Dichlorvos
(endorsed 2011)
Guideline
Based on human health concerns, dichlorvos in drinking water should not exceed 0.005 mg/L.
Related chemicals
Dichlorvos (CAS 62-73-7) belongs to the organophosphate class of chemicals. There are many other pesticides in this class, including acephate, chlorpyrifos, diazinon, fenitrothion, profenofos and trichlorfon (Tomlin 2006).
Human risk statement
With good water quality management practices, the exposure of the general population is expected to be well below levels that may cause health concerns.
If present in drinking water as a result of a spillage or through misuse, dichlorvos would not be a health concern unless the concentration exceeded 0.005 mg/L. Excursions above this level even for a short period are of concern, as the health-based guideline is based on short-term effects.
With good water quality management practices, pesticides should not be detected in source waters used for drinking water supplies. Persistent detection of pesticides may indicate inappropriate use or accidental spillage, and investigation is required in line with established procedures in the risk management plan for the particular water source.
General description
Uses: Dichlorvos is an insecticide and acaricide for the control of insects in a wide range of situations, including in domestic and public health situations, as well as in warehouses and storerooms and in animal houses. Dichlorvos is also used to control pests in a wide range of crops and is used as a veterinary anthelmintic.
There are registered products containing dichlorvos in Australia. These products are intended for professional and home garden use. The products used as insecticides are generally available as emulsifiable concentrates to be diluted and applied by spray. The veterinary products containing dichlorvos are formulated as an oral paste for veterinary use. Data on currently registered products are available from the Australian Pesticides and Veterinary Medicines Authority.
Exposure sources: The main sources of public exposure to dichlorvos are the use of home garden products and residues in food. Residue levels in food produced according to good agricultural practice are generally low.
Agricultural use of dichlorvos may potentially lead to contamination of source waters through processes such as run-off, spray drift or entry into groundwater.
The veterinary use of dichlorvos provides some potential for contamination of drinking water through the washing of equipment near dams, streams or watercourses.
Typical values in Australian drinking water
Dichlorvos has been routinely monitored by some water utilities in Australia. No detections above analytical limits of detection have been reported in the reviewed reports.
Treatment of drinking water
Coagulation achieves only 10-20% removal of organophosphorus pesticides. Ozone treatment can achieve complete degradation of dichlorvos under experimental conditions (Liu et al. 2009). Kim et al. (2002) reported a complete reduction of dichlorvos (initial concentration of 220 mg/L) by batch treatment with ozone at 1 mg/L. Good photocatalytic degradation/oxidation of dichlorvos has been reported using ultraviolet (UV) irradiation (Lu 1994, Liu et al. 2009) and UV/titanium dioxide (Evgenidou et al. 2005, Senthilnathan et al. 2009). A challenger advanced oxidation process test using ozone and hydrogen peroxide was able to reduce by 49% the influent concentration of dichlorvos, and the combination of advance oxidation and activated carbon filter reduced dichlorvos by 99% (USEPA 2007).
Nanofiltration using different membranes gave 4–87% removal from a 1 mg/L solution; adsorption onto the membrane was an important contributor to removal (Ozaki et al. 2000). A concentration of 0.01 μg/L was reduced by 98–99% by different ultra-low reverse osmosis membranes (Hofman et al. 1998). Reverse osmosis challenger test with an initial concentration of 1300 μg/L was efficient in removing dichlorvos (95% removal) (USEPA 2005).
Measurement
Dichlorvos is included in the United States Environmental Protection Agency (USEPA) gas chromatographic Method 622. The extract is concentrated and analyzed by gas chromatography using a flame photometric or phosphorus/nitrogen detector (Pressley et al. 2002). Hollow fibre-liquid phase microextraction with gas chromatography by flame thermionic detection can achieve a limit of detection of 32 ng/L for dichorvos (Lambropoulou et al. 2005). Enzyme-linked immunosorbent assay (IC-ELISA) method can achieve a limit of quantitation of 0.048 μ/mL for dichlorvos (Tang et al. 2008).
History of the health values
The current acceptable daily intake (ADI) for dichlorvos is 0.001 mg per kg of bodyweight (mg/kg bw), based on a no-observed-effect level (NOEL) of 0.014 mg/kg bw/day from a short-term (28-day) human study. The NOEL is based on plasma cholinesterase inhibition. The ADI incorporates a safety factor of 10, and was established in 2004.
The previous ADI was 0.0005 mg/kg bw based on a NOEL of 0.05 mg/kg bw/day for cholinesterase inhibition in a dog study, and using a safety factor of 100.
The acute reference dose (ARfD) of 0.1 mg/kg bw for dichlorvos was established in 2004, based on a NOEL of 1 mg/kg bw/day from a single oral dose study in human males. The ARfD incorporates a safety factor of 10.
The previous health value was 0.001 mg/L (NHMRC and NRMMC 2004).
Health considerations
Metabolism: Dichlorvos is readily absorbed from the gastrointestinal tract. It is extensively metabolised and rapidly excreted in the urine and as exhaled within 24 hours.
Acute effects: Dichlorvos has moderate to high acute oral and dermal toxicity in rats. It is a skin sensitiser in both humans and guinea pigs.
Short-term effects: In a 28-day dietary study in humans, there was inhibition of plasma cholinesterase activity at 0.021 mg/kg bw/day. The NOEL of 0.014 mg/kg bw/day in humans is the basis for the current ADI.
Inhibition of plasma and red blood cell cholinesterase activity was reported at 0.9 mg/kg bw/day and above in a 90-day dietary study in dogs, and at 1.5 mg/kg bw/day in a 13-week oral study in rats.
Long-term effects: In a 2-year rat study, inhibition of plasma and red blood cell cholinesterase activity was reported from 2.3 mg/kg bw/day. In a 2-year dog study, inhibition of red blood cell cholinesterase activity in males was reported at 0.08 mg/kg bw/day and above.
Carcinogenicity: The weight of evidence from long-term studies in rodents indicates that dichlorvos is not carcinogenic.
Genotoxicity: Dichlorvos was positive in some in vitro short-term assays, but not genotoxic in vivo.
Reproductive and developmental effects: A 2-generation reproduction study in rats reported effects on reproductive parameters at high dose levels, which were well in excess of the likely human exposure levels. Developmental studies in mice, rats and rabbits did not produce any evidence of effects on foetal development.
Neurotoxicity: Short-term oral studies in chickens and rats did not report any evidence of delayed neurotoxicity.
Poisons Schedule: Dichlorvos is included in Schedules 5, 6 and 7 of the Standard for the Uniform Scheduling of Medicines and Poisons No.1, 2010 (the Poisons Standard)(DoHA 2010), depending on its concentration and use. Current versions of the Poisons Standard should be consulted for further information.
Derivation of the health-based guideline
The health-based guideline of 0.005 mg/L for dichlorvos was determined as follows:
where:
0.014 mg/kg bw/day is the NOEL based on a short-term (28-day) study in humans.
70 kg is taken as the average weight of an adult.
0.1 is a proportionality factor based on the assumption that 10% of the ADI will arise from the consumption of drinking water.
2 L/day is the estimated maximum amount of water consumed by an adult.
10 is the safety factor applied to the NOEL derived from human studies to allow for intraspecies variation.
References
NOTE: The toxicological information used in developing this fact sheet is from reports and data held by the Department of Health, Office of Chemical Safety.
DoHA (2010) The Poisons Standard; Schedule 1-Standard for the Uniform Scheduling of Medicines and Poisons, Department of Health and Ageing, Commonwealth of Australia, Canberra.
Evgenidou E, Fytianos F, Poulios I (2005). Semiconductor-sensitized photodegradation of dichlorvos in water using and ZnO as catalysts. Applied Catalysis B: Environmental, 59(1/2):81-89.
Hofman JAMH, Beerendonk EF, Folmer HC, Kruithof JC (1998). Removal of pesticides and other micropollutants with cellulose-acetate, polyamide and ultra-low pressure reverse osmosis membranes. Desalination, 113(2-3):209-214.
Kim B, Fujita H, Sakai Y, Sakoda A, Suzuki M (2002). Catalytic ozonation of an organophosphorus pesticide using microporous silicate and its effect on total toxicity reduction. Water Science and Technology, 46(4/5):35-41.
Lambropoulou DA, Albanis TA (2005). Application of hollow fiber liquid phase microextraction for the determination of insecticides in water. Journal of Chromatography A, 1072(1):55-61.
Liu C, Qiang ZM, Tian F, Zhang T (2009). [Reactivity of several classes of pesticides with UV, ozone and permanganate]. Huan Jing Ke Xue, 30(1):127-33.
Lu M. C (1994). Photocatalytic oxidation of dichlorvos in the presence of hydrogen peroxide and ferrous iron. Water Science and Technology, 30(9):29-38.
NHMRC (National Health and Medical Research Council), NRMMC (Natural Resources Management Ministerial Council) (2004). Australian Drinking Water Guidelines. National Water Quality Management Strategy, Paper 6. NHMRC and NRMMC.
Ozaki H, Li H (2000). Rejection properties of non-phenylic pesticides with nanofiltration membranes. Journal of Membrane Science, 171(2):229-237.
Pressley T, Longbottom J (2002). Method 622 Method 622. The Determination of Organophosphorus Pesticides in Municipal and Industrial Wastewater.
Senthilnathan J, Philip L (2009). Removal of mixed pesticides from drinking water system by photodegradation using suspended and immobilized . Journal of Environmental Science and Health, Part B, 44(3):262-70.
Tang J, Zhang M, Cheng G, Li A, Lu Y (2008). Development of IC-ELISA for detection of organophosphorus pesticides in water. Journal of Environmental Science and Health, Part B, 43(8):707-12.
Tomlin CD (ed) (2006). The Pesticide Manual: a world compendium, 14th edition, British Crop Production Council, UK.
USEPA Method 622: The Determination of Organophosphorus Pesticides in Municipal and Industrial Wastewater, #600/4-82-008, NTIS #82-156027. Washington, DC, United States Environmental Protection Agency.
USEPA (United States Environmental Protection Agency) (2005). Point of use drinking water treatment system application: Removal of chemical contaminants in drinking water: Reverse osmosis. The Environmental Technology Verification Program, USEPA.
USEPA (United States Environmental Protection Agency) (2007). Point of use drinking water treatment system application: Removal of chemical contaminants in drinking water: Advanced simultaneous oxidation process. The Environmental Technology Verification Program, USEPA.
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