Picloram
(endorsed 2011)
Guideline
Based on human health concerns, picloram in drinking water should not exceed 0.3 mg/L.
Related chemicals
Picloram (CAS 2545-60-0) belongs to the pyridinecarboxylic acid class of chemicals. Other pesticides in this class include clopyralid, fluroxypyr and triclopyr (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, picloram would not be a health concern unless the concentration exceeded 0.3 mg/L. Excursions above this level over a short to medium period are of concern, as the health-based guideline is based on effects observed in a 3-month study.
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: Picloram is a post-emergent herbicide for the control of woody and herbaceous weeds and rhizomatous plants in cereal crops, conservation areas, reserves and parks, and in home gardens.
There are registered products that contain picloram as an ester or a salt in Australia. The products are intended for professional and home garden use. They are generally available as emulsifiable concentrates that are applied by aerial and ground spray, or by direct brushing onto foliage or pouring into the trunks of herbaceous and woody weeds. Data on currently registered products are available from the Australian Pesticides and Veterinary Medicines Authority.
Exposure sources: The main sources of public exposure to picloram and its metabolites are the use of home garden products, contact with treated weeds in parklands, and residues in food. Residue levels in food produced according to good agricultural practice are generally low.
The use of picloram in parkland areas and agriculture 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 picloram in Australian drinking waters have been identified.
Treatment of drinking water
Picloram is completely removed when water undergoes advanced oxidation with iron catalysed ultraviolet irradiation and peroxide (Fenton reaction) (Huston and Pignatello 1999). More research into the removal of picloram is recommended.
Measurement
Picloram may be measured in drinking waters by liquid chromatography–mass spectrometry, with a typical detection limit of 0.01 µg/L (QFSS 2009 pers comm).
History of the health values
The current acceptable daily intake (ADI) for picloram is 0.07 mg per kg of bodyweight (mg/kg bw), based on a no-observed-effect level (NOEL) of 7 mg/kg bw/day from a short-term (3-month) dietary study in dogs. The NOEL is based on increased liver weight. The ADI incorporates a safety factor of 100 and was first established in 1987.
The previous health value was 0.3 mg/L (NHMRC and NRMMC 2004).
Health considerations
Metabolism: Picloram is readily absorbed in the gastrointestinal tract. It is not extensively metabolised, and is rapidly excreted in the urine, almost completely within 48 hours.
Acute effects: Picloram and its esters and salts have low acute oral dermal toxicity. There is some evidence that picloram is a skin sensitiser in humans. Picloram esters and salts are skin sensitisers in guinea pigs.
Short-term effects: A 3-month oral toxicity study conducted in rats reported no adverse effects up to maximal levels of exposure relevant to humans. A 6-month dietary study in dogs reported increased liver weight at 35 mg/kg bw/day. The lowest overall NOEL was 7 mg/kg bw/day in dogs. This NOEL is the basis for the current ADI.
Long-term effects: Long-term dietary studies were conducted in rats and dogs. In both rats and dogs, the studies reported increases in liver weight, hepatocellular enlargement, and liver discolouration at doses of 60 mg/kg bw/day and above. The lowest overall NOEL was 20 mg/kg bw/day in the rat.
Carcinogenicity: There is limited evidence of picloram (technical grade) carcinogenicity in rats.
Genotoxicity: Picloram is not considered to be genotoxic, based on in vitro and in vivo short-term studies.
Reproductive and developmental effects: Two- and 3-generation reproduction studies in rats and developmental studies in rats and rabbits did not produce any evidence of effects on reproductive parameters or foetal development.
Poisons Schedule: Picloram is considered not to require control by scheduling due to its low toxicity and is therefore included in Appendix B 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 0.3 mg/L for picloram was determined as follows:
where:
7 mg/kg bw/day is the NOEL based on a medium-term (3-month) dietary 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.
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.
Huston PL, Pignatello JJ (1999). Degradation of selected pesticide active ingredients and commercial formulations in water by the photo-assisted Fenton reaction 1999. Water Research, 33(5):1238-1246.
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.
QFSS (Queensland Forensic and Scientific Services) (2009). Personal communication.
Tomlin CD (ed) (2006). The Pesticide Manual: a world compendium, 14th Edition, British Crop Production Council, UK.
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