Chlorothalonil
(endorsed 2011)
Guideline
Based on human health concerns, chlorothalonil in drinking water should not exceed 0.05 mg/L.
Related chemicals
Chlorothalonil (CAS 1897-45-6) belongs to the chloronitrile class of chemicals. There are no other pesticides in this class (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, chlorothalonil would not be a health concern unless the concentration exceeded 0.05 mg/L. Minor excursions above this level would need to occur over a significant period to be a health concern, as the health-based guideline is based on long-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: Chlorothalonil is a fungicide used for the control of fungal diseases in fruits and vegetables, as well as in turf, ornamentals, freshly sawn Pinus spp. timber, and in various tress and vine crops.
There are registered products that contain chlorothalonil in Australia. These products are intended for professional and for home garden use and are available as concentrated solutions to be applied in diluted form using ground or hand-held sprays. Data on currently registered products are available from the Australian Pesticides and Veterinary Medicines Authority.
Exposure sources: The main sources of public exposure to chlorothalonil and its metabolites 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 chlorothalonil may potentially lead to contamination of source waters through processes such as run-off, spray drift or entry into groundwater.
Typical values in Australian drinking water
No reports of chlorothalonil in Australian drinking waters have been identified. However, chlorothalonil has been occasionally identified in drinking source waters in the USA (Walker et al. 2000).
Treatment of drinking water
No specific data on the treatment of chlorothalonil in drinking water have been identified.
Measurement
Chlorothalonil can be measured in surface waters by liquid chromatography with ultraviolet (UV) detection, with a practical limit of quantitation of 25 ng/L (Ozhan and Alpertunga 2007). Similar detection limits may alternatively be achieved by solid-phase microextraction and gas chromatography coupled with electron-capture and mass spectrometric detection (Lambropoulou et al. 2000).
Chlorothalonil can be measured in surface waters by liquid chromatography with UV analysis
History of the health values
The current acceptable daily intake (ADI) for chlorothalonil is 0.01 mg per kg of bodyweight (mg/kg bw), based on a no-observed-effect level (NOEL) of 1.5 mg/kg bw/day from a long-term (2-year) dietary study in mice and dogs. The NOEL is based on lesions in the kidney and the stomach. The ADI incorporates a safety factor of 100 and was established in 1991.
The previous ADI was 0.4 mg/kg bw/day based on a NOEL of 800 mg/kg bw/day. The ADI incorporated a safety factor of 2000 and was set in 1973. In 1986, the Joint FAO/WHO Meeting on Pesticide Residues, recommended a temporary ADI of 0.0005 mg/kg bw based on a NOEL of 0.5 mg/kg bw and a safety factor of 1000. The NOEL was based on an increased incidence of renal tumours at high doses in a 2-year rat study. The transitional ADI was pending additional studies on carcinogenicity in mice and rats.
The previous health value was 0.03 mg/L (NHMRC and NRMMC 2004).
Health considerations
Metabolism: Chlorothalonil is absorbed via the gastrointestinal tract. It is largely eliminated in the faeces (95%) within 24 hours, with minor excretion of the parent compound or its metabolites in the urine. The major metabolite identified was 4-hydroxy-2,3,5-trichloroisophthalonitrile.
Acute effects: Chlorothalonil has low acute oral and dermal toxicity. Chlorothalonil is not a skin sensitiser.
Short-term effects: In a 90-day dietary study in mice and rats, kidney and liver weights were increased at doses of 71.4 and 75 mg/kg bw/day, respectively. The incidence of hyperplasia and hyperkeratosis of stomach epithelial cells was also increased at doses of 7.1 mg/kg bw/day and above in mice and at the lowest dose tested of 40 mg/kg bw/d and above (tested up to 1500 mg/kg bw/d) in rats. A separate medium-term dietary study in rats reported increased kidney weight at 3 mg/kg bw/day.
Long-term effects: Two-year dietary studies were conducted in mice, rats and dogs. The mouse study reported histopathological findings in the kidney at dose levels above 1.5 mg/kg bw. The rat study reported renal toxicity at 40 mg/kg bw/day. The dog study reported slight nephrotoxicity at 3 mg/kg bw. The overall NOEL was 1.5 mg/kg bw/day in the mouse and dog studies, and this was the basis for the ADI.
Carcinogenicity: There was evidence of carcinogenicity in both the mouse and rat studies. In mice, forestomach tumours occurred at 26 mg/kg bw/day as a result of increased hyperplasia and hyperkeratosis at 6 mg/kg bw/day and above. In rats, renal tumours and effects indicative of renal toxicity occurred at the lowest dose of 40 mg/kg bw/day. This dose level was considered well in excess of the likely level of human exposure.
Genotoxicity: There was equivocal evidence of genotoxicity from in vitro and in vivo short-term studies.
Reproductive and developmental effects: A 3-generation reproduction study in rats did not produce any evidence of reproductive effects. In developmental toxicity studies in rats and rabbits, there was evidence of maternotoxicity in rats and foetotoxicity in rabbits at dose levels well in excess of the likely level of human exposure.
Poisons Schedule: Chlorothalonil is included in Schedule 6 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 0.05 mg/L for chlorothalonil was determined as follows:
where:
1.5 mg/kg bw/day is the NOEL based on a long-term (2-year) dietary study in mice and dogs.
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.
100 is the safety factor applied to the NOEL derived from animal studies. This safety factor incorporates a factor of 10 for interspecies extrapolation and 10 for intraspecies variation.
The World Health Organization has not established a health-based guideline value for chlorothalonil and it is excluded from the list of agricultural chemicals guideline value derivation because it is “unlikely to occur in drinking water” (WHO 2004).
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.
Lambropoulou DA, Konstantinou IK, Albanis TA (2000). Determination of fungicides in natural waters using solid-phase microextraction and gas chromatography coupled with electron-capture and mass spectrometric detection. Journal of Chromatography A, 893(1):143-156.
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.
Ozhan G, Alpertunga B (2007). Determination of various fungicides in water by LC-DAD analysis. Fresenius Environmental Bulletin, 16(8):880-886.
Tomlin CD (ed) (2006). The Pesticide Manual: a world compendium, 14th Edition, British Crop Production Council, UK.
Walker AE, Holman RE, Leidy RB (2000). ELISA and GC/MS analysis of pesticide residues in North Carolina. Journal of the American Water Resources Association, 36(1):67-74.
WHO (World Health Organization) (2004). Guidelines for Drinking-water Quality. 3rd Edition, WHO, Geneva, Switzerland.
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