
section 3.2.1.3). When produced from diethylene glycol,
2-(2-aminoethoxy)ethanol is a by-product, which can be isolated and
recycled (Heilen et al., 1989). Reported impurities are
N-ethylmorpholine and ethylenediamine (Heilen et al., 1989) and
2-methoxy ethanol (BUA, 1991).
During the production of morpholine from diethanolamine, it is
possible that N-hydroxyethylmorpholine may be formed (Cosmetic
Ingredient Review, 1989).
Impurities in cosmetic grade morpholine have been reported to
include arsenic (up to 3 mg/kg) and lead (up to 20 mg/kg) (Estrin et
al., 1982). The Cosmetic Ingredient Review (1991a) lists morpholine
as having insufficient data on impurities.
Fajen et al. (1979) found 0.8 mg/kg N-nitrosomorpholine (NMOR)
in a morpholine charge used for the production of a vulcanization
accelerator in a chemical factory in Ohio. NMOR could not be detected
(detection limit: 50 µg/kg) in morpholine stored under nitrogen in
Germany (BUA, 1991).
2.2 Physical and chemical properties
2.2.1 Physical properties of morpholine
Morpholine is a colourless, oily, hygroscopic, volatile liquid
with a characteristic amine smell (Reinhardt & Brittelli, 1981).
Morpholine vapour is heavier than air and as a result, the vapour can
travel a significant distance to a source of ignition and "flash
back".
It is completely miscible with water, soluble in the usual
solvents and can itself be used as a solvent (Heilen et al., 1989).
It has a low solubility in alkaline aqueous solutions.
Morpholine is a strong base, the 0.01% (w/w) mixture having a
pH of 9.4, and the 10% (w/w) mixture having a pH of 11.2 (Texaco,
1986).
Some physical and chemical properties are presented in Table 1.
2.2.1.1 Storage of morpholine
Morpholine can be stored for an unlimited time in iron or steel
containers if protected from atmospheric moisture and carbon dioxide.
However, it is unstable in the presence of copper, zinc and their
alloys and these metals should not be used in storage containers for
morpholine (Heilen et al., 1989; Air Products and Chemicals, 1989).
2.2.2 Chemical properties of morpholine
Morpholine can undergo a diversity of reactions. It is an amino
ether; the ether function of the molecule is typically inert and most
of the reactions involve the secondary amine group.
Table 1. Some physical and chemical properties of morpholine
Melting point (°C) -3.1a; -4.9b,c; -5d
Boiling point (°C at 1013 hPa) 128.2a; 128.3c; 128.9b; 128-130d
Flash point (°C) - Open cup 38b;
- Closed cup 35c; 31d
Autoignition temperature (°C) 275a,d; 310c;
Explosion limits in air 1.4-13.1 vol% d; 1.8-11 vol% e;
1.8-15.2 vol% a
Decomposition temperature > 330°Cd; > 550°C
(in steam cycles)a
pKa (conjugated acid) 8.33 (25°C)f;
8.36c (temperature not given)
Vapour pressure (°C) 10 20 40 60 80 100 120
(kPa) 0.6 1.1 3.2 8.3 10.5 40.9 81.8
Density g/cm3 (20°C) 0.994b; 0.999c; 1.00d; 1.007a
log n-octanol/water partition -0.723 (free base; calculated)g
coefficient (log Pow) -1.08 (free base; calculated)h
-0.66 (free base; calculated)i
Solubility in water completely miscible with watera
Solubility in organic solvents completely miscible with, for
instance, methanol, ethanol, acetone,
diethylether, benzene, toluene,
xylolc,e
Refractive index 1.4537-1.4545 at 20°Ce
Human olfactory threshold 0.036 (mg/m3)j
a Heilen et al. (1989); b Brown (1966); c Texaco (1986);
d BASF (1987); e Cosmetic Ingredient Review (1989);
f Lide (1990); g UBA (1990); h Leo et al. (1971);
i Le Therizien et al. (1980); j Hellman & Small (1974)
It reacts with inorganic acids and acid gases such as CO2,
H2S, or HCN to form morpholine salts. This property is of use in
the addition of morpholine as an anticorrosive in boiler systems
(Brown, 1966). Morpholine can react with oxidizing agents, undergo
direct chlorination, and form complexes with metallic halides. It
reacts with carboxylic acids, anhydrides, chlorides and esters to form
morpholides (Brown, 1966). Alkyl morpholides are formed by reaction
of morpholine with alkyl halides, dialkyl sulfates or trialkyl
phosphates. The N-alkylmorpholides, particularly
N-methylmorpholides, and N-ethylmorpholides, are widely used as
catalysts in the preparation of polyurethanes (Brown, 1966).
Morpholine reacts with formaldehyde to form N-formyl-morpholine,
which is used industrially as a selective solvent for the extraction
of very pure aromatic compounds (Heilen et al., 1989).
Morpholine reacts with fatty acids to form soaps which are used
in household and automotive waxes and polishes. Their principal
advantage is that the morpholine evaporates at the same rate as water,
leaving a water-resistant wax base (Mjos, 1978; Texaco, 1986).
Vulcanizing agents for the rubber industry are formed by the reaction
of morpholine with sulfur and sulfur-containing compounds (Taylor &
Son, 1982).
Morpholine is flammable. Violent reaction and fire may result
when the product is mixed with oxidizing agents (Air Products and
Chemicals, 1989).
N-nitrosomorpholine (NMOR) can be formed by reaction of aqueous
solutions of nitrite with morpholine or by reaction of gaseous
nitrogen oxides in aqueous solutions of morpholine (see section 4.3).
2.3 Conversion factors for morpholine
1 mg/m3 = 0.276 ppm at 20°C and 1013 hPa
1 ppm = 3.62 mg/m3
2.4 Analytical methods
Methods suitable for measuring trace levels of morpholine include
ion chromatography (IC), gas chromatography (GC) with packed as well
as capillary columns, and high-performance liquid chromatography
(HPLC), usually using reverse phase (RP) columns.
The poor UV absorptivity of morpholine necessitates chemical
derivatization to detect trace amounts.
Detection methods include UV detectors (for HPLC) and flame
ionisation detectors (FID, following GC), as well as thermal energy
analysers (TEA). Photochemical methods are used but are not specific
for morpholine.
An overview of the analytical methods for determining morpholine
in various matrices is given in Table 2.
For the detection of trace amounts of NMOR, GC or HPLC together
with TEA has proved to be the method of choice. The use of internal
standards helps to distinguish NMOR in the sample from artifacts
caused by nitrosation or transnitrosation during the work-up procedure
(BUA,1991; ECETOC, 1991).
2.4.1 Determination of morpholine in air
Table 2 summarizes the available methods.
Air samples can be collected and concentrated by passing through
silica gel or an impinger containing dilute acid. A 20-litre sample
is recommended to reach concentrations between 7 and 210 mg/m3
(NIOSH, 1977). Bianchi & Muccioli (1978) collected air samples
without absorption on a solvent and rapidly performed the GC.
Sollenberg & Hansen (1987) described an isotachophoretic
determination of morpholine using 10 mM potassium cacodylate (pH 6.5)
as leading electrolyte, and 10 mM creatinine with 5 mM HCl as
terminating electrolyte. This method has been used primarily to
measure N-methylmorpholine in air samples from a polyurethane foam
factory (Hansen et al., 1986). Aarts et al. (1990) also used an
isotachophoretic method for determining morpholine in rubber samples
(see Table 2).
2.4.2 Determination of morpholine in water
The methods given in Table 2 (water) are suitable for the
determination of morpholine in steam condensates or non-aqueous
solvents.
2.4.3 Determination of morpholine in soil and sediments
A GC/MS method has been used to detect morpholine in sediment and
soil (Spies et al., 1987).
2.4.4 Determination in biological and other materials
Morpholine has been determined in biological tissues and fluids
using GC/FID (Tombropoulos, 1979). Morpholine and some of its
metabolites ( N-hydroxymorpholine, N-methylmorpholine and
N-methylmorpholine- N-oxide) could be separated using two
complementary HPLCs, one using reversed-phase and the other
ion-exchange chromatography (Sohn et al., 1982a).
Morpholine has been determined in a number of foods and beverages
as well as in tobacco, snuff and packaging material (see section
5.2.2). The methods used are summarized in Table 2. Generally,
morpholine is extracted from the samples using steam distillation
followed by purification and derivatization.
Table 2. Methods for the analysis of morpholinea
Matrix Sample preparation Methodb Detectorb Detection Recovery References
limit (%)
Air adsorption on silica gel, GC FID 7 mg/m3c 100 NIOSH (1977)
desorption with H2SO4,
neutralization with NaOH
Air collected directly GC FID 36 mg/m3 not given Bianchi &
Muccioli (1978)
Air absorption in 1 N KOH (impinger); GC TEA not given not given Fajen et al.
extraction with dichloromethane (1979)
Air adsorption on silica gel; HPLC UV not given 90-96 Simon & Lemacon
derivatization to m-toluamides (235-255 nm) (1987)
Air absorption on silica gel, GC NSD 0.03 mg/m3 93 ± 5% BIA (1989)
extraction with methanol
+ 2% KOH
Water derivatization to p-tosylamide, GC FID 70 ng/litre 45-67 Singer &
acidification with HCl (pH 1), Lijinsky (1976a)
extraction with diethylether
Water addition of Cu(II), CS2 in UV/VIS VIS 10 µg/litre 89 Karweik &
chloroform and NH3/NH4Cl-buffer (434 nm) Meyers (1979)
Water, with Ni(II); phosphate buffer HPLC UV not given 95-100 Moriyasu et al.
solutions (325 nm)d (1984)
Water Cu(II); remainder; titrated titration Cu-ion- lower 98 Hassan et al.
with EDTA selective mg range (1985)
electrode
Table 2 (cont'd)
Matrix Sample preparation Methodb Detectorb Detection Recovery References
limit (%)
Water derivatization with HPLC VIS < 10 µg/litrec 9-97 Koga &
1,2-naphthoquinone-4-sulfonate, (436 nm) Akiyama (1985)
extraction with dichloromethane
Water derivatization to benzene- GC FPD < 2 ng approx.100 Hamano et al.
sulfonamide; extraction with (1980)
n-hexane
Steam addition of KOH to pH > 10 GC FID 1 mg/litre > 90 Malaiyandi et
condensate al. (1979)
Steam none IC CD 100 µg/litre 91-97 Gilbert et al.
condensate (1984)
Steam acidification with HCl; derivatization HPLC VIS 30 µg/litre 96 Lamarre et al.
condensate to dabsyl amide, addition of NaHCO3 (456 nm) (1989)
Blood, extraction with methanol; purificaction GC FID < 4 mg/kgc 55-70 Tombropoulos
tissue, over picrate; neutralisation (tissue) (1979)
urine with CaCO3 < 21 mg/litrec
(blood/urine)
Urine, extraction with methanol homogenized HPLCe UV (196 nm) not given not given Sohn et al.
tissues in KCl, phosphate buffer, a) RP (1982a)
extraction with methane b) IC
Food, steam distillation; derivatization GC/GC-MS FID 200 µg/kg 45-67 Singer &
drinks to p-tosylamide (food) Lijinsky (1976a)
4 µg/litre
(drinks)
Table 2 (cont'd)
Matrix Sample preparation Methodb Detectorb Detection Recovery References
limit (%)
Food homogenization with HCl and GC FPD 10 µg/kg 89-100 Hamano et al.
methanol; derivatization to benzene (1981)
sulfonamide; extraction with n-hexane
Food, addition of alkali; injection GC TEA 87 µg/litre not given Rounbehler &
drinks of the liquid sample Fine (1982)
Citrus steam distillation GC/GC-MS FID 200 µg/kg 95; Ohnishi et al.
fruits 24-87f (1983)
Tobacco, steam distillation; derivatization GC/ FID < 0.3 mg/kgc 50 Singer &
smoke to p-tosylamide GC-MS Lijinsky (1976b)
condensate
Snuff, extraction with water; filtration; GC/ TEA 2 µg/kg 70-80 Brunnemann
tobacco, acidification; extraction with GC-MS et al. (1982)
packing diethylether; nitrosation;
material extraction with dichloromethane
Paper, extraction with HCl; nitrosation with GC TEA 3 µg/kg 90 Hotchkiss &
cardboard NaNO2; extraction with dichloromethane Vecchio (1983)
Rubber extraction/reextraction with GC PND 2 mg/kgc not given Lakritz &
articles dichloromethane/HCl HPLC Kimoto (1980)
Rubber air passed through powdered sample; isotachophoresis not given not given not given Aarts et al.
articles trapped in dil. HCl (1990)
a adapted from BUA (1991); b HPLC = high-performance liquid chromatography, UV = ultraviolet, GC = gas chromatography,
FID = flame ionisation detector, IC = ion chromatography, CD = conductivity detector, TEA = thermal energy analyser,
VIS = visible, FPD = flame photometric detection, PND = phosphorus nitrogen detector, NSD = nitrogen selective detector,
RP = reversed phase; c smallest measurable value (detection limit not given); d measured as diethyldithiocarbamate;
e method used primarily for the separation of morpholine metabolites; f removal efficiency of morpholine from peel
3. SOURCES OF HUMAN AND ENVIRONMENTAL EXPOSURE
3.1 Natural occurrence
Morpholine is not known to occur naturally.
3.2 Anthropogenic sources
3.2.1 Production levels and processes
3.2.1.1 World producers
a) Producers in USA (Chemical Marketing Reporter, 1989; 1990)
- Air Products and Chemicals
- BASF Co.
- Dow Chemical Co. (up to the end of 1990)
- Texaco Chemical Co.
b) Producers in western Europe (SRI, 1990)
- BASF AG, Ludwigshafen, Germany
- Chemische Werke Hüls AG, Marl, Germany (up to mid-1990)
- Texaco Ltd., Dyfed, Wales, United Kingdom
c) Producers in Japan (Japan Chemical Week, 1991)
- Koei Chemical
- Nippon Nyukazai
- Osaka Organic Chemical Ind.
d) Producers in other countries
Morpholine is manufactured in India and in the Common-wealth of
Independent States (CIS).
3.2.1.2 Production figures
Between 1974 and 1981, USA production was stable at about
11 000 tonnes/year (NRC, 1981). Two new plants were planned in the USA
in the 1980s, namely BASF (with an estimated capacity of
8200 tonnes/year) and Air Products and Chemicals (no capacity given).
BASF reported that in 1988 it manufactured morpholine at Geismar,
Louisiana, USA, as well as importing it from the parent plant in
Germany. The combined import/production volumes were about 30% of a
9000 tonnes/year market, i.e. 2700 tonnes per year (Dynamac
Corporation, 1988). In Germany, about 12 000 tonnes were produced
in 1988, around 75% being exported (BUA, 1991). Production figures
from other European countries are not available. In Japan,
1500-1600 tonnes/year is produced (Japan Chemical Week, 1991). In
India, 200-500 kg/day (60-150 tonnes per year) is manufactured
(Subrahmanyam et al., 1983). Production data from other countries are
not available.
It is estimated that elsewhere in the world around 1000 tonnes of
morpholine are produced annually.
3.2.1.3 Production processes
Three methods of producing morpholine have been described:
a) Reductive ammonation of diethylene glycol and hydrogen at a
pressure of 30-400 × 105 Pa and temperature of 150-400°C.
Possible catalysts include copper, nickel, cobalt, chromium,
molybdenum, manganese, platinum, palladium, rhodium and
ruthenium. Morpholine is recovered by fractional distillation
(Mjos, 1978).
b) Dehydration of diethanolamine with a strong acid such as oleum,
concentrated sulfuric acid or concentrated hydrochloric acid.
The acid is neutralized by the addition of an alkali to give the
free base of morpholine. Morpholine is recovered by extraction
using an organic solvent or concentrated aqueous alkali followed
by distillation (Mjos, 1978).
c) Heating bis(chloroethyl)ether and anhydrous ammonia in a closed
vessel to 50°C for 24 h. After venting the excess ammonia, the
product is filtered from ammonium chloride, and purified
morpholine obtained by distillation (Mjos, 1978).
BASF (Germany) uses method a in a continuous process in a closed
system, and the Texaco Chemical Company also uses method a. Hüls
(Germany) produced morpholine up to 1990 using method b (BUA, 1991).
Air Products and Chemicals use a low-pressure process in their plant
at Pace, Florida, USA (NRC, 1981).
3.2.1.4 Losses to the environment during normal production
A USA study on atmospheric morpholine releases was conducted by
Anderson (1983). No direct measurements were taken, and estimates of
morpholine emissions were based on analogy with emissions from
ethylene oxide production. Total annual emissions (process, storage
and fugitive emissions) from the processing to rubber accelerators (at
96 USA sites) and optical brighteners (at 128 USA sites) were
estimated at 5100 kg/year. Morpholine emission from miscellaneous
uses were estimated at an additional 900 kg/year (Anderson, 1983).
3.2.1.5 Methods of transport
Morpholine should be stored and transported in iron or steel
containers (Air Products and Chemicals, 1989).
3.2.1.6 Accidental release
There are no reports available on accidental releases of
morpholine.
3.2.2 Uses
Morpholine is an extremely versatile chemical. It is most
important as a chemical intermediate in the rubber industry, in
corrosion control, and in the synthesis of a large number of drugs,
crop protection agents, dyes and optical brighteners (Texaco, 1986;
Heilen et al., 1989). Morpholine is a solvent for a large variety of
organic materials, including resins, dyes and waxes (Texaco, 1986).
It can be used as a catalyst. Morpholine is still used in the USA in
toiletry and cosmetic products at concentrations up to 5% (Cosmetic
Ingredient Review, 1989). It is permitted for use in the USA in
several direct and indirect food additive applications.
The use pattern, which varies from country to country, is shown
in Table 3.
Approximately 33% of USA-produced morpholine is used as
intermediates for rubber accelerators and 25% as corrosion inhibitor
in steam boiler systems (Mjos, 1978). A high proportion (25-50%) of
the morpholine produced in Germany is used for optical brighteners in
detergent formulations. In Germany, morpholine-based vulcanization
auxiliaries are either imported or have been replaced by other
products. The use of about half of the morpholine produced in Germany
could not be identified (BUA, 1991).
3.2.2.1 Rubber chemicals
Morpholine derivatives are used in rubber vulcanization,
stabilization and the manufacture of special high-speed tyres.
Morpholine may be released during rubber processing (Mjos, 1978;
Heilen et al., 1989; BUA, 1991).
3.2.2.2 Anticorrosion agent
Morpholine has a volatility similar to water. It is therefore
widely used as a neutralizing amine in combating carbonic acid
corrosion in condensate return lines in steam boiler systems as well
as in aqueous hydraulic liquids and similar systems.
Table 3. Use pattern for morpholine (tonnes/year)
USA (1981)a Germany
(1988-90)b
Rubber chemicals 4920 (40%)
Corrosion inhibitors 3690 (30%) small amounts
Optical brighteners 615 (5%) 750-1500 (25-50%)
Alkyl morpholines 300-400 (10-13%)
Waxes and polishes 615 (5%) < 100 (< 3%)
Diazotype/blueprints 100 (3%)
Miscellaneous/no information 2460 (20%) < 900-1750 (30-60%)
a From: Mannsville Chemical Products (1981)
b From: BUA (1991)
Morpholine vapours protect silver and other metals against
corrosion and tarnish by acid fumes such as SO2 and H2S.
Corrosion of metal aerosol containers and valves can also be prevented
by the use of low levels of morpholine (Texaco, 1986). Morpholine is
effective in hydraulic system fluids based on glycols, where various
metals are in contact with the fluid at the same time (Brown, 1966).
Morpholine derivatives have been used as corrosion inhibitors in
mineral lubricating oil, turbine oils, for protecting storage tanks,
pipes and other devices used in handling petroleum distillates, and
for inhibiting the corrosive action of grease-proof paper on steel and
other metals (Texaco, 1986).
3.2.2.3 Waxes and polishes
Salts of morpholine with long-chain fatty acids, such as oleic or
stearic acid, have wax-like properties and are used as emulsifying
agents in the formulation of water-resistant waxes and polishes for
automobiles, floors, leather and furniture. When the loosely-bound
fatty acid-morpholine compound breaks down, the morpholine component
evaporates at approximately the same rate as water, leaving a film
highly resistant to water spotting and deterioration. Morpholine is
typically present in concentrations up to 2% (Texaco, 1986).
Morpholine is no longer employed in the production of waxes and
polishes in Germany (BUA,1991).
3.2.2.4 Optical brighteners
Optical brighteners are used in detergent formulations in the
soap and detergent industry. The diaminostilbene triazine type
brightener with morpholine as a substituent on one of the triazine
rings is particularly effective on cellulosics and is used in home
laundry detergents because it is stable to chlorine bleaches (Texaco,
1986).
3.2.2.5 Catalysts
Morpholine derivatives such as N-methylmorpholine and
N-ethylmorpholine are used as catalysts for the production of
polyurethane foams.
3.2.2.6 Pharmaceuticals
Morpholine derivatives are used as analgesics and local
anaesthetics (Texaco, 1986; Fisher, 1986; Rekka et al. 1990; Cusano &
Luciano, 1993), antibiotics (Kleemann & Engel, 1982; Schröder et al.
1982; BUA, 1991), antimycotics (Lauharanta, 1992; Reinel & Clarke,
1992) and for plaque control in dentistry (Collaert et al., 1992a,b).
3.2.2.7 Bactericides, fungicides and herbicides
Several morpholine derivatives, e.g., morpholinium salts of
certain acylated sulfonamides, possess bactericidal activity.
Morpholine hydroperiodide has been used as a water disinfectant
(Texaco, 1986).
Morpholine fungicides are used for agricultural purposes (Mercer,
1991), as foliar fungicides with protective and curative properties
for the control of powdery mildew and rust (Brouwers et al., 1992;
Leenheers et al. 1992), and as foliar fungicides for cereals
(Ackermann et al., 1989). Morpholine is also used in the preparation
of herbicides that can be applied either to the soil before the weeds
emerge or to the growing plants (Texaco, 1986).
3.2.2.8 Food additive applications
USA Federal regulations permit the use of morpholine in several
direct and indirect food additive applications (Cosmetic Ingredient
Review, 1989). Certain fatty acid salts of morpholine can be used as
components of protective coatings applied to fruits and vegetables
with the concentrations not allowed to exceed the level required to
produce the intended effect (US FDA, 1988). Indirect food additive
possibilities include the use of morpholine as a corrosion inhibitor
for steel and or tinplate used in food containers (US FDA, 1984a), as
a defoaming agent used in the manufacture of paper and paperboard for
food-packaging materials (US FDA, 1984b), as a component of adhesives
(US FDA, 1984c), and as a defoaming agent in animal glue used for
packaging materials (US FDA, 1984d). Morpholine is only allowed as a
boiler-water additive in concentrations up to 36 mg/m3 (10 ppm), but
is not permitted when the steam comes into contact with food, milk or
milk products (US FDA, 1984e).
In Germany, the use of morpholine in water-repellent food
packaging material is forbidden (BUA, 1991).
3.2.2.9 Cosmetics
Morpholine is used in the USA by the cosmetic industry. Data
submitted to the US Food and Drug Administration (US FDA) in 1981 and
1986 (Cosmetic Ingredient Review, 1989) and in 1991 (Cosmetic
Ingredient Review, 1991a) show that at least in the USA, morpholine is
still used in cosmetic products. In 1981, morpholine was used in 38
cosmetic preparations, the majority (32) being mascara. It is also
used in eyeliner, eye shadow and skin care preparations. Morpholine
is listed by the Cosmetic Ingredient Review as an ingredient used in
cosmetics, although there are insufficient data to substantiate safety
(Cosmetic Ingredient Review, 1989,1991a).
Morpholine is listed in Annex II of the EEC Cosmetics Directive.
Annex II lists compounds that must not be used in cosmetic
formulations. In Germany, the use of morpholine in cosmetic
preparations has been forbidden since 1985 (BUA, 1991) and in the EU
since 1986 (EEC, 1990).
Hydroxybenzomorpholine (HBM) is used as a colour additive for
hair dyes or colorants. In the FDA voluntary cosmetic registration
programme, it is listed as a component of 46 products.
Isostearamidopropyl morpholine lactate (IML), an antistatic agent
primarily used in hair conditioners and products, is present in five
reported cosmetic items. Quaternary morpholinium salts are given as
possible ingredients in hair conditioners and deodorants in wave
formulations (Mjos, 1978). The presence of morpholine as an
ingredient in shampoos has been reported (Spiegelhalder & Preussmann,
1984). However, a German survey in 1990 showed that morpholine was
not present in shampoos in Germany (BUA, 1991).
4. ENVIRONMENTAL TRANSPORT, DISTRIBUTION AND TRANSFORMATION
4.1 Transport and distribution between media
4.1.1 Volatilization
As morpholine is freely miscible with water, a Henry's constant
cannot be reliably calculated. However, estimates for this constant
(BUA, 1991) have been published. Donath et al. (1977) measured the
distribution coefficient (between vapour and liquid phase) for
morpholine as a function of temperature (50 to 130°C). They found that
the rate of volatilization was dependent on the concentration of
morpholine in the liquid phase. Extrapolation of their curve to 20°C
for morpholine concentrations of 10-15 mg per litre gives a value of
0.02, corresponding to a Henry constant value of 49 Pa.m3.mol-1.
Calculations from Bosholm (1983) give a value corresponding to
244 Pa.m3.mol-1.
According to the classification of Smith et al. (1980),
morpholine belongs to the group of "moderately volatile" substances.
4.2 Transformation
4.2.1 Biodegradation
Morpholine seems to be degraded only by a restricted range of
microbes, mostly Mycobacterium spp., which have specially adapted
(acclimated) themselves to this substrate under specific conditions
(Knapp et al., 1982; Cech et al., 1988; Knapp & Brown, 1988; Brown &
Knapp, 1990). Dmitrenko et al. (1985, 1987) identified an
Arthobacter sp. capable of doing this. Dmitrenko & Gvozdyak (1988)
reported the isolation of morpholine-degrading mycobacteria and found
that these organisms could utilize morpholine anaerobically with
nitrate as a terminal electron acceptor. Calamari et al. (1980) and
Tölgyessy et al. (1986) both reported the resistance of morpholine to
biodegradation. In addition, Tanaka et al. (1968) and Subrahmanyam et
al. (1983) both reported the failure of effluent treatment systems to
degrade morpholine.
Knapp & Brown (1988) isolated 13 morpholine-degrading bacterial
strains of Mycobacterium spp. in pure culture from their laboratory
activated sludge plant (ASP). They also found morpholine-degrading
bacteria in samples from a number of other habitats, including
activated sludge (from two sewage works), water from two rivers,
compost, soil and leaf litter. In all cases, there was a lag period of
10 to 20 days before degradation could be detected. The growth rate of
these morpholine-degrading strains is slow not only on morpholine but
also on other substrates.
Swain et al. (1991) studied the catabolic pathway for morpholine
when Mycobacterium strain MorG was grown with morpholine as sole
source of carbon and nitrogen. The results indicated that morpholine
is initially catabolized to 2-(2-aminoethoxy)acetate which can be
oxidatively cleaved to give rise to glycolate and indirectly to
ethanolamine. Mazure (1993) showed that morpholine can be degraded by
mixed cultures of gram-negative bacteria. Two mixed cultures were
studied, one containing 9 and the other 10 bacterial strains, mostly
pseudomonads. Interestingly, none of the individual strains was
capable of sustained growth with morpholine as a sole carbon and
nitrogen source. The rate at which the two mixed cultures degraded
morpholine was similar to that shown by Mycobacterium aurum in a
study by Cech et al. (1988).
Emtiazi (1993) reported that several Gram-negative bacteria
isolated as degraders of pyrrolidine and piperidine could oxidize
morpholine but could not grow on it as the sole source of carbon and
nitrogen. However, at least one strain could utilize morpholine as a
source of nitrogen if given succinate as a carbon source; the
degradation of morpholine was slower than that shown by mycobacteria.
4.2.1.1 Batch biodegradation tests
In several early studies all employing some form of biological
oxygen demand (BOD) test with unadapted inocula, morpholine was found
to be resistant to biodegradation (Swope & Kenna, 1950; Lamb &
Jenkins, 1952; Mills & Stack, 1953). However, Mills & Stack (1955) in
a later study utilized an inoculum adapted (for 116 days) to the
presence of morpholine and found that morpholine was degraded in a BOD
test after 4 days.
Strotmann et al. (1993) assessed the biodegradability of
morpholine using a test similar to that of the modified OECD Screening
Test (die-away test in an open system with low bacterial density)
(OECD guideline 301 E; OECD, 1981a,b). The inoculum used was taken
from an industrial sewage plant. As morpholine was regularly
discharged into this treatment plant, the inoculum was regarded as
adapted. An unadapted inoculum was obtained from a laboratory-scale
wastewater treatment plant operated with municipal wastewater. The
extent of degradation during the 28-day test (20°C incubation) was
determined by following the decrease in dissolved organic carbon
(DOC). The results showed that morpholine was degraded by both
adapted and unadapted inoculum. The lag period before start of
degradation was about 15 days for the adapted inoculum and 16 days for
the unadapted. The lag period given for the adapted cultures in this
study was rather long, especially considering the result of the
Zahn-Wellens test (below) carried out using the same inoculum. The
degradation period was 5 to 7 days for both unadapted and adapted
cultures. Under the conditions in this test, morpholine showed ready
biodegradability. The activated sludge concentration was about 30 mg
mixed liquor suspended solids (MLSS) per litre. Initial morpholine
concentration was 36 mg/litre.
A Zahn-Wellens Test (a test to estimate inherent
biodegradability) according to OECD guideline 302 B (OECD, 1981a,b)
was also performed by Strotmann et al. (1993). The adapted and
unadapted sludges were obtained as above, but the activated sludge
concentration was higher (1 g MLSS/litre). The concentration of
morpholine was about 725 mg/litre resulting in an initial DOC of
400 mg/litre; test duration was 31 days. Results showed that the lag
period with unadapted and adapted cultures was about 16-20 days and
7 days, respectively. In both cultures the extent of DOC removal was
more than 90% (morpholine was therefore rated as "inherently
biodegradable"). After the lag period, the maximum biodegradation
rates for adapted and unadapted activated sludges were
6 g morpholine/kg MLSS per h and 3 g morpholine/kg MLSS per h,
respectively. In this test the use of an adapted inoculum
significantly shortened the lag time. The authors suggested that this
effect, which was not observed in the modified OECD screening test,
might be due to the higher inoculum concentration used in the
Zahn-Wellens test.
4.2.1.2 Biodegradation in laboratory-scale wastewater treatment
plants
A laboratory-scale wastewater treatment plant operating with
municipal wastewater was supplemented with 4.5 to
5.0 mg morpholine/litre. More than 99% of the ammonia could be
eliminated by nitrification. The total organic carbon (TOC)
degradation ranged between 80 and 94%. The time taken for the sludge
to adapt to morpholine was 10 to 12 days. The adapted sludge of this
treatment plant was reported to be able to degrade morpholine for a
period of more than one month to more than 90% (Strotmann et al.,
1993)
In a die-away test (EEC, 1983), the kinetics of morpholine
biodegradation in the above treatment plant were determined (Strotmann
et al., 1993). At 20 h after adding 40 mg morpholine per litre, 65%
of the morpholine was degraded; after 25 h less than 10% of the added
morpholine was still present. In this adapted treatment plant, the
degradation occurred without any lag period, the maximum degradation
rate (3 g morpholine/kg MLSS per h) being reached after 18 h.
According to the authors, morpholine concentrations of 5 mg/litre in
wastewater can be well degraded in an adapted wastewater treatment
plant. However, shock loading with high concentrations (35 mg/litre)
can result in high concentrations of undegraded morpholine in the
effluent.
A model activated sludge plant capable of treating a simple
industrial waste influent (pH 5.4-5.6) containing morpholine, acetate
and salicylate and mineral salts was set up (Brown & Knapp, 1990).
The activated sludge was taken from the treatment plant of a
morpholine-containing effluent from a large chemical factory. It was
found that when morpholine was absent from the influent, the ability
of the activated sludge to degrade this compound was subsequently
reduced. This was shown by an increase in the lag period before
morpholine degradation could be detected in a die-away test from over
40 days, and was accounted for by a decline in the specific population
of morpholine-degrading microorganisms. The morpholine degradative
phenotype was shown to be genetically unstable in several pure
cultures of mycobacteria (Brown et al., 1990).
Since morpholine-degraders have a low growth rate, they can only
establish themselves in activated sludge if the Mean Solids Retention
Time (sludge age) is relatively long. Under semi-continuous
conditions (800 mg morpholine/litre), a sludge age of 8 days was
needed to achieve complete morpholine degradation (Cech & Chudoba,
1988).
In their investigations into morpholine-degrading bacteria in
river water from several different sites in Yorkshire, United Kingdom,
over a 3-month period, Knapp & Whytell (1990) found, as a general
trend, that the numbers of morpholine-degraders increased and die-away
lag times decreased as water passed downstream. This was probably
related to the cumulative polluting effects of discharges of effluent
to the rivers. The number of morpholine-degraders found in this
investigation agreed with similar studies from rivers in eastern
England. Of the 58 die-away tests carried out on 29 water samples,
only 3 (all from water classed as very clean) failed to reveal
morpholine biodegradation, although in several sites the numbers were
near the limits of detection (Knapp & Whytell, 1990).
4.2.2 Abiotic degradation
4.2.2.1 Hydrolytic degradation
Morpholine can thermally decompose at temperatures used in boiler
steam cycles. Agarwala (1982) found that, at 316°C, morpholine
decomposed in 12 h by 2-5% only, when used in boilers at 95 kg/cm2
and 108 kg/cm2, the decomposition products being ammonia and
carbonic acid products. Under the conditions found in steam-water
cycles in nuclear power plants (260°C and 4.55 MPa), ammonia,
methylamine, ethylamine, ethanolamine and 2-(2-aminoethoxy)ethanol
were identified as morpholine degradation products (Gilbert & Saheb,
1987; Lamarre et al., 1989).
Under normal field conditions, it is assumed that morpholine is
stable. However, no experimental data are available to confirm this.
4.2.2.2 Photochemical degradation
Amines react rapidly with hydroxyl radicals, and the irradiation
of amine-NOx mixtures in air results in the rapid conversion of NO
to NO2 and in the formation of ozone, carbonyls and other products
(Grosjean, 1991). The rate constant for the degradation of morpholine
in the atmosphere by hydroxyl radicals has not yet been measured
experimentally. Grosjean (1991) postulated a rate constant of
2-10 × 10-11 cm3.mol-1.sec-1 and gave a tentative reaction
scheme based on experimental data for dialkylamines.
Using the method of Atkinson (1988), a half-life (for morpholine)
of less than one day has been calculated (BUA, 1991).
As morpholine shows no absorption in the UV spectrum
(lambda > 260 nm), direct photochemical degradation in the atmosphere
or in the hydrosphere is unlikely (BUA, 1991).
4.2.2.3 Degradation by physico-chemical processes
Upon combustion in the presence of sufficient oxygen, carbon
monoxide, carbon dioxide and nitrogen gases are produced.
Combustion under oxygen-starved conditions can result in the
production of carbon monoxide, hydrogen cyanide, nitriles, cyanic
acid, isocyanates, cyanogens, nitrosamines, amides and carbamates
(Air Products and Chemicals, 1989).
4.2.3 Bioaccumulation
There are no data on the bioaccumulation of morpholine in aquatic
and terrestrial organisms. However, as the n-octanol/water
partition coefficient for morpholine is log Pow = -2.55 (at pH 7),
bioaccumulation is not expected (BUA, 1991).
4.3 Interaction with other physical, chemical or biological factors
Due to its carcinogenic properties the formation of NMOR from
morpholine has to be taken into account when assessing health and
environmental aspects of morpholine. NMOR can be formed by reaction
of aqueous solutions of nitrite with morpholine (Mirvish, 1975) or by
reaction of gaseous nitrogen oxides, e.g., N2O3, N2O4, NOx
in aqueous solutions of morpholine, even under normal environmental
conditions (Challis & Kyrtopoulos, 1979; Mirvish et al., 1988;
Schuster et al., 1990). Nitrogen oxide (NO) levels may be higher than
was previously thought (Cooney et al. 1992; Hibbs, 1992). The
conditions of nitrosation, in particular the pH, plays a significant
role.
In aqueous solutions, the reaction is as follows:
The rate of reaction of the nitrosation of morpholine by nitrite
is greatest at a pH value of 3.4, where the rate constant is
0.42 mol-2.s-1. An increase in the pH value has been shown to
result in a decrease in the rate of nitrosation with nitrite (Mirvish,
1975; Archer et al., 1977), and the rate was almost zero at pH > 7
(Archer et al., 1977).
In contrast, nitrosation with gaseous nitrogen oxides (N2O3,
N2O4, NOx) can take place over the whole pH range (Challis &
Kyrtopoulos, 1979; Meiners et al., 1980). Cooney et al. (1987) found
that, under certain conditions, the yield of NMOR at pH 7 was ten
times higher than at pH 2, but there was no further increase beyond
this pH.
Some nitrosamines, particularly alpha-nitrosamine aldehydes, are
potent transnitrosation reagents and are capable of nitrosating
morpholine at pH 7.9 (Loeppky et al., 1987).
Numerous reaction accelerators are known, e.g., thiocyanate
(Boyland et al., 1971), halides (Mirvish, 1975), formaldehyde (Archer
et al., 1977) and nitrosophenols, e.g., p-nitroso- o-cresol (Davies
et al., 1980). Enhancement of the nitrosation of morpholine by
nitrogen dioxide was reported in the presence of iodine (Challis &
Outram, 1979), vanillin and related phenols (Cooney & Ross, 1987) and
halides, particularly bromide (Cooney et al., 1987).
In contrast, the following compounds have been reported to
inhibit the nitrosation of morpholine almost completely: ascorbic acid
(Lathia & Schellhöh, 1981; Leach et al., 1991); urea or ammonium
sulfamate (Mirvish et al., 1972); gallic acid and sulfite (Mirvish,
1975); L-cysteine and DL-methionine ( in vitro study under
physiological conditions, Lathia & Edeler, 1989), catechol and
4-hydroxychavicol (Shenoy & Choughuley, 1989); alpha-tocopherol
(Norkus et al., 1986; Cooney et al., 1987; Schuster et al., 1990);
sulfhydryl compounds such as cysteine, cysteamine, glutathione and
thioglycolic acid, as well as extracts of onion and garlic juice
(Shenoy & Choughuley, 1992). Vitamin C, glucose, mannitol, cabbage
juice, orange juice, shiitake mushroom extract and saliva inhibited
the nitrosation of morpholine in vitro, but catechin, epicatechin
and tea extract enhanced the same reaction (Ohnishi, 1984). The
inhibitory effect of Chinese tea on the formation of NMOR in vitro
and in vivo has also been described (Wang & Wu, 1991).
Several C-nitro compounds, in particular tetranitromethane, have
been demonstrated to transnitrosate morpholine to form NMOR (Fan et
al., 1978). C-nitro compounds are widely used in industry as
pesticides, bactericides, colouring agents, drugs and perfumes.
Singer (1980) described the transnitrosation of morpholine with
nitrosamines and nitrosureas under acid conditions in the presence of
thiocyanate. These reactions are dependent on the pH value and steric
and electronic factors, as well as on the basicity of the amines. In a
model study, the nitrosation of morpholine by nitro-nitroso compounds,
such as those found in fried bacon, was observed (Liu et al., 1988).
NMOR can be formed in vivo in humans and has been found in
various tissues and fluids such as human saliva (Boyland et al., 1971;
Wishnok & Tannenbaum, 1977) and human gastric juice (Ziebarth, 1973;
1974; Sen & Baddoo, 1989; Yurchenko et al., 1990). NMOR formation has
been reported in rat lungs (Postlethwait & Mustafa, 1983), whole mice
(Iqbal et al. 1980; Norkus et al. 1984), stomach (Furman & Rubenchik,
1991), hepatocytes isolated from woodchucks (Marmota monax) (Liu et
al., 1992) and microorganisms (Archer et al., 1979; O'Donnell et al.,
1988; Calmels et al., 1991a,b). Bacterial catalysis of
N-nitrosation of morpholine has been reported in a range of bacteria
often isolated from the human gut or urinary tract infections (Suzuki
& Mitsuoka, 1984; Calmels et al., 1987, 1988; Mackerness et al.,
1989), including the ubiquitous gut bacterium Escherichia coli and
Pseudomonas aeruginosa, which is also widespread in the aquatic
environment. Bacterial catalysis of N-nitrosation of morpholine is
heat labile and is optimal at neutral to slightly alkaline pH (Calmels
et al., 1985; Leach et al., 1987). N-nitrosation by bacteria is
generally associated with the ability to reduce nitrate. It appears
that those that reduce nitrate to nitrogen or nitrogen oxides (e.g.,
P. aeruginosa) can nitrosate at much greater rates than those (e.g.,
E. coli) that only reduce nitrate to nitrite (Leach et al.,1987;
Calmels et al., 1988). There is considerable variation between
strains of the same species. Bacterial N-nitrosation of morpholine
has been shown to follow Michaelis-Menten kinetics (Calmels et al.,
1985; Leach et al., 1987). E. coli A10, for example, displays Km
values of 7.4 mmol/litre for morpholine and 11.4 mmol/litre for sodium
nitrite. It has been shown that the rate of bacterial N-nitrosation
of secondary amines is inversely related to the pKa of the amine
(Calmels et al., 1985; Leach et al., 1987, 1991), with a linear
relationship between log10 of the rate of nitrosation and pKa.
Morpholine, having a relatively low pKa, is thus relatively
susceptible to nitrosation compared, for example, to alkyl amines.
It has been shown that ascorbate is capable of inhibiting
nitrosation of morpholine by P. aeruginosa (Leach et al., 1991).
Although most nitrosation studies have used whole bacteria, an enzyme
catalyzing N-nitrosation of morpholine has been isolated and
purified from two denitrifying bacteria (Calmels at al., 1990).
4.4 Ultimate fate following use
4.4.1 Fate of morpholine in various products
Morpholine is an important industrial chemical with a wide range
of applications (see section 3.2.2) and therefore may be present in
many industrial emissions.
Its use as a corrosion inhibitor in boiler water means that
morpholine and its decomposition products will be found in boiler
wastewater, including water from power plants using morpholine. In a
study by McCain & Peck (1976), morpholine concentrations in the
discharge streams of three Hawaiian power plants ranged from not
detectable to 0.008 mg/litre, suggesting that the potential for human
exposure is small.
Its use in the manufacture of rubber additives results in an
indefinable amount of morpholine being released into the hydrosphere
or geosphere not only during manufacturing processes but also through
tyre abrasion and disposal of used tyres.
Morpholine is released during vulcanization processes using
morpholine-containing accelerators such as 2-( N-morpholino-
thio)benzothiazole (MBS) (Badura et al., 1989). Some of the amine is
released into the atmosphere and some is bound to the rubber. Even
the accelerator itself can contain free amine. The morpholine content
of MBS is < 0.4% by weight. This level can be higher if the
accelerator is not stored properly and is exposed to heat or moisture
(BUA, 1991).
Aarts et al. (1990) detected free volatile morpholine at
concentrations of between 70 (new) and 230 mg/kg (old) in samples of
dithio-bis-morpholine (DTBM). After extraction in water for one hour
in an ultrasonic bath, ten times this amount was detected, i.e.
960 mg/kg in newly made and 2750 mg/kg in stored DTBM. These
quantities of amine could be released during vulcanization.
Optical brighteners adhere to clothes during the first wash but
tend to be released into the wastewater in subsequent washings.
Although these substances are not themselves biologically degradable,
they have been found to disappear from wastewater after a two-step
biological treatment presumably due to the high rate of adsorption to
the sludge particles (Jakobi et al., 1983).
As mentioned in section 3.2.2, morpholine is released into the
environment by volatilization through its use in waxes and polishes
(Texaco, 1986).
4.4.2 Waste disposal
Controlled incineration is the preferred method of disposal
(Sittig, 1985; Air Products and Chemicals, 1989). The incinerator
should be equipped with a scrubber or thermal unit. Nitrogen oxide
emissions should meet environmental regulations.
5. ENVIRONMENTAL LEVELS AND HUMAN EXPOSURE
5.1 Environmental levels
5.1.1 Ambient air
No data are available on levels of morpholine in ambient air.
5.1.2 Water
5.1.2.1 River water
Since mid-1990, the levels of morpholine in some rivers in North
Rhine-Westphalia, Germany, have been monitored (BUA, 1991). No
morpholine could be detected at three different points in the River
Rhine or in five of its tributaries (detection limit, 5 µg/litre). No
morpholine was found in samples of Tennessee freshwater (detection
limit, 0.07 µg/litre) (Singer & Lijinsky, 1976a). In 1979, 33 water
samples were collected at 11 sites in Japan, but no morpholine could
be detected (detection limit, 1-5 µg/litre) in any of the samples
(Environment Agency Japan, 1980).
5.1.2.2 Wastewater
There are no data on morpholine levels in wastewater.
A single sample of wastewater from a tyre chemical factory in
Ohio, USA was found to contain 3 µg NMOR/litre (Fajen et al., 1979).
In England, samples were taken from the inlets and outlets of
four sewage treatment plants (Richardson et al., 1980). NMOR
(100 µg/litre) was found only in the outlet of a cutting-fluid
recovery plant.
5.1.3 Sediment
Spies et al. (1987) examined contaminated sediments in San
Francisco Bay, USA and found several benzothiazoles, including
2-(4-morpholinyl)-benzothiazole, which is present as an impurity in
commercial 2-(morpholinothio)-benzothiazole used in motor tyres. The
authors carried out weathering tests on this latter commercial
substance and found that the morpholine impurity was environmentally
stable. They suggested that the 2-(4-morpholinyl)-benzothiazole found
in the sediments (up to 0.36 mg/kg dry weight) was a result of
accumulated street run-off. Morpholine itself could not be detected.
In 1979, 33 bottom sediment samples were collected at 11 sites in
Japan, but no morpholine could be detected (detection limit,
0.01-0.5 mg/kg) in any of the samples (Environment Agency Japan,
1980).
5.1.4 Soil
There are no data on the presence of morpholine in soil.
2-(4-Morpholinyl)-benzothiaozole (273 µg/kg dry weight) was detected
1.6 km from a motorway in California, USA (Spies et al., 1987) (see
also section 5.1.2).
NMOR (4.4 mg/kg) was detected in a single sample of soil near to
a tyre chemical factory in Ohio, USA (Fajen et al., 1979).
5.1.5 Terrestrial and aquatic organisms
Levels of morpholine found in single or small samples of fish are
given in Table 6, but the sample numbers are too low to make an
evaluation. No other data are available.
5.2 General population exposure
5.2.1 Indoor air
No data on indoor air exposure to morpholine are available.
Analysis for NMOR in the air inside new cars showed levels of up
to 2.5 µg/m3. Levels were 4 to 10 times lower when the air-venting
system was working, indicating that NMOR exposure is limited to the
first few minutes of each trip (Rounbehler et al., 1980). During a
simulation of conditions inside cars on a hot day, concentrations of
up to 0.4 µg NMOR/m3 were measured at 60°C (Dropkin, 1985).
5.2.2 Drinking-water and food
There are no data on the morpholine content of drinking-water.
Food can become contaminated with morpholine in several ways:
(a) through direct treatment of fruit with waxes containing morpholine
for conservation purposes; (b) by use of packaging material
containing morpholine, and (c) through steam treatment during
processing.
Ohnishi et al. (1983) found morpholine at concentrations of
< 71.1 mg/kg in the peel of retail citrus fruits in Japan. In the
pulp (flesh) of the fruits the level was much lower, being less than
0.7 mg/kg (Table 4). Marmalade made from whole fruits contained
concentrations of morpholine between 0.3 to 0.7 mg/kg. If the fruits
were previously washed in washing-up liquid, morpholine concentrations
were reduced, but only by 25%. Even if the fruit was boiled for
20 minutes, a third to a quarter of the morpholine still remained. The
morpholine removed by these processes could be detected quantitatively
in the washing and boiling water (Ohnishi et al., 1983).
Table 4. Morpholine content of citrus fruits and marmalade from
citrus fruitsa
Sample Number Morpholine
(mg/kg)b
Orange (variety a)c peel 12
n.d.-57.0
fruit pulp 3 0.2-0.7
Orange (variety b)c peel 6 5.0-71.1
fruit pulp 1 0.3
Mandarine peel 2 16.1-18.0
fruit pulp 1 n.d.
Lemon peel 2 n.d.-5.2
fruit pulp 1 n.d.
Grapefruit peel 2 2.8-7.0
fruit pulp 1 n.d.
Marmalade from citrus fruits 4 0.3-0.7
a adapted from Ohnishi et al. (1983)
b n.d. = not detectable (detection level 0.2 mg/kg),
presumably fresh weight
c variety not specified
Sen & Baddoo (1989) reported the morpholine and NMOR content of
waxed and unwaxed apples of Canadian origin, obtained either direct
from the packers or from retail sources. Liquid wax spray is used as
a protective coating on fruit and vegetables to reduce moisture loss
and thereby extend the shelf-life of the product. Apple homogenates
and liquid waxes were analysed for their morpholine contents
(Table 5). Although the concentrations of morpholine found in waxed
apples were high, NMOR could not be found in any of the waxed or
unwaxed samples. Low levels of morpholine in the unwaxed apples could
be due to contamination during packing or transport.
Singer & Lijinski (1976a) analysed a variety of foodstuffs for
the presence of morpholine but the sample size was too small to draw
any conclusions. The results are given in Table 6. The sources of
contamination with morpholine are in these cases not clear. The
possibility of artifacts is unlikely according to the authors.
Table 5. Concentration of morpholine and NMOR (mg/kg) in samples of
liquid waxes and waxed and unwaxed applesa
Liquid wax Unwaxed apples Waxed apples
NMOR morpholine NMOR morpholine NMOR morpholine
0.286 27 300 n.d. n.d. n.d. 4.3
0.668 31 500 n.d. 0.118 n.d. 4.9
0.138 24 400 n.d. 0.016 n.d. 6.3
0.277 38 500 n.d. 0.041 n.d. 7.1
0.152 22 500 n.d. n.d. n.d. 4.0
0.585 33 300 n.d. 0.018 n.d. 7.7
a adapted from Sen & Baddoo (1989); n.d. = not detected (detection
limit: 0.005 mg/kg for morpholine, 0.0005 mg/kg for NMOR)
Table 7 summarizes the results of investigations into the
concentrations of morpholine and NMOR in prepacked milk products
(Hoffmann et al., 1982). The values range from 5-77 µg/kg for
morpholine and "not detectable" to 3.3 µg/kg for NMOR. Contamination
of prepacked foodstuffs with morpholine might be explained by the use
of morpholine in steam boiler systems for paper and cardboard
production.
Hotchkiss & Vecchio (1983) found morpholine concentrations of
between 0.098 and 8.4 mg/kg (mean 0.38 mg/kg) in food packaging. A
sample of flour nearest the wall of the paper bag contained 1.1 µg
NMOR/kg. The bag itself contained 33.0 µg NMOR/kg. In an experimental