Published under the joint sponsorship of the United Nations Environment Programme, the International Labour Organization, and the World Health Organization, and produced within the framework of the Inter-Organization Programme for the Sound Management of Chemicals.
World Health Organization Geneva, 2000
The International Programme on Chemical Safety (IPCS), established in 1980, is a joint venture of the United Nations Environment Programme (UNEP), the International Labour Organization (ILO), and the World Health Organization (WHO). The overall objectives of the IPCS are to establish the scientific basis for assessment of the risk to human health and the environment from exposure to chemicals, through international peer-review processes, as a prerequisite for the promotion of chemical safety, and to provide technical assistance in strengthening national capacities for the sound management of chemicals.
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Environmental Health Criteria
PREAMBLE
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IPCS TASK GROUP ON ENVIRONMENTAL HEALTH CRITERIA FOR dinitro-ortho-cresol
Members
Dr D. Anderson, British Industrial Biological Research Association (BIBRA) International, Carshalton, Surrey, United Kingdom
Dr B.H. Chen, Department of Environmental Health, School of Public Health, Shanghai Medical University, Shanghai, People’s Republic of China
Dr S. Dobson, The Institute of Terrestrial Ecology, Monks Wood Experimental Station, Abbots Ripton, Huntingdon, Cambridgeshire, United Kingdom
Professor M.C.A. Lotti, Università degli Studi di Padova, Istituto di Medicina del Lavoro, Azienda Ospedaliera, Padova, Italy (Chairman)
Dr P. Lundberg, Risk Evaluation Group, Department of Occupational Medicine, National Institute for Working Life, Solna, Sweden
Dr L.R. Papa, National Center for Environmental Assessment – CIN, US Environmental Protection Agency, Cincinnati, Ohio, USA
Dr A.F. Pelfrène, The Agrochemicals Defense Network, La Marjolaine, Charbonnières-les-Bains, France (Rapporteur)
Professor S.A. Soliman, Department of Pesticide Chemistry, Faculty of Agriculture, Alexandria University, El-Shatby, Alexandria, Egypt
Secretariat
Mr Y. Hayashi, Scientist, International Programme on Chemical Safety, World Health Organization, Geneva, Switzerland
Dr Y. Uyama, Food Chemistry Division, Environmental Health Bureau, Ministry of Health and Welfare, Tokyo, Japan (On secondment to the International Programme on Chemical Safety)
Dr M. Younes, Acting Coordinator, International Programme on Chemical Safety, World Health Organization, Geneva, Switzerland (Secretary)
WHO TASK GROUP ON ENVIRONMENTAL HEALTH CRITERIA FOR DINITRO-ortho-CRESOL
A WHO Task Group on Environmental Health Criteria for Dinitro-ortho-cresol was held at the World Health Organization, Geneva, Switzerland from 20 to 23 April 1999. Dr R. Helmer, Director, Department for the Protection of the Human Environment, opened the meeting and welcomed the participants on behalf the IPCS and its three cooperating organizations (UNEP/ILO/WHO). The Task Group reviewed and revised the draft criteria monograph and made an evaluation of the risks for human health and the environment from exposure to dinitro-ortho-cresol.
Dr A.F. Pelfrène prepared the first draft of this monograph. The second draft incorporated comments received following the circulation of the first draft to the IPCS Contact Points for Environmental Health Criteria monographs.
Dr B.H. Chen (IPCS) and Ms K. Lyle (Sheffield, England) were responsible for the overall scientific content and technical editing, respectively.
The efforts of all who helped in the preparation and finalization of the monograph are gratefully acknowledged.
* * *
Financial support for this Task Group was provided by the US Food and Drug Administration as part of its contributions to the IPCS.
ABBREVIATIONS
| 4-ANOC | 4-amino-6-nitro-o-cresol |
| 6-ANOC | 6-amino-4-nitro-o-cresol |
| 6-Ac ANOC | 6-acetamido-4-nitro-o-cresol |
| ADI | acceptable daily intake |
| ADP | adenosine disphosphate |
| AdSV | adsorptive stripping voltametric detector |
| a.i. | active ingredient |
| ALT | alanine aminotrasferase |
| 3-ANSA | 3-amino-5-nitrosalicyclic acid |
| AST | aspartate aminotransferase |
| ATP | adenosine triphosphate |
| b.w. | body weight |
| BMR | basal metabolic rate |
| BOEL | biological operation exposure limit |
| BSI | British Standards Institute |
| CA | Chemical Abstracts |
| CAS | Chemical Abstracts Services |
| DECOS | Dutch Expert Committee on Occupational Standards |
| DNC | synonym for DNOC |
| DNHMP | 4,6-dinitro-2-hydroxymethylphenol |
| DNOC | 4,6 dinitro-o-cresol |
| DPP | differential pulse polarographic detector |
| DT50 | median degradation time |
| EC | emulsifiable concentrate |
| EC50 | median effective concentration |
| ELCD | electrochemical detector |
| ENT 154 | synonym for DNOC |
| EPPO | European and Mediterranean Plant Protection Organization |
| FID | flame ionization detection |
| F0 | first filial generation |
| GC | gas chromatography |
| GLP | Good Laboratory Practice |
| GTZ | German Agency for Technical Cooperation |
| HPLC | high-performance liquid chromatography |
| HRGC | high-resolution gas chromatography |
| ISO | International Organization for Standardization |
| IUPAC | International Union of Pure and Applied Chemistry |
| JMAF | Japanese Ministry of Agriculture and Forestry |
| JMPR | FAO/WHO Joint Meeting on Pesticide Residues |
| LC50 | median lethal concentration |
| LC–MS | liquid chromatography–mass spectrometry |
| LD50 | median lethal dose |
| MACWZ | maximum allowable concentration in the working zone |
| MRL | maximum residue limit |
| MS | mass spectrometry |
| MS–MS | tandem mass spectrometry |
| MTD | maximum tolerated dose |
| NOAEL | no observed adverse effect level |
| NOEC | no observed effect concentration |
| NOEL | no effect level |
| NPD | nitrogen phosphorus detector |
| OECD | Organisation for Economic Co-operation and Development |
| OL | oil-miscible liquids |
| PA | Pastes |
| PDD | photodiode array detector |
| PND | phosphorus/nitrogen detector |
| PT50 | median photolysis time |
| RSD | relative standard deviation |
| SC | suspension concentrate |
| SGOT | see ALT |
| SGPT | see AST |
| SPE | solid phase extraction |
| SPME | solid phase microextraction |
| t½ | half-life |
| T3 | Triiodothyronine |
| T4 | Thyroxine |
| JMPR | FAO/WHO Joint Meeting on Pesticide Residues |
| TER | toxicity exposure ratio |
| TSELhm | tentatively safe exposure level in the atmosphere of residential areas |
| TWA | time weighted average |
| UV | Ultraviolet |
| v/v | volume per volume |
The solubility of DNOC in water is 6.94 g/litre at 20 °C and pH 7, and largely depends on pH.
DNOC is relatively stable in sterile water.
DNOC is analysed in environmental media by high-performance liqid chromatrography (HPLC) with ultraviolet (UV) detection or by gas chromatography (GC) with detection by nitrogen phosphorus dection (NPD), flame ionization detection (FID) or mass spectrometry (MS). In biological fluids, determination of DNOC is usually by spectrophotometry and more recently by either GC/NPD or HPLC/UV.
Occupational exposure is expected to occur in agriculture and in the chemical industry.
DNOC did not induce any teratogenic effects in pregnant rats receiving oral doses up to 25 mg/kg b.w. per day from gestation day 6 to day 15, inclusive. In rabbits, treated orally, the high dose of 25 mg/kg b.w. per day was maternally toxic, inducing mortality. At this dose level teratogenic effects, including microphthalmia or anophthalmia and hydrocephaly or microcephaly, were observed.
When administered to pregnant rabbits by cutaneous application during gestation, DNOC induced maternal toxicity at the high dose of 90 mg/kg b.w. per day, resulting in some embryotoxicity but not teratogenicity. No evidence of teratogenicity or embryotoxicity was recorded in mice treated orally or intraperitoneally during pregnancy.
DNOC is acutely toxic to honey bees but exposure is likely to be low; hazard quotients for honey bees indicate low risk. TER for earthworms (LC50 at 17 mg/kg soil) indicates moderate risk following use of DNOC as a desiccant.
The high acute toxicity of DNOC for birds and mammals is unlikely to be manifest in the environment because exposure is likely to be low. This conclusion is supported by limited reports of incidents in the field. Further characterization of risk is not possible because field information on residues and effects is not available.
Given the present use patterns of the plant protection product containing DNOC as the active ingredient, there are no detectable residues in treated crops, and thus no exposure of the general population.
DNOC is a skin sensitizer in guinea-pigs.
Agricultural use as a desiccant and on dormant fruit crops leads to calculated risk factors indicating possible adverse effects on aquatic organisms (from spray drift) and earthworms. Other organisms in the field are unlikely to be adversely affected because exposure will be low. No risk assessment was attempted for possible other uses of DNOC (such as locust control) because of lack of information on application rates and methods.
Chemical structure:
| Relative molecular mass: | 198.13 |
| Common name: | DNOC (ISO, WSSA, BSI, JMAF) |
| Chemical names: | 4,6-dinitro-ortho-cresol
(IUPAC)
2-methyl-4,6-dinitrophenol (CA) 2,4-dinitro-ortho-cresol 3,5-dinitro-2-hydroxytoluene 2,4-dinitro-6-methylphenol |
| Synonyms: | DNC; ENT 154 |
| Common trade names: | Antinonin; Bonitol; Dinitrol; Technolor; Trifocide; Trifina; Veraline |
| Trade names no longer in use: | Elgetol; Extar A; Nicyl; Nitrador; Sandoline; Selinon; Sinox |
| CAS registry number: | |
| CIPAC number: | 19 |
| EEC number: | 208 601 1 |
| UN number: | 1598 |
Table 1. Physical and chemical properties of DNOC
| Property | Characteristics | Reference |
| Physical state | yellow, crystalline, solid | Jongerius & Jongeneelen (1991) |
| Crystal structure | Triclinic | Jongerius & Jongeneelen (1991) |
| Purity of the technical product | 97.45%
95–98% |
Sainsbury et al. (1995)
Tomlin (1997) |
| Molecular weight | 198.13 | Tomlin (1997) |
| Melting point | 88.2–89.8 °C | Hope et al. (1995) |
| Boiling point | 312 C | Jongerius & Jongeneelen (1991) |
| Vapour pressure | 1.6 × 10–2 Pa at 25 ° C | Howarth et al. (1995) |
| Relative density | 1.58 at 20 ° C | Hope et al. (1995) |
| Solubility in water (20 ° C) | 0.214 g/litre at pH 4
6.94 g/litre at pH 7 33.3 g/litre at pH 10 |
Hope et al. (1995) |
| Solubility in organic solvents (at 20 ° C) | Hope et al. (1995), Tomlin (1997) | |
| toluene | 251 g/litre | |
| methanol | 58.4 g/litre | |
| dichloromethane | 503 g/l | |
| acetone | 514 g/litre | |
| hexane | 4.03 g/litre | |
| log Pow | 1.78 at pH 4
8.67 × 10–2 at pH 7 |
Hope et al. (1995) |
| Dissociation constant (pKa) | 4.48 at 20 ° C
4.9 and pH limits 3–8.5 |
Hope et al. (1995)
Heimlich & Nolte (1993) |
| Vapour density | 6.84 (air = 1) | Jongerius & Jongeneelen (1991) |
| Saturation vapour concentration (20–25 ° C) | 0.56–1.0 mg/m3 | Jongerius & Jongeneelen (1991) |
| Conversion factor
(at 760 mmHg and 20 ° C) |
1 mg/m3 = 0.12 ppm
1 ppm = 8.24 mg/m3 |
Jongerius & Jongeneelen (1991) |
| Flammability | no auto-ignition below 400 ° C | Tremain & Bartlett (1995) |
| Stability in water | DT50 >1 year | Tomlin (1997) |
| Photolysis | PT50 _ 253 h (20 ° C) | Tomlin (1997) |
Like all other dinitrophenols, DNOC is a pseudoacid and readily forms water-soluble salts with alkalis (Metcalf, 1978; HSDB, 1994). At pH 4.4, more than 50% of the DNOC in water exists as the free anion. The concentration of DNOC in ionized form increases as the pH increases, and at pH 7 or above 100% of DNOC will be in the ionized form. Therefore, at physiological pH DNOC is either ionized or bound to macromolecules (i.e., albumin) (King & Harvey, 1953b).
Levels of DNOC in environmental and biological samples can be measured following several extraction or clean-up steps. These steps might include liquid–liquid extraction, solid phase extraction or solid phase microextraction. Both HPLC and GC with several detection methods are used for final separation and quantification.
All analytical methods used for measuring DNOC in biological samples listed in Table 3 rely on spectrophotometry for final quantification, with the exception of those of Hopper et al. (1992) and Diepenhorst et al. (1995). False positive results may be obtained by these methods because of abnormally high bilirubin or carotene levels in the blood (Jongerius & Jongeleenen, 1991).
Table 2. Analytical methods for measuring DNOC in environmental samples
| Type of sample | Preparation | Analytical method | Detection limit | Recovery (%) | Reference |
| Technical and formulated products | Dissolve sample in methanol or acetone | HPLC/UV | 2 nga | No data | Farrington et al. (1982); Yao et al. (1991) |
| Technical products | Dissolve sample in methanol | HPLC/ELCD | 0.1 nga
(oxidative) 0.4 nga (reductive) |
No data | Yao et al. (1991) |
| Air | Draw air through filter and a midget bubbler in series. DNOC extracted into ethylene glycol and 2-propanol added before analysis | HPLC/UV (method S166) | 0.070 mg/m3 (8 ppb) for 180-litre sample | 104 for 0.07 mg loaded on to filter | NIOSH (1984) |
| Water | Sample adjusted to pH 6.1 by buffer | HPLC/AdSV
HPLC/DPP |
0.1 µg/litre (AdSV)
1.5 µg/litre (DPP) |
No data | Benadikova & Kalvoda, (1984) |
| Water | Extract reconstituted in methanol-acetonitrile acetic acid (20:78.5:1.5 v/v) | HPLC/UV | No data | 97 | Tripathi et al. (1989) |
| Drinking-water, atmospheric water | Acidify sample, add salt, and extract continuously with methylene chloride. Dry, reduce volume, and solvent exchange to hexane. Derivatize with acetic anhydride | GC/NPD | 0.20 µg/litre
(0.2 ppm) |
102 (5.5% RSD) | Herterich (1991) |
| Drinking-water, groundwater | Acidify water, add sodium sulfite, and pass through SPE cartridge of Carbopak. Elute with methanol/ methylene chloride; reduce volume | HPLC/UV | 0.009 µg/litre
(9 ppb) |
96 | Di Corcia & Marchetti (1992) |
| Groundwater | Acidify to pH 2, saturate with salt, and extract using SPME | GC/MS | 0.070 µg/litre (0.07 ppm) (5.6% RSD) | No data | Buchholz & Pawliszyn (1993) |
| Groundwater, sediment | Extract acidified water with methylene chloride, reduce volume and solvent exchange to 2-propanol | GC/FID
(Method 8040) |
160 µg/litre | 0.84C – 1.01 where C is the true value of concentration in µg/litre | US EPA (1986a) |
| Groundwater, soil, solid waste | Extract acidified water with methylene chloride, reduce volume and exchange into 2-propanol. For other matrices, mix with anhydrous sodium sulfate and extract (soxhlet or sonication) with methylene chloride. Reduce volume. Clean up with silica gel if needed | GC/MS
(Method 8270) |
50 µg/litre
(50 ppm water); 3.3 mg/kg (ppm soil/ sediment) |
1.04C – 28.04 where C is the true value of concentration in µg/litre | US EPA (1986b) |
| Waste water | Extract acidified sample with methylene chloride; concentrate and exchange solvent to 2-propanol | GC/FID
(Method 604) |
16 µg/litre
(16 ppm) |
83 at 100 µg/litre | US EPA (1984a) |
| Waste water | Extract acidified sample with methylene chloride; concentrate | GC/MS
(Method 625) |
24 µg/litre
(24 ppm) |
93 at 100 µg/litre | US EPA (1984b) |
| Waste water | Extract acidified sample with methylene chloride, dry and reduce volume. Add deuterated standards | GC/MS isotope dilution
(Method 1625) |
20 µg/litre
(20 ppm) |
77–133 at 100 µg/litre | US EPA (1984c) |
| Rain and snow | Extract acidified sample with methylene chloride; concentrate | HPLC/PDD | No data | No data | Alber et al. (1989) |
| Soil | Extract with methylene chloride; evaporate to dryness and dissolve residue in alkaline methanol/water | HPLC/UV | 0.005 mg/kg
(5 ppb) |
85–105 | Roseboom et al. (1981) |
| Soil | Soxhlet extraction of clay loam using hexane : acetone (1 : 1). Reduce volume | GC/MS | No data | 63.4 at 6 mg/kg | Lopez-Avila et al. (1993) |
| Various crops | Extract macerated or homogenized sample with methylene chloride; evaporate to dryness and dissolve in potassium carbonate/methanol mixture | HPLC/UV | 0.005 mg/kg
(5 ppb) |
82–105 at 0.05 mg/kg
%RSD range 4–13% |
Roseboom et al. (1981) |
| Various crops | Homogenize sample in blender, adding distilled water as needed. Add Florisil to form free flowing mixture and pack into a column with a sodium sulfate layer at bottom. Elute with methylene chloride : acetone (1 : 1) or ethyl acetate. Reduce volume | GC/ELCD | 0.001 mg/kg
(1 ppb) |
69–79 at 0.01–0.5 mg/kg | Kadenczki et al. (1992) |
| Fatty and non-fat foods | Mix fatty sample with methanol, sulfuric acid and potassium oxalate and, non-fat samples with sulfuric acid and methanol; extract both with petroleum ether or methylene chloride; clean-up by gel permeation chromatography, methylate and clean up with Florisil | GC/NPD | No data | 45–50 (fatty foods)
>80 (non-fat foods) |
Hopper et al. (1992) |
aThere are absolute detection limits.
AdSV, adsorptive stripping voltametric detector; DPP, differential pulse polarographic detector; ELCD, electrochemical detector; FID, flame ionization detection; GC, gas chromatography, HPLC, high-performance liquid chromatography; HRGC, high-resolution gas chromatography; MS, mass spectometry; NPD, nitrogen phosphorus detector; PDD, photodiode array detector; RSD, relative standard deviation; SPE, solid phase extraction; SPME, solid phase microextraction; UV, ultraviolet detector; v/v, volume per volume.
Table 3. Analytical methods for measuring DNOC in biological samples
|
Sample matrix |
Preparation method |
Analytical method |
Sample detection limit |
Recovery (%) |
Reference |
|
Animal tissue |
Extract sample mixed with methanol, sulfuric acid, and potassium oxalate with petroleum ether; clean up by gel permeation chromatography, methylate, and clean up with Florisil |
GC-NPD |
No data |
45–50 |
Hopper et al. (1992) |
|
Urine, kidney, liver, brain (DNOC and metabolite 4-amino-2-methyl-6-nitrophenol) |
Hydrolyse sample directly or after acetone extraction; extract with petroleum ether |
Spectrophotometric |
No data |
No data |
Truhaut & de Lavaur (1967) |
|
Serum |
Dilute with water; add sodium chloride and sodium carbonate and extract with methyl ethyl ketone |
Spectrophotometric |
<0.5 mg/litre |
No data |
Parker (1949) |
|
Serum |
Samples were acid coagulated then serum separated by centrifugation |
HPLC/UV |
0.05 m g/g |
91.0 |
Diepenhorst et al. (1995) |
|
Tissue |
Dilute homogenized tissue with water; add sodium chloride and sodium carbonate; extract with methyl ethyl ketone |
Spectrophotometric |
No data |
No data |
Parker (1949) |
|
Urine (DNOC and metabolite 4-amino-2-methyl-6-nitrophenol) |
Acidify and subject to continuous extraction with diethyl ether |
Spectrophotometric |
No data |
No data |
Smith et al. (1953) |
|
Urine |
Add sodium chloride and sodium carbonate; extract with methyl ethyl ketone |
Spectrophotometric |
No data |
No data |
Parker (1949) |
GC, gas chromatography; NPD, nitrogen phosphorus detection device.
DNOC is also used as a desiccant in potatoes. It is sprayed once or twice on seed potatoes between July and September to desiccate the haulms in order to prevent virus and disease contamination of the tubers, and incidentally to facilitate mechanical harvesting. The registered rates of application of DNOC range from 2.5 to 5.6 kg/ha.
DNOC is formulated as emulsifiable concentrate (EC) for use as a potato haulm desiccant and as a suspension concentrate (SC) for winter treatment on fruit trees. Other types of formulation include pastes (PA) and oil-miscible liquids (OL). It is understood that DNOC is still used as a desiccant for crop potatoes and in locust control in developing countries. However, details of sources, application rates and methods are not available.
Although the use of DNOC as a pesticide has currently declined, and also because it has been banned in some countries (see for instance EC, 1999), there are still significant volumes of obsolete stocks of this chemical around the world, especially in developing countries. The German Agency for Technical Cooperation (GTZ) has helped in disposing of 57.6 tonnes of DNOC in the United Republic of Tanzania by incineration in a cement kiln (GTZ, 1997). More than 14 tonnes of obsolete DNOC have been located in Zambia (Wodageneh, 1997).
The main current use of DNOC is in the plastics industry as an inhibitor of polymerization in styrene and vinyl aromatic compounds. It is also used as an intermediate for synthesis of other fungicides, dyes and pharmaceuticals (Hawley, 1981; US EPA, 1988).
On the basis of the Gustafson (1989) groundwater ubiquity score, DNOC is considered to have a limited potential to leach from soil to groundwater.
DNOC is metabolized in soil. One bacterium of the Arthrobacter species is capable of using the compound as its source of carbon and nitrogen (Gasiewicz, 1991). It was also demonstrated that DNOC is rapidly inactivated in soil by a form of Corynebacterium simplex with formation of nitrite (Jensen & Gundersen, 1955). The biological decomposition of DNOC in soils was reviewed by Jensen (1966).
Tewfik & Evans (1966) have isolated a Pseudomonas species able to degrade DNOC in soils. The degradation of DNOC by 31 strains of Rhizobium and 5 strains of Azotobacter has been described (Hamdi & Tewfik, 1970); this microflora is important in nitrogen fixation.
The degradation of DNOC in three types of standard soils was investigated over a period of 88 days, at 20 °C, in the dark, at an application rate of 4.9 mg 14C-labelled DNOC/kg (dry weight) of soil. This is equivalent to a field application rate of 5 kg DNOC/ha. The DT50 was determined to be 1.7, 5.9 or 12 days, depending on the soil type. The main final degradation product of the aromatic ring was carbon dioxide, representing 39% of the applied radioactive dose; the main non-volatile metabolite was 2-methyl-4-nitrophenol, representing 40% of the applied radiocarbon between day 10 and day 20, and declining thereafter. The amount of bound residues in soil after extraction with organic solvents increased over the course of the study to reach 37% (Bieber, 1995). The presence of 2-methyl-4-nitrophenol as a decomposition product of DNOC in soil was confirmed by Verheij & van der Graaf (1995) by combined liquid chromatography–mass spectrometry (LC–MS) and tandem mass spectrometry (MS–MS).
DNOC has been identified in extracts of rain (Leuenberger et al., 1988; Alber et al., 1989), and snow (Alber et al., 1989). One pathway through which DNOC can enter the atmosphere is from overspray during use on agricultural products. DNOC has been detected in rain throughout the year, and its concentrations in rain did not show a trend with seasonal applications to crops (Leuenberger et al., 1988). These observations, and its low volatility, indicate that DNOC most likely enters the atmosphere through another mechanism. The low air–water partition coefficient of DNOC allows it to be scavenged effectively by precipitation, and enriched in humid aerosols, fog, clouds and rain droplets.
Biodegradation is the most significant process for removal from water and soil.
In the plastics industry, workers may be exposed to dusts when the damping water is removed before use. DNOC is used to inhibit immediate polymerization of styrene during the distillation and purification stages of manufacture. During the process, DNOC remains in the distillation columns, thereby ensuring that the finished styrene monomer contains no residues. The distillation process allows recycling of some DNOC, and the remaining DNOC-rich by-products are incinerated, thereby greatly reducing the risk of occupational and environmental exposures.
Table 4 summarizes the time-weighted average (TWA) values for occupational exposures.
In the former USSR, a maximum allowable concentration in the working zone (MACWZ) of 0.05 mg/m3 as a mixture of vapour and aerosol; a value of 0.002 mg/m3 for the lightest short, single exposure, tentatively safe exposure level in the atmosphere of residential areas (TSELhm); and a value of 0.05 mg/litre for surface water were established (Izmerov et al., 1982).
WHO (1982) indicates: "there exists a fair agreement, although no adequately valid relationship has yet been established, that – on the basis of human data – a blood DNOC level below 20 mg/litre will probably not lead to manifest health impairment"; the Dutch Expert Committee on Occupational Standards recommended a biological operator exposure limit (BOEL) in whole blood of 10 µg/ml. In their report, prepared on behalf of the Industrial Medicine and Hygiene Unit of the Health and Safety Directorate of the Commission of the European Communities, Jongerius & Jongeneelen (1991) recommended, based on human exposure data, a BOEL of 10 µg/ml in serum or 5 µg/ml in whole blood for workers not exposed to heat stress.
Table 4. TWA values for DNOC occupational exposures
| Country | TWA
(mg/m3 per 8 h) |
Year established |
| Argentina | 0.2 | 1991 |
| Canada | 0.2 | 1994 |
| Finland | 0.2 | 1996 |
| Denmark | 0.2 | 1996 |
| Germany | 0.2 | 1996 |
| Mexico | 0.2 | 1991 |
| Netherlands | 0.2 | 1996 |
| Norway | 0.2 | 1996 |
| UK | 0.2 | 1996 |
| USA (OSHA) | 0.2 | 1996 |
| USA (NIOSH) | 0.2 (10 h) | 1996 |
Source: UNEP Chemicals (IRPTC) (1999).
DNOC may be absorbed through the skin as well as by ingestion or inhalation of aerosols. The skin is the principal route of exposure in agricultural workers. The metabolic pathway of DNOC is identical in several non-ruminant mammalian species, but the rate at which it is cleared from the organism varies between species. In ruminants, DNOC undergoes an initial phase of bacterial metabolism in the rumen before it is absorbed into the blood.When applied under the same conditions as an oily formulation, the peak plasma concentrations represent 5.0% of the applied dose in males and 5.8% in females (38–45 µg/ml of blood). The peak plasma level occurred after 8 h in males and 24 h in females. The average t½ absorption was 2.8 h and the average t½ elimination was 34 h.
DNOC is more readily absorbed through the skin in oily formulation than when in aqueous solution; the peak plasma concentration is higher and is reached earlier. However, elimination remains fairly rapid, and the residual plasma and skin levels are comparable for the two types of formulation (Fabreguettes, 1993).
Following a single dose by gavage, the maximum plasma concentration is reached in 2–4 h in rats, and in 4–6 h in rabbits (Gasiewicz, 1991).
A single oral dose of 14C-labelled DNOC (0.4 mg/kg b.w.) given to two rats resulted in the following tissue distribution:
A field study of 18 sprayers showed that a daily exposure to DNOC leads to continuous elevation of DNOC level in the blood. The plasma levels increased daily and, at the end of the season, plasma levels ranged from 11 to 88 µg/ml (van Noort, 1960).
Leegwater et al. (1982) and van der Greef & Leegwater (1983) have identified similar metabolites as well as two other new ones, not previously described: 4,6-diacetamido-o-cresol (DAcAOC) and 4,6-dinitro-2-hydroxymethylphenol (DNHMP) in the urine of rats treated with a single oral dose of 0.4 or 6.0 mg DNOC/kg b.w., and in the urine of a rabbit administered orally a single dose of 20 mg DNOC/kg b.w.
Based on these observations, it may be concluded that rats and rabbits metabolize DNOC along the same pathway (Fig. 1) as suggested by Leegwater et al. (1982) with slight modification.
In an in vitro study in which DNOC was incubated with the contents of rat caecum, a rapid reduction to 6-ANOC occurred and 6-ANOC was then converted to DAOC. After 12 h of contact, 90% of the initial concentration of DNOC had been metabolized to DAOC (Ingebritsen & Froslie, 1980).
In ruminants (cattle), DNOC induces methaemoglobinaemia when administered intra-ruminally. This effect is related to the reduction process mediated by microflora that occurs in the rumen, leading to the formation of aminophenols and diaminophenols, which are known to be methaemoglobin-forming compounds (Harvey, 1958; Froslie & Karlog, 1970; Froslie 1973). The role of the microflora in the metabolism of DNOC by ruminants was confirmed experimentally in sheep by Jegatheeswaran & Harvey (1970).
In female rabbits, the half-life was determined to be approximately 6.5 h. After repeated dosing in humans, the DNOC level in blood increases more than that in laboratory animals (Harvey et al., 1951), because it is excreted at a slower rate in humans than in animals (Parker et al., 1951; Pollard & Filbee, 1951). In humans, the half-life of DNOC has been calculated from blood levels measured under circumstances related to heavy occupational exposure. The half-lives so determined varied from 96 h (van Noort, 1960) to 148 h (Jastroch et al., 1978) or 153.6 h (Pollard & Filbee, 1951) in severely poisoned sprayers. Lawford et al. (1954) have demonstrated that the elimination rate in descending order was:
Van den Berg et al. (1991) found that DNOC is an in vitro competitor for the thyroxine (T4) binding site on the plasma protein transthyretin. This plasma protein is a carrier for vitamin A and hormones, including T4. Speculations suggest that DNOC may alter thyroid hormone levels in plasma, thereby affecting thyroid functions.
Table 5. Acute toxicity of DNOC in laboratory animals
| Route | Species | LD50/LC50
(mg/kg b.w.)a |
Reference |
| Oral | rat | 20 (at 37–40 °C) | King & Harvey (1953a) |
| Oral | rat | 25 | Ben Dyke et al (1970) |
| Oral | rat | 30 (minimum lethal dose) | Ambrose (1942) |
| Oral | rat | 31 | Driscoll (1995 a) |
| Oral | rat | 50 | Spencer et al (1948) |
| Oral | rat | 85 | Burkatskaya (1965b) |
| Oral | cat | 50 | Jongerius & Jongeneelen (1991) |
| Oral | mouse | 16 | Jongerius & Jongeneelen (1991) |
| Oral | mouse | 47 | Jongerius & Jongeneelen (1991) |
| Oral | pig | 50–100 | McGirr & Papworth (1953) |
| Dermal | rat | 200–600 | Ben Dyke et al (1970) |
| Dermal | rat | >2000 | Driscoll (1995b) |
| Dermal | rabbit | 500 (no effect) | Burkatskaya (1965b) |
| Dermal | rabbit | 1000 | Burkatskaya (1965b) |
| Dermal | mouse | 187 | Arustamyn (1972) |
| Dermal | guinea-pig | 200 (no effect) | Jongerius & Jongeneelen (1991) |
| Dermal | guinea-pig | 500 (LD100) | Spencer et al (1948) |
| Inhalation | rat | 100 mg/m3 (4 h) (no effect) | King & Harvey (1953) |
| Inhalation | rat | 230 mg/m3 (4 h) | Dey-Hazra & Heisler (1981) |
| Inhalation | cat | 40 mg/m3 (4 h) | Burkatskaya (1965a) |
| Intraperitoneal | rat | 29. | Gasiewicz (1991) |
| Intraperitoneal | mouse | 24–26 | Gasiewicz (1991) |
| Intraperitoneal | rabbit | 24 | Jongerius & Jongeneelen (1991) |
| Intraperitoneal | guinea-pig | 23 | Jongerius & Jongeneelen (1991) |