Pebulate
(endorsed 2011)
Guideline
Based on human health concerns, pebulate in drinking water should not exceed 0.03 mg/L.
Related chemicals
Pebulate (CAS 1114-71-2) belongs to the thiocarbamate class of chemicals. Other pesticides in this class include molinate, butylate, and EPTC (ethyl dipropylthiocarbamate) (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, pebulate would not be a health concern unless the concentration exceeded 0.03 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: Pebulate is a selective herbicide for the control of grassy weeds in tobacco and tomato crops.
There is at least one registered product containing pebulate in Australia. Pebulate products are intended for professional use and are available as a concentrated solution to be applied in diluted form by roller application to foliage, and by boomspray to soil. Data on currently registered products are available from the Australian Pesticides and Veterinary Medicines Authority.
Exposure sources: The main sources of public exposure to pebulate and its metabolites are residues in food and in tobacco used for cigarettes and cigars. Residue levels in food and tobacco produced according to good agricultural practice are generally low.
Agricultural use of pebulate 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 pebulate occurrence in Australian drinking water supplies were found.
Treatment of drinking water
No specific data on the treatment of pebulate in drinking water have been identified.
Measurement
United States Environmental Protection Agency method 525.2 (USEPA 1995) for the determination of organic compounds in drinking water by liquid-solid extraction and capillary column gas chromatography–mass spectrometry (GC-MS) can achieve a limit of quantitation (LOQ) of 0.08 µg/L to 0.11 µg/L for pebulate. Pebulate 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 pebulate in water (USEPA 1993). USEPA method 507 for the determination of nitrogen and phosphorus containing pesticides in water by gas chromatograpy (GC) with a nitrogen-phosphorus detector can achieve a LOQ of 0.05 µg/L (Munch 1995). Solid-phase microextraction (SPME) followed by gas–liquid chromatography employing a nitrogen-phosphorus detector can achieve a LOQ of 0.04 µg/L, and SPME-GC employing mass spectrometry can achieve a LOQ of 0.01 µg/L (Choudhury et al. 1996).
History of the health values
The current acceptable daily intake (ADI) for pebulate is 0.007 mg per kg of bodyweight (mg/kg bw), based on no-observed-effect levels (NOELs) of 0.7 and 0.75 mg/kg bw/day from a long-term dietary study and a reproduction study in rats, respectively. The NOELs are based on decreased bodyweight and slight lens disjunction in eyes at 7 mg/kg bw/day in the long-term study, and decreased bodyweight in parents and offspring at 7.5 mg/kg bw/day in the reproduction study. The ADI incorporates a safety factor of 100, and was established in 1990.
The previous ADI of 0.01 mg/kg bw was set in 1982.
The previous health value was 0.03 mg/L (NHMRC and NRMMC 2004).
Health considerations
Metabolism: Pebulate was rapidly absorbed and extensively metabolised in oral dosing studies in rats. Excretion was mainly through expired air and to a lesser extent by urine and faeces, and was complete by 24 hours. The major metabolites were mercapturic acids.
Acute effects: Pebulate has low acute oral and dermal toxicity. Pebulate is not a skin sensitiser.
Short-term effects: In medium-term dietary studies in rats and dogs, there was reduced cholinesterase activity in brain and red blood cells, as well as reduced red blood cell count, at doses of 16 mg/kg bw/day.
Long-term effects: Long-term studies were conducted in rats (2-years) and dogs (1-year). In rats, there was decreased bodyweight and slight lens disjunction in the eyes at doses of 7 mg/kg bw/day. In dogs, minor decreases in bodyweight and increases in serum platelet count were seen at doses of 50 mg/kg bw/day. The overall NOEL was 0.7 mg/kg bw/day in the rat study, which is partly the basis for the ADI.
Carcinogenicity: Based on a 2-year study in mice and rats, there is no evidence of carcinogenicity for pebulate.
Genotoxicity: Only short-term in vitro studies are available; these report no evidence that pebulate is genotoxic.
Reproductive and developmental effects: A two-generation study in rats found no effects on reproductive parameters. Decreased bodyweights in parents and offspring were seen at doses of 7.5 mg/kg bw/day. The NOEL was 0.75 mg/kg bw/day, which is partly the basis for the ADI. Development studies in rats and rabbits found no effects on foetal development.
Poisons Schedule: Pebulate is included in Schedule 6 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 0.03 mg/L for pebulate was determined as follows:
where:
0.7 mg/kg bw/day is the NOEL based on a 2-generation studies and long-term (2-year) dietary studies in rats. The effects at higher levels were decreased bodyweights and lens disjunction.
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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