PESTICIDE RESIDUES IN FOOD - 1997
Sponsored jointly by FAO and WHO
with the support of the International Programme
on Chemical Safety (IPCS)
TOXICOLOGICAL AND ENVIRONMENTAL
EVALUATIONS 1994
Joint meeting of the
FAO Panel of Experts on Pesticide Residues
in Food and the Environment
and the
WHO Core Assessment Group
Lyon 22 September - 1 October 1997
The summaries and evaluations contained in this book are, in most
cases, based on unpublished proprietary data submitted for the purpose
of the JMPR assessment. A registration authority should not grant a
registration on the basis of an evaluation unless it has first
received authorization for such use from the owner who submitted the
data for JMPR review or has received the data on which the summaries
are based, either from the owner of the data or from a second party
that has obtained permission from the owner of the data for this
purpose.
MEVINPHOS
First draft prepared by
Dr W. Erichson
Environmental Fate and Effects Division
US Environmental Protection Agency
Washington DC, USA
Identity and physical and chemical properties
Sources of environmental exposure
Environmental transport, distribution, and transformation
Effects on nontarget organisms in the laboratory and the
field
Evaluation of effects on the environment
Risk assessment
Terrestrial organisms
Aquatic environment
References
1. Identity and physical and chemical properties
Mevinphos is produced as a mixture of E (> 60%) and Z (< 25%)
geometrical isomers. It is a pale-yellow liquid with a boiling-point
of 99-103°C at 0.03 mm Hg (0.004 kPa) and a vapour pressure of 0.003
mm Hg (0.0004 kPa) at 21°C. Mevinphos is miscible in water, with an
estimated solubility of 600 000 mg/L. The octanol:water partition
coefficient (Kow) is 1.1-1.5.
2. Sources of environmental exposure
Mevinphos is a broad-spectrum organophosphate insecticide and
acaricide with both contact and systemic activity. Its mechanism of
pesticidal action is direct inhibition of cholinesterase. Mevinphos
was used to control aphids, mites, grasshoppers, cutworms,
leafhoppers, caterpillars, and other insects, predominantly on a
variety of vegetable, fruit, and field crops. All uses of mevinphos
were voluntarily withdrawn in the United States from 1 December 1995
owing to concerns about workers' health.
Mevinphos products have been formulated as emulsifiable concentrates,
soluble concentrates, ready-to-use liquids, and dusts. Its trade names
included Phosdrin, Duraphos, Apavinphos, OS-2046, Mevinox, Menite,
Gesfid, Phosfene, and Compound 2046. The application rates were
0.15-3.4 kg ai/ha but were typically 0.56-1.12 kg ai/ha per
application for most crops when distributed with conventional ground
or aerial equipment. Multiple applications were allowed as needed.
3. Environmental transport, distribution, and transformation
The available data on the environmental fate of mevinphos indicate
that it dissipates rapidly in the terrestrial environment. In one
field study in the San Joaquin Valley of California (USA), six
applications of 0.9 kg ai/ha were made from a tractor-mounted boom
sprayer at seven-day intervals, for a total application of 5.4 kg
ai/ha. The residues of the E and Z isomers in the top 15 cm of
soil on the day of application were reported to be < 0.01 mg/g soil;
the half-lives of the isomers in soil were difficult to determine
owing to the low concentrations of residues and the rapid degradation
of mevinphos, but they were less than four days for both isomers
(Leech & McKane, 1990).
Biotic degradation appears to be a main route of terrestrial
dissipation of mevinphos. The aerobic half-lives for the E and Z
isomers are 1.21 and 3.83 h, respectively, under laboratory conditions
at 25°C in the dark (Reynolds, 1994, 1995). The major degradation
pathways appear to be the formation of methylacetoacetate followed by
rapid binding to soil and mineralization to carbon dioxide. The
anaerobic half-life of mevinphos (a mixture of E and Z isomers) in
flooded sandy soil after 24 h of aerobic incubation is about 12 days.
Both the E and Z isomers hydrolyse faster in sterile aqueous
buffered solutions at pH 9 (2.8-7.5 days) than at pH 5 (50.8-84.6
days) or pH 7 (29.2-62.7 days) (Misra, 1992). At pH 5 and pH 7, both
isomers hydrolysed mainly to O-des-methylmevinphos. At pH 9, both
isomers produced O-des-methylmevinphos, acetoacetic acid, and
acetone, but the E-isomer also produced cis-mevinphos acid.
Photolysis of E-mevinphos in sterile, buffered (pH 5) aqueous
solution under artificial sunlight at 25°C occurred within 27.2 days
(Cohen, 1994a). After 480 h of exposure, the degradates included
Z-mevinphos, O-desmethylmevinphos, methyl acetoacetate, and an
unknown product. Aqueous photolysis of the Z isomer occurred within
27.8 days, with degradation to E-mevinphos, O-desmethyl-mevinphos,
and an unknown product (Cohen, 1994b).
Mevinphos is potentially highly mobile in soil, because of its high
solubility in water (6 × 105mg/L) and low soil partition coefficient
(Kads, 0.392-1.92). A study conducted in California (USA), however,
showed that leaching of the E and Z isomers in the field is
minimal. Residues of both isomers were detected below the soil surface
(0-15 cm) in only a few instances after application of mevinphos at
0.9 kg ai/ha weekly for seven weeks. It was concluded that rapid
degradation of both isomers in the top 15 cm of soil precluded
leaching to greater depths (Leech & McKane, 1990).
4. Effects on nontarget organisms in the laboratory and the field
The acute oral LD50 value of mevinphis in birds is 1.34-4.6 mg ai/kg
for sharp-tailed grouse, ring-necked pheasant, and mallard (Table 1).
When given in the diet, the LC50 was 236 mg ai/kg diet for Japanese
quail and 246 mg ai/kg diet for ring-necked pheasant; it was less
toxic to bobwhite quail and mallard ducks. The acute oral LD50 value
in laboratory rats was 2.2 mg ai/kg.
Table 1. Toxicity of mevinphos to birds
Species Age End-pointa Toxicity Reference
(mg ai/kg)
Sharp-tailed grouse Not specified LD50 501.34 Hudson et al. (1984)
(Tympanuchus phasianellus)
Ring-necked pheasant 3-4 months LD50 1.37 Hudson et al. (1984)
(Phasianus colchicus) 10 days LC50 246 Hill et al. (1975)
Mallard (Anas platyrhynchos) 5-7 months LD50 4.63 Hudson et al. (1984)
10 days LC50 1991 Hill et al. (1975)
Reproduction < 4 / 4 Beavers et al. (1992a)
(NOEC/LOEC)
Japanese quail 14 days LC50 236 Hill et al. (1975)
(Coturnix coturnix)
Bobwhite quail < 10 LC50 1000 DeWitt et al. (1963)
(Colinus virginianus) Reproduction 1.5/7.1 Beavers et al. (1992b)
(NOEC/LOEC)
a LD50 = single oral dose; LC50 = 5-day exposure to treated food followed by 3-day exposure to untreated food
The NOEC for reproductive toxicity was 1.5 mg ai/kg for bobwhite quail
and < 4 mg ai/kg for mallards exposed to mevinphos in the diet for
20-22 weeks. The number of viable embryos and the eggshell thickness
of bobwhite quail were significantly reduced at 7.1 mg ai/kg in
comparison with the control. The body weight of mallard hens was
significantly affected at 4 mg ai/kg.
The LD50 values for honeybees were 0.070 mg/bee after contact and
0.027 mg/bee after oral exposure (Stevenson, 1968). Mevinphos residues
were not toxic to bees 4 h after an application of 0.9 kg ai/ha
(Castellon, 1989). Mevinphos applied at standard field rates was toxic
to predaceous mites, parasitic wasps, and predaceous beetles in
several studies (Bartlett, 1963, 1964, 1966).
The toxicity of mevinphos to freshwater organisms is summarized in
Tables 2 and 3. The 96-h LC50 values for technical-grade mevinphos
(60% E isomer and 40% related compounds) in fish are 11.9 mg ai/L
for rainbow trout and 22.5-87 mg ai/L for bluegill sunfish. The values
for the formulated product (30.2-34.6% ai) are 81.4 mg ai/L for
bluegill sunfish, 41.8 mg ai/L for rainbow trout, and 1.46 mg ai/L for
Daphnia magna. The 48-h EC50 values for the technical-grade
material are 0.18 mg ai/L for Daphnia pulex and 0.42 mg ai/L for
Simocephalus serrulatus. The 96-h EC50 values for invertebrates
were 2.8-130 mg ai/L for Gammarus fasciatus at water temperatures of
15-21°C, 5 mg ai/L for Pteronarcys californica, 13.5 mg ai/L for
Palaemonetes kadiakensis, and 61 mg ai/L for Asellus brevicaudus.
The toxicity of mevinphos to estuarine and marine organisms is
summarized in Tables 2 and 3. The 96-h LC50 values for sheepshead
minnows are 0.81 mg ai/L for total mevinphos and 0.67 mg ai/L for its
E isomer, and those for mysid shrimp are 1.3 and 1.08 mg ai/L,
respectively. The 96-h EC50 value for shell deposition in eastern
oysters is > 1 mg ai/L.
Longer studies are not appropriate, given the rapid degradation of the
compound.
Deaths have been reported among wildlife exposed to mevinphos in
Scotland, but all of the incidents involved misuse (Hamilton et al.,
1981). The US Environmental Protection Agency (personal communication)
has received only one documented incident of acute poisoning of birds
with mevinphos. In that incident, 120 starlings and blackbirds were
found dead near treated cole crops in California. The cause of death
was confirmed to be mevinphos on the basis of a mean concentration of
1.3 mg/kg residues in the gizzard contents. Although mevinphos
dissipates rapidly and exposure may be brief, its high acute toxicity
clearly poses a danger to exposed wildlife.
Table 2. Toxicity of mevinphos to fish
Species Mean Test material Static/ End-point Toxicity Reference
size/age (% ai) Flow (mg ai/litre)
Freshwater species
Bluegill (Lepomis macrochirus) 0.9-1.3 g 60 Static 96-h LC50 22.5-87 Mayer & Ellersieck
(1986)
0.45 g 34.6 Flow 96-h LC50 81.4 Ward (1992a)
Rainbow trout 0.9 g 60 Static 96-h LC50 11.9 Mayer & Ellersieck
(1986)
(Oncorhynchus mykiss) 0.51 g 34.6 Flow 96-h LC50 41.8 Ward (1992b)
Largemouth bass 0.8 g 60 Static 96-h LC50 115 Mayer & Ellersieck
(Micropterus salmoides) (1986)
Estuarine and marine species
Sheepshead minnow Juvenile 100 Flow 48-h LC50 640 Mayer (1986)
(Cyprinodon variegatus) 0.33g 74.48 E-isomer, Flow 96-h LC50 670-810 Yurk (1991)
15.09 Z-isomer
Table 3. Toxicity of mevinphos to aquatic invertebrates
Species Mean Test material Static/ End-point Toxicity Reference
size/age (% ai) Flow (mg ai/litre)
Freshwater species
Water flea (Daphnia magna) < 24 h 30.2 E-isomer Flow 96-h EC50 1.5 Lintott (1992)
Water flea (Daphnia pulex) 1st instar 60 Static 48-h EC50 0.18 Mayer & Ellersieck
(1986)
Simocephalus serrulatus 1st instar 60 Static 48-h EC50 0.42-0.49 Mayer & Ellersieck
(1986)
Gammarus fasciatus Immature 60 Static 96-h EC50 2.8-130 Mayer & Ellersieck
(1986)
Pteronarcys californica 1st year 60 Static 96-h EC50 5 Mayer & Ellersieck
(1986)
Palaemonetes kadiakensis Immature 60 Static 96-h EC50 13.5 Mayer & Ellersieck
(1986)
Asellus brevicaudus Early instar 60 Static 96-h EC50 61 Mayer & Ellersieck
(1986)
Estuarine and marine specie
Mysid shrimp < 24 h 74.48 E-isomer, Flow 96-h LC50 1.03 Vaishnav et al.
(Mysidopsis bahia) 15.09 Z-isomer (1991)
Eastern oyster Juvenile 100 Flow EC50 (shell > 1000 Mayer (1986)
(Crassostrea virginica) deposition)
Brown shrimp (Penaeus aztecus) Juvenile 100 Flow 48-h EC50 150 Mayer (1986)
Residues resulting from application of 0.9 kg ai/ha were not toxic to
bees 4 h after application (Castellon, 1989), but mevinphos applied at
standard field rates was highly toxic to predaceous mites, parasitic
wasps, and predaceous beetles in several studies (Bartlett, 1963,
1964, 1966).
The US Environmental Protection Agency Office of Pesticides Program
uses the 'generic expected environmental concentration' to estimate
the aquatic PEC values for use in preliminary risk assessments. Acute
risk is assessed on the basis of peak PEC values from single and/or
multiple applications. Chronic risk is assessed from 21-day average
PECs for invertebrates and 56-day average PECs for fish; however, as
chronic toxicity is not applicable to mevinphos, the chronic risk to
aquatic organisms was not assessed.
In this calculation, the soil:water partition coefficient, the
degradation half-lives, and information given on the label are used to
estimate runoff from a 10-ha field into a 1-ha, 2-m deep pond. It
accounts for reductions in dissolved pesticide concentrations due to
adsorption to soil or sediment, soil incorporation, degradation in
soil before washoff into the pond, and degradation of the pesticide
within the pond. The model also accounts for direct deposition of
spray drift into the pond (1% of the application rate assumed for
ground application and 5% for aerial spray applications), the number
of applications, and the interval between applications. The model
assumes that runoff from a single, large rainstorm is sufficient to
remove 10% of the pesticide two days after the final application. The
environmental fate values used in the model are soil KOC = 1,
solubility = 6 × 105mg/L, aerobic soil metabolism half-life = 1 day,
hydrolytic half-life = 16 days, and water photolytic half-life = 27
days.
The PEC values for single aerial and ground sprays at application
rates of 1.12 kg ai/ha and 0.56 kg ai/ha are presented in Table 4. The
peak PEC is 16 mg ai/L for a single aerial application. The TER
values, ranging from < 0.01 to 0.08, indicate that mevinphos applied
Table 4. Predicted environmental concentrations (PECs) after
single aerial and ground spray applications of mevinphos
Application ratea Method of Peak PEC
(kg ai/ha) application (µg ai/litre)
1.12 Aerial spray 16
Ground spray 14
0.56 Aerial spray 8
Ground spray 7
a Based on the product label for Phosdrin 4 EC (US Environmental
Protection Agency registration no. 5481-412, accepted 16/5/94)
at a typical rate of 1.12 kg ai/ha presents 'very large' acute risks
to freshwater, estuarine, and marine invertebrates (Table 5). The
acute risk to freshwater fish is classified as 'large' on the basis of
the TER value of 0.74, but that to estuarine and marine fish is low
(TER = 50.6). Although no incidents of fish kills due to mevinphos
have been reported, overspray of fresh water should be avoided.
5. Evaluation of effects on the environment
Mevinphos is a broad-spectrum organophosphate insecticide and
acaricide with both contact and systemic activity. It is a mixture of
E (> 60%) and Z (< 25%) geometrical isomers. Its pesticidal
action is due to direct inhibition of cholinesterase activity. It is
used (except in the United States) to control aphids, mites,
grasshoppers, cutworms, leafhoppers, caterpillars, and other insects
on a variety of vegetable, fruit, and field crops. The available
formulations include emulsifiable concentrates, soluble concentrates,
ready-to-use liquids, and dusts.
Mevinphos dissipates rapidly in the terrestrial environment. The
half-lives of both isomers in soil are less than four days. Biotic
degradation is the major means of terrestrial dissipation. The main
degradation pathway appears to be the formation of methylacetoacetate,
followed by rapid binding to soil, and mineralization to carbon
dioxide. Under laboratory conditions at 25°C in the dark, the aerobic
half-lives of the E and Z isomers are 1.21 and 3.83 h,
respectively. The half-lives for hydrolysis of the isomers in sterile
aqueous buffered solution are related to the pH: pH 9, 2.8-7.5 days;
pH 5, 50.8-84.6 days. O-Desmethylmevinphos is the major product.
The photolysis half-life in aqueous solution was about 27 days for
both isomersœ Mevinphos is potentially very mobile in soils because of
its high solubility in water (6 × 105 mg/L) and low soil partition
coefficients (Kads, 0.392-1.92), but rapid degradation of both isomers
in the top 15 cm of soil prevents further leaching.
Mevinphos is toxic to birds, with acute oral LD50 values ranging from
1.34-4.6 mg ai/kg bw for sharp-tailed grouse, ring-necked pheasants,
and mallards The dietary LC50 values were 236 mg/kg diet for Japanese
quail and 246 mg/kg diet for ring-necked pheasants. In bobwhite quail
and mallards exposed to mevinphos in the diet for 20-22 weeks, the
NOEC values for reproductive toxicity were 1.5 ppm ai and < 4 ppm ai,
respectivelyœ The number of viable embryos and the eggshell thickness
of bobwhite quail were significantly reduced at 7.1 ppm ai and the
body weights of mallard hens were significantly affected at 4 ppm ai.
The oral LD50 value for laboratory rats was 2.2 mg ai/kg bw.
Mevinphos is toxic to a number of insect species. In the laboratory,
the LD50 values for honeybees were 0.070 µg/bee for contact and 0.027
µg/bee for oral exposure. Mevinphos applied at standard field rates
was toxic to predaceous mites, parasitic wasps, and predaceous
beetles.
Table 5. Risks to aquatic organisms after single exposures
Risk category Toxicity value PECa Toxicity:exposure Risk
(µg ai/litre) (µg ai/litre) ratio (TER) classification
Freshwater fish 11.9 16 0.74 Large
Freshwater invertebrates 0.18 16 0.01 Very large
Estuarine and marine fish 810 16 50.6 Low
Estuarine and marine invertebrates 1.3 16 0.08 Very large
a Calculated from the 'generic expected environmental concentration' model of the US Environmental
Protection Agency; acute exposure is based on peak PEC values for a single aerial application of
1.12 kg ai/ha
b Value for toxicity divided by the PEC
Mevinphos is toxic to fish. The 96-h LC50 values for technical-grade
mevinphos (60% E isomer and 40% related compounds) were 11.9 µg ai/L
for rainbow trout and 22.5-87 µg ai/L for bluegill sunfish. The 96-h
LC50 values for the formulated product (30.2-34.6% ai) were 81.4 µg
ai/L for bluegill sunfish, 41.8 µg ai/L for rainbow trout, and 1.46 µg
ai/L for Daphnia magna. The 48-h LC50 values for the technical-
grade material were 0.18 µg ai/L for Daphnia pulex and 0.42 µg ai/L
for Simocephalus serrulatus. The 96-h LC50 values for other
invertebrates include 2.8-130 µg ai/L for Gammarus fasciatus in
water temperatures of 15-21°C, 5 µg ai/L for Pteronarcys
californica, 13.5 µg ai/L, for Palaemonetes kadiakensis, and 61 µg
ai/L for Asellus brevicaudus.
For estuarine and marine organisms, the 96-h LC50 values were 0.81 mg
ai/L for total mevinphos and 0.67 mg ai/L for its E isomer in
sheepshead minnows, and 1.3 and 1.08 µg ai/L in mysid shrimp,
respectively. The 96-h EC50 for shell deposition in eastern oysters
was > 1 mg ai/L. Longer studies are not appropriate in view of the
rapid degradation of the compound.
Risk assessment
(a) Terrestrial organisms
Terrestrial organisms may be exposed to mevinphos by consuming
contaminated foods and/or by dermal contact with contaminated soil and
vegetation. The risk posed by foliar sprays is assessed by comparing
the dietary LC50 values with the predicted environmental
concentrations (PECs) of mevinphos on potential avian food items
(grass, insects, and seeds). The PEC values are based on the Kenaga
nomogram (Hoerger & Kenaga, 1992) as modified by Fletcher et al.
(1994). The maximum PECs immediately after a single, direct
application of mevinphos at 1.12 kg ai/ha are 240 mg ai/kg for short
grasses, 135 mg ai/kg for small insects, and 15 mg ai/kg for seeds.
For birds, the toxicity:exposure ratios (TERs), based on comparisons
of the PECs with the lowest LC50 value seen in dietary tests for
acute risk, are given in Table 6.
This analysis indicates that mevinphos applied at a typical rate of
1.12 kg ai/ha presents 'very large' to 'present' acute risks to
herbivorous (TER = 1.0) and insectivorous (TER = 1.7) birds, wheres
that to granivores is expected to be 'low' (TER = 15.7)œ Deaths due to
exposure to mevinphos have been reported, but most of the incidents
involved misuse. Although mevinphos dissipates rapidly and exposure
may be brief, its high acute toxicity clearly poses a danger to
exposed wildlifeœ
Table 6. Toxicity:exposure ratios (TERs) for birds
Toxicitya PECb TERc Risk classification
LC50 = 236 240 (short grass) 1.0 Very large
(Japanese quail) 135 (small insects) 1.7 Present
15 (seeds) 15.7 Low
a For the most sensitive species tested
b Maximum PECs after a single application of 1.12 kg ai/ha
c Value for toxicity divided by value for exposure (i.e. PEC)
The hazard ratios for honeybees exposed after application at a rate of
1120g ai/ha, based on the LD50 values, were 16 000 for contact and 37
333 for oral exposure, indicating a high risk. Mevinphos should not be
applied or allowed to drift onto blooming crops or weeds while bees
are visiting the treated area. Mevinphos applied at standard field
rates was highly toxic to predaceous mites, parasitic wasps, and
predaceous beetles in several studies.
(b) Aquatic organisms
Aquatic organisms may be exposed to mevinphos from surface water
runoff and soil erosion and/or drift from treated sites into water
bodies.
The risk posed by mevinphos is assessed on the basis of the 'generic
expected environmental concentration'. Acute risk is assessed from
peak PECs after single and/or multiple applications. Because chronic
toxicity is not relevant for mevinphos, the chronic risk to aquatic
organisms was not assessed.
The environmental fate values used in the assessment of mevinphos are
soil KOC = 1, solubility = 6 × 105 mg/L, aerobic soil degradation
half-life = 1 day, hydrolytic half-life = 16 days, and water
photolytic half-life = 27 days. The PEC values after single aerial and
ground spray applications of mevinphos at rates of 1.12 and 0.56 kg
ai/ha are shown in Table 4.
The TERs for mevinphos in aquatic invertebrates are 0.01-0.08 (Table
5), indicating that mevinphos applied at a typical field application
rate of 1.12 kg ai/ha presents 'very large' acute risks to freshwater,
estuarine, and marine invertebrates. The acute risk to freshwater fish
is classified as 'large' on the basis of the TER of 0.74, but that to
estuarine and marine fish is low (TER = 50.6). Although no incidents
of fish kills due to mevinphos have been reported, overspray of
freshwaters should be avoided.
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