Triclopyr
(endorsed 2011)
Guideline
Based on human health concerns, triclopyr in drinking water should not exceed 0.02 mg/L.
Related chemicals
Triclopyr (CAS 55335-06-3) belongs to the pyridinecarboxylic acid class of chemicals. Other pesticides in this class include chlopyralid, fluroxypyr and picloram (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, triclopyr would not be a health concern unless the concentration exceeded 0.02 mg/L. 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: Triclopyr is a post-emergence herbicide for the control of woody and broad-leaf weeds in commercial and industrial areas, native pastures, right of ways, forests, fence lines and in the home garden.
There are registered products that contain triclopyr, its triethylamine salt or butoxyethyl ester in Australia. The products are intended for professional and/or home garden use. Products are available as a concentrated solution to be applied directly to weeds as a dilute spray by hand-held, mistblower, boom and aerial application methods. Data on currently registered products are available from the Australian Pesticides and Veterinary Medicines Authority.
Exposure sources: The main source of public exposure to triclopyr and its metabolites is the use of home garden products. A further possible source of exposure is residues in food from livestock grazing in treated areas. Residue levels in food produced according to good agricultural practice are generally low.
Commercial use of triclopyr may potentially lead to contamination of source waters through processes such as run-off, spray drift or entry into groundwater.
Reported values in Australian waters
No data on occurrence of triclopyr in Australian waters could be found. In the USA, the United States Environmental Protection Agency predicts that triclopyr will not reach high concentrations in groundwater, and concludes that it is not a concern in drinking water that is derived from groundwater. Triclopyr is also not expected to be present in significant concentrations in surface water due to its quick degradation (USEPA 1998).
Typical values in Australian drinking water
No information could be found on the efficiency of drinking water treatment processes in removing triclopyr.
Measurement
Triclopyr can be measured by routine gas chromatography with mass spectrometry analysis, with a limit of reporting of 0.01 µg/L (Queensland Health 2007).
History of the health values
The current acceptable daily intake (ADI) for triclopyr is 0.005 mg per kg of bodyweight (mg/kg bw), based on a no-observed-effect level (NOEL) of 0.5 mg/kg bw/day from a long-term dietary study in dogs. The NOEL is based on histopathological changes in the kidney. The ADI incorporates a safety factor of 100 and was established in 1986.
The previous health value was 0.01 mg/L (NHMRC and NRMMC 2004).
Health considerations
Metabolism: Triclopyr is readily and extensively absorbed via the gastrointestinal tract in animals and humans. It is not extensively metabolised, and the majority of the dose is excreted unchanged in the urine within 72 hours.
Acute effects: Triclopyr has moderate acute oral toxicity and low acute dermal toxicity. It is a skin sensitiser.
Short-term effects: Short-term dietary studies conducted in mice, rats and dogs reported the kidney to be the most sensitive target organ. Studies in mice and rats reported changes in relative kidney weights together with histopathological changes in the kidney at doses of 20 mg/kg bw/day and above. At 70 mg/kg bw/day in rats, there was an increase in relative liver weights and decreased bodyweight gain, as well as some evidence of necrosis of hepatocytes. In dogs, there was evidence of decreased renal function at doses of 2.5 mg/kg bw/day and above.
Long-term effects: Long-term dietary studies conducted in mice, rats and dogs reported the liver and kidneys to be the main target organs. A 2-year study in mice reported decreased bodyweight gain, and clinical chemistry changes indicative of kidney and liver damage, together with histopathological effects in the bladder, liver and kidneys, at doses of 25.5 mg/kg bw/day and above.
A 2-year study in rats reported increased absolute and relative kidney weights and histopathological effects in the kidney at doses of 12 mg/kg bw/day and above.
A 1-year dog study reported evidence of decreased renal function together with histopathological changes in the kidney at doses of 2.5 mg/kg bw/day and above. The NOEL from this study was 0.5 mg/kg bw/day and this is the basis of the current ADI.
Carcinogenicity: Based on long-term studies in mice, rats and dogs, there is no evidence of carcinogenicity for triclopyr.
Genotoxicity: Triclopyr is not considered to be genotoxic, based on in vitro and in vivo short-term studies.
Reproductive and developmental effects: Two and three-generation reproductive studies in rats and developmental studies in rats and rabbits did not produce any evidence of effects on reproductive parameters or foetal development, other than maternal toxicity at high dose levels that were well in excess of the likely level of human exposure.
Poisons Schedule: Triclopyr 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 0.02 mg/L for triclopyr was determined as follows:
where:
0.5 mg/kg bw/day is the NOEL based on a long-term (1-year) study in 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.
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.
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.
Queensland Health (2007). Organochlorine, organophosphorous and synthetic pyrethroid pesticide, urea and triazine herbicides and PCBs in water. QHFSS SOP 16315.
Tomlin CD (ed) (2006). The Pesticide Manual: a world compendium, 14th edition, British Crop Production Council, UK.
USEPA (United States Environmental Protection Agency) (1998). Reregistration eligibility decision (RED) for triclopyr. EPA 738-R-98-011. USEPA.
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