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Chlorpyrifos
February 1986
(edited March 1989)
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(PDF Version - 24 K)Table of Contents
- Guideline
- Identity, Use and Sources in the Environment
- Exposure
- Analytical Methods and Treatment Technology
- Health Effects
- Rationale
- References
Guideline
The maximum acceptable concentration (MAC) for chlorpyrifos in drinking water is 0.09 mg/L (90 µg/L).
Identity, Use and Sources in the Environment
Chlorpyrifos (C9H11Cl3NO3PS) is an organophosphorus insecticide used for the control of mosquitoes, flies, various crop pests in soil and on foliage, household pests and aquatic larvae. It is also used on sheep and cattle for the control of ectoparasites. Annual use in Canada is in the range of 100 000 to 500 000 kg.Footnote 1
The vapour pressure of chlorpyrifos is 2.49 x 10-3 Pa at 25°C, and its solubility in water is 2 mg/L at 25°C.Footnote 2 Reported log octanol-water partition coefficients are high, ranging from 4.82 to 5.11.Footnote 3
Chlorpyrifos is tightly absorbed by soil and is not expected to leach significantly.Footnote 4 It persists in soil for 60 to 120 days,Footnote 5 with degradation being primarily due to microbial action.Footnote 6 Products of degradation include 3,5,6-trichloro-2-pyridinol, which is subsequently broken down to organochlorine compounds and carbon dioxide.Footnote 7 The rate of hydrolysis of chlorpyrifos in water increases with pH and temperature and is enhanced by the presence of copper.5 Between 30 and 60% of the total amount of chlorpyrifos in the aqueous phase may disappear within 24 hours through adsorption, degradation and vaporization.Footnote 8
Exposure
Chlorpyrifos was not detected in a survey of 511 samples from municipal and private drinking water supplies encompassing Metropolitan Toronto (1971 to 1982), Manitoba (1986) and Alberta (1978 to 1985) (detection limits 0.20 and 0.04 µg/L).Footnote 9 It was not found in 446 samples taken from surface waters of the Grand River and Thames River basins, although nearly 3000 and 7500 kg/year, respectively, had been used in these areas (detection limit 0.1 µg/L).Footnote 10
Based on the residue tolerance limits set by the Food Directorate of the Department of National Health and Welfare,Footnote 11 the theoretical maximum daily intake of chlorpyrifos from food is 0.07 mg/d, which represents 10% of the acceptable daily intake (ADI) of 0.7 mg/d for a 70-kg adult.Footnote 12 Chlorpyrifos was detected in only 49 of 6391 domestic food samples in the United States, 94% of which had concentrations below 2.0 ppm; in imported foods, chlorpyrifos was detected in 1777 of 12 044 samples, with all but five samples containing concentrations at or below 0.5 µg/g.Footnote 13 The average daily dietary intake of chlorpyrifos has been estimated to be 0.241 µg, based on the U.S. market basket survey.Footnote 14
Analytical Methods and Treatment Technology
Organophosphorus insecticides in water may be analysed by extraction separately into hexane and dichloromethane, separation by gas chromatography and flame thermionic or flame photometric detection (detection limit 1 µg/L);Footnote 15 separation may also be accomplished by gas/liquid chromatography, followed by flame photometric detection (detection limit 0.1 µg/L).Footnote 16
No information was found on the effectiveness of current treatment technologies in removing chlorpyrifos from drinking water.
Health Effects
Chlorpyrifos is readily absorbed from the gastrointestinal tract and is rapidly metabolized. Metabolites are excreted principally in the urine and to a lesser extent in the faeces; the main metabolites are 3,5,6-trichloro-2-pyridylphosphate and 3,5,6-trichloro-2-pyridinol.Footnote 17 Small amounts of unmetabolized chlorpyrifos have been detected in the blood, brain and liver after accidental human ingestion.Footnote 18
Chlorpyrifos is a cholinesterase inhibitor. Human volunteers (four men per group) were administered oral doses of chlorpyrifos of 0.014 mg/kg bw per day for 27 days, 0.03 mg/kg bw per day for 20 days or 0.10 mg/kg bw per day for nine days.Footnote 19 Red blood cell cholinesterase activity was not affected at any level.
Beagle dogs were fed diets containing chlorpyrifos at dose levels of 0, 0.01, 0.03, 0.1, 1.0 or 3.0 mg/kg bw per day for two years.Footnote 20 Red blood cell cholinesterase was inhibited in males and females at 1.0 and 3.0 mg/kg bw per day. In a similar study,Footnote 21 rats were fed diets containing chlorpyrifos at concentrations of 0, 0.01, 0.03, 0.1, 1.0 and 3.0 mg/kg bw per day for two years. Brain cholinesterase activity was inhibited at 3.0 mg/kg bw per day and slightly depressed at 1.0 mg/kg bw per day. Based on these results, the no-observed-adverse-effect level (NOAEL) for red blood cell and brain cholinesterase inhibition is considered to be 0.1 mg/kg bw per day. The NOAEL in Rhesus monkeys receiving 0.08 mg/kg bw per day of chlorpyrifos by gavage for six months was similar; animals exhibited no depression in red blood cell cholinesterase activity.Footnote 22
In a carcinogenicity study in CD-1 mice, chlorpyrifos was not oncogenic when administered at dose levels up to 15 ppm (1.5 mg/kg bw per day) in food for 105 weeks.Footnote 23 Chlorpyrifos was not found to be mutagenic in five microbial assay systems.Footnote 24 In a CF-1 mouse teratogenicity study, chlorpyrifos was not teratogenic at doses up to 25 mg/kg bw per day, although significant reductions in plasma and erythrocyte cholinesterase levels were observed in maternal mice at 1 mg/kg bw per day or greater and in foetuses at 10 mg/kg bw per day or more.Footnote 25
Rationale
The ADI for chlorpyrifos has been derived by the Food and Agriculture Organization (FAO) and the World Health Organization (WHO)Footnote 12 as follows:
ADI = 0.1 mg/kg bw per day / 10 = 0.01 mg/kg bw per day
where:
- 0.1 mg/kg bw per day is the NOAEL derived from two-year studies in the dog and ratFootnote 20,Footnote 21 and studies with human volunteersFootnote 19
- 10 is the uncertainty factor.
The maximum acceptable concentration (MAC) for chlorpyrifos in drinking water is derived from the ADI as follows:
MAC = 0.01 mg/kg bw per day × 70 kg × 0.20 / 1.5 L/d ≈ 0.09 mg/L
where:
- 0.01 mg/kg bw per day is the ADI established by the FAO/WHO
- 70 kg is the average body weight of an adult
- 0.20 is the proportion of daily intake of chlorpyrifos allocated to drinking water
- 1.5 L/d is the average daily consumption of drinking water for an adult.
References
Footnotes
- Footnote 1
-
Environment Canada/Agriculture Canada. Pesticide Registrant Survey, 1986 report. Commercial Chemicals Branch, Conservation and Protection, Environment Canada, Ottawa (1987).
- Footnote 2
-
Agriculture Canada. Guide to the chemicals used in crop protection. 7th edition. Publication No. 1093 (1982).
- Footnote 3
-
Suntio, L.R., Shiu, W.Y., Mackay, D., Seiber, J.N. and Glotfelty, D. Critical review of Henry's Law constants for pesticides. Rev. Environ. Contam. Toxicol., 103: 1 (1988).
- Footnote 4
-
Hazardous Substances Databank. Toxicology Data Network. U.S. National Library of Medicine, Bethesda, MD (1988).
- Footnote 5
-
Worthing, C.R. The pesticide manual - a world compendium. 7th edition. British Crop Protection Council (1983).
- Footnote 6
-
Environment Canada. Canadian water quality guidelines. Prepared by the Canadian Council of Resource and Environment Ministers (1987).
- Footnote 7
-
The Royal Society of Chemistry. The agrochemicals handbook. 2nd edition (update 1 -- April 1988). Nottingham (1988).
- Footnote 8
-
Hughes, D.N., Boyer, M.G., Papst, M.H., Fowle, C.D., Rees, G.A.V. and Baulu, P. Persistence of three organophosphorus insecticides in artificial ponds and some biological implications. Arch. Environ. Contam. Toxicol., 9: 269 (1980).
- Footnote 9
-
Hiebsch, S.C. The occurrence of thirty-five pesticides in Canadian drinking water and surface water. Unpublished report prepared for the Environmental Health Directorate, Department of National Health and Welfare, January (1988).
- Footnote 10
-
Frank, R. and Logan, L. Pesticide and industrial chemical residues at the mouth of the Grand, Saugeen and Thames rivers, Ontario, Canada, 1981-85. Arch. Environ. Contam. Toxicol., 17: 741 (1988).
- Footnote 11
-
Department of National Health and Welfare. National pesticide residue limits in foods. Food Directorate, Ottawa (1986).
- Footnote 12
-
FAO/WHO. Pesticide residues in food -- 1982. Evaluations. Data and recommendations of the Joint Meeting on Pesticide Residues, Rome, 23 November - 2 December 1982. FAO Plant Production and Protection Paper No. 49, Food and Agriculture Organization of the United Nations, Rome (1983).
- Footnote 13
-
Hundley, H.K., Cairns, T., Luke, M.A. and Masumoto, H.T. Pesticide residue findings by the Luke method in domestic and imported foods and animal feeds for fiscal years 1982-1986. Assoc. Off. Anal. Chem., 71(5): 875 (1988).
- Footnote 14
-
Gartrell, M.J., Craun, J.C., Podebarac, D.S. and Gunderson, E.L. Pesticides, selected elements, and other chemicals in adult total diet samples, October 1980 - March 1982. J. Assoc. Off. Anal. Chem., 69(1): 146 (1986).
- Footnote 15
-
U.K. Department of the Environment. Methods for the examination of waters and associated materials -- organophosphorus pesticides in river and drinking water, 1980, tentative method. Her Majesty's Stationery Office, London (1983).
- Footnote 16
-
Braun, H.E. and Frank, R. Organochlorine and organophosphorus insecticides: their use in eleven agricultural watersheds and their loss to stream waters in southern Ontario, Canada, 1975-1977. Sci. Total Environ., 15: 169 (1980).
- Footnote 17
-
FAO/WHO. Data sheet on pesticides, No. 18 -- Chlorpyrifos. World Health Organization, Geneva (1975).
- Footnote 18
-
Lores, E.M., Bradway, D.E. and Moseman, R.F. Organophosphorus pesticide poisonings in humans: determination of residues and metabolites in tissues and urine. Arch. Environ. Health, 33. 270 (1978).
- Footnote 19
-
Coulston, F., Goldberg, L. and Griffin, T. Safety evaluation of Dowco 179 in humans. Unpublished report, Inst. Exp. Pathol. Toxicol., Albany Medical College (1972). (Reviewed in FAO/WHO. 1972 evaluations of some pesticide residues in food. WHO Pesticide Residue Series No. 2, World Health Organization, Geneva [1973].)
- Footnote 20
-
McCollister, S.B., Kociba, R.J., Gehring, P.J. and Humiston, C.G. Results of two-year dietary feeding studies on Dowco 179 in beagle dogs. Unpublished report T35.12-44793-18, Dow Chemical Co. (1971). (Reviewed in FAO/WHO. 1972 evaluations of some pesticide residues in food. WHO Pesticide Residue Series No. 2, World Health Organization, Geneva [1973].)
- Footnote 21
-
McCollister, S.B., Kociba, R.J., Gehring, P.J. and Humiston, C.G. Results of two-year dietary feeding studies of Dowco 179 in rats. Unpublished report NBT35.12-44793-21, Dow Chemical Co. (1971). (Reviewed in FAO/WHO. 1972 evaluations of some pesticide residues in food. WHO Pesticide Residue Series No. 2, World Health Organization, Geneva [1973].)
- Footnote 22
-
Coulston, F., Goldberg, L., Abraham, R., Benito, K.F., Griffin, T.B. and Norvell, M. Final report on safety evaluation and metabolic studies on Dowco 179 (IN 151). Unpublished report, Inst. Exp. Pathol. Toxicol., Albany Medical College (1971). (Reviewed in FAO/WHO. 1972 evaluations of some pesticide residues in food. WHO Pesticide Residue Series No. 2, World Health Organization, Geneva [1973].)
- Footnote 23
-
Warner, S.D., Gerbig, C.G., Strebing, R.J. and Molello, J.A. Results of a two-year toxicity and oncogenicity study of chlorpyrifos administered to CD-1 mice in the diet. Unpublished report, Dow Chemical Co. (1980), reviewed in reference 12.
- Footnote 24
-
Poole, D.C., Simmon, V.F. and Newell, G.W. In vitro mutagenic activity of fourteen pesticides. Toxicol. Appl. Pharmacol., 41: 196 (1977).
- Footnote 25
-
Deacon, M.M., Murray, J.S., Pilney, M.K., Dittenber, D.A., Hanley, T.R., Jr. and John, J.A. The effects of orally administered chlorpyrifos on embryonal and foetal development in mice. Unpublished report, Dow Chemical Co. (1979).
