Vernolate
(endorsed 2011)
Guideline
Based on human health concerns, vernolate in drinking water should not exceed 0.04 mg/L.
Related chemicals
Vernolate (CAS 1929-77-7) belongs to the thiocarbamate class of chemicals. Other pesticides in this class include EPTC, molinate, and pebulate (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, vernolate would not be a health concern unless the concentration exceeded 0.04 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 medium- to 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: Vernolate is a selective herbicide for the control of grasses and broad-leaf weeds in food-producing agricultural crops including soybeans, peanuts and potatoes.
There are currently no registered products that contain vernolate in Australia, but de-registered compounds may still be detected in water. Previously, products containing vernolate were intended for professional use and were available as concentrated solutions to be applied directly to soils in diluted form using ground, aerial or hand-held sprays.
Exposure sources: If used in the future, the main source of public exposure to vernolate and its metabolites would be residues in food. Residue levels in food produced according to good agricultural practice are generally be low.
Agricultural use of any vernolate in the future 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 published reports on vernolate occurrence in Australian drinking water supplies were found.
Treatment of drinking water
No specific data on the treatment of vernolate in drinking water have been identified.
Measurement
United States Environmental Protection Agency (USEPA) method 525.2 for the determination of organic compounds in drinking water by liquid-solid extraction and capillary column gas chromatography with mass spectrometry (GC-MS) can achieve a limit of quantitation (LOQ) of 0.047 μg/L to 0.14 μg/L for vernolate (USEPA 1995). Vernolate can be extracted from water by liquid-liquid extraction with dichloromethane and analysed by GC/MS in selected ion monitoring mode, with a LOQ of 0.5 μg/L. USEPA method 634 for the determination of thiocarbamate pesticides in industrial and municipal wastewaters by gas chromatography is also approved for the analysis of vernolate in water (USEPA 1993). USEPA method 507 for the determination of nitrogen and phosphorus containing pesticides in water by gas chromatography with a nitrogen-phosphorus detector can achieve a LOQ of 0.13 μg/L (Munch 1995). Solid-phase microextraction (SPME), followed by gas-liquid chromatography (GC) employing a nitrogen-phosphorus detector can achieve a LOQ of 0.1 μg/L, and SPME-GC employing mass spectrometry can achieve a LOQ of 0.02 μg/L (Choudhury et al. 1996).
History of the health values
The current acceptable daily intake (ADI) for vernolate is 0.01 mg per kg of bodyweight (mg/kg bw), based on a no-observed-effect level (NOEL) of 1 mg/kg bw/day from a reproduction study in rats. The NOEL is based on decreased bodyweight gain and food intake. The ADI incorporates a safety factor of 100 and it was first established in 1989.
The previous health value was 0.03 mg/L (NHMRC and NRMMC 2004).
Health considerations
Metabolism: Vernolate is rapidly absorbed via the gastrointestinal tract in rats. Metabolism is extensive, and proceeds through sulfoxidation. Excretion is primarily through urine in the form of conjugates and is complete by 7 days.
Acute effects: Vernolate has low acute oral and dermal toxicity. It is not a skin sensitiser.
Short-term effects: In 14-week dietary studies in rats and dogs, no effects were seen up to the highest doses tested, namely, 45 mg/kg bw/day in rats and 32 mg/kg bw/day in dogs.
Long-term effects: Long-term dietary studies were conducted in mice and rats. In mice, the only effects were changes in relative weights of kidney and liver at the highest dose tested, 100 mg/kg bw/day, and these were of doubtful toxicological significance. In rats, there was an increase in macrophage infiltration in lungs, and decreased bodyweight gain at the highest dose tested, 13 mg/kg bw/day. The lowest overall NOEL was 3.3 mg/kg bw/day in rats.
Carcinogenicity: Based on 2-year dietary studies in mice and rats, there is no evidence of carcinogenicity for vernolate.
Genotoxicity: Vernolate is not considered to be genotoxic, based on in vitro and in vivo short-term studies.
Reproductive and developmental effects: A 2-generation reproduction study in rats and developmental studies in mice and rabbits found no evidence of effects on reproductive parameters or foetal development. In the rat reproduction study, there was a decrease in parental food intake and an associated decrease in bodyweight gain at doses of 5 mg/kg bw/day and above in first generation parent animals. The NOEL of 1 mg/kg bw/day is the basis for the current ADI.
Neurotoxicity: A 35-day neurotoxicity study in hens found no evidence of delayed neurotoxicity at oral doses of 10 mg/kg bw.
Poisons Schedule: Vernolate is included in Schedule 5 of the Standard for the Uniform Scheduling of Medicines and Poisons No.1, 2010 (the Poisons Standard)(DoHA 2010). Current versions of the Poisons Standard should be consulted for further information.
Derivation of the health-based guideline
The health-based guideline of 0.04 mg/L for vernolate was determined as follows:
where:
1 mg/kg bw/day is the NOEL based on a 2-generation reproduction study in rats.
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.
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.
Choudhury TK, Gerhardt KO, Mawhinney TP (1996). Solid-phase microextraction of nitrogen- and phosphorus-containing pesticides from water and gas chromatographic analysis. Environmental Science and Technology, 30(11):3259–3265.
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.
Munch JW (1995). Method 507 Determination of Nitrogen and Phosphorus Containing Pesticides in Water by Gas Chromatography with a Nitrogen Phosphorus Detector. National Exposure Research Laboratory, Office of Research and Development, United States Environmental Protection Agency, Cincinnati, Ohio.
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.
Tomlin CD (ed) (2006). The Pesticide Manual: a world compendium, 14th edition, British Crop Production Council, UK.
USEPA (United States Environmental Protection Agency) (1993). Method 634. Methods for the Determination of Nonconventional Pesticides in Municipal and Industrial Wastewater. USEPA United States Environmental Protection Agency, Washington DC,
USEPA (United States Environmental Protection Agency) (1995). Method 525.2 Determination of Organic Compounds in Drinking Water by Liquid-Solid Extraction and capillarity Columns Gas Chromatography/Mass Spectrometry Revision 2.0. Environmental Monitoring Systems Laboratory Office of Research and Development, USEPA, Cincinnati, Ohio.
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