Haloxyfop
(endorsed 2011)
Guideline
Based on human health concerns, haloxyfop in drinking water should not exceed 0.001 mg/L.
Related chemicals
Haloxyfop (CAS 69806-34-4)(Haloxyfop-methyl (CAS 69806-40-2), Haloxyfop-P-methyl (CAS 72619-32-0) belongs to the aryloxyphenoxypropionate class of chemicals. Haloxyfop is a racemic mixture while haloxyfop-R is the resolved R-enantiomer (also known as haloxyfop-P) and has the greater herbicidal activity. It is used as the methyl ester. Other pesticides in this class include diclofop-methyl and diclofop-P-methyl (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, haloxyfop would not be a health concern unless the concentration exceeded 0.001 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: Haloxyfop is a post-emergence herbicide for the control of a wide range of annual and perennial grass weeds in a range of agricultural crops, including pasture and fruits as well as in forests.
There are registered products that contain haloxyfop in Australia. The products are intended for professional use and are available as concentrated solutions or wettable granules to be applied in diluted form using ground, aerial 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 haloxyfop are residues in food. Residue levels in food produced according to good agricultural practice are generally low.
Agricultural use of haloxyfop 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 data on the occurrence of haloxyfop in Australian waters were found.
Treatment of drinking water
No data on drinking water treatment removal efficiency were found for haloxyfop.
Measurement
Haloxyfop can be measured by routine liquid chromatography–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 haloxyfop is 0.0003 mg per kg body weight (mg/kg bw), based on a no-observed-effect level (NOEL) of 0.03 mg/kg bw/day from a long-term (2-year) dietary study in mice. The NOEL is based on the presence of liver tumours at 0.065 mg/kg bw/day. The ADI incorporates a safety factor of 100 and was established in 1987.
A health value has not been previously established by NHMRC.
Health considerations
Metabolism: Haloxyfop is rapidly absorbed via the gastrointestinal tract. In mice, male rats and dogs, the major excretion route is faeces, while in female rats, monkeys and humans, it is urine. Haloxyfop is not extensively metabolised and its half life varies from 24 hours in monkeys, to 1.8 days in mice, 6.3 days in humans, and 10 days in rats.
Acute effects: Haloxyfop has a low acute oral and dermal toxicity. It is not a skin sensitiser in guinea-pigs.
Short-term effects: Short-term studies have been performed in mice, rats, dogs and monkeys and indicate that the main target organ is the liver.
In a 4-day study in mice, haloxyfop caused liver enlargement from 10 mg/kg bw/day, and in a 14-day study in rats, there were hepatocellular hypertrophy and cytoplasmic changes at 30 mg/kg bw/day. Peroxisome proliferation in the liver was measured in 4-week dietary studies in mice and rats at 0.5 mg/kg bw/day and above. Liver effects were not noted in a 5-week dietary study in dogs, where haematological changes and increase in kidney weight were observed at 45 mg/kg bw/day.
A 13-week study in monkeys resulted in a dose-related increase in liver and kidney weights and decrease in thyroid weight from 10 mg/kg bw/day to 30 mg/kg/day.
Long-term effects: In a 2-year dietary study in mice, liver changes (increased liver weight and cytoplasmic alterations in both sexes, and increased alkaline phosphatase in males) were observed from 0.6 mg/kg bw/day. Liver tumours were noted from 0.065 mg/kg bw/day. The NOEL was 0.03 mg/kg bw/day, and this study is the basis for the ADI. In a 2-year dietary study in rats, changes in the liver (increased liver weight and clinical chemistry) were observed at 0.065 mg/kg bw/day. Kidney discolouration (increased pigment in the proximal convoluted tubules) and a decrease in haematological parameters were observed at 0.1 mg/kg bw/day at 6 months. Haematological parameters and liver weight were normal at the end of the study. A 1-year study in dogs showed decreased haematological values in males from 0.5 mg/kg bw/day.
Carcinogenicity: A 2-year dietary study in mice resulted in an increased incidence of liver adenomas and carcinomas from 0.065 mg/kg bw/day. Tumours were not noted in long-term studies in rats. The carcinogenic risk to humans is considered low, as the mice liver tumours are considered to be species-specific.
Genotoxicity: Only short-term in vitro studies are available, and based on these, haloxyfop is not considered to be genotoxic. There are no in vivo studies available.
Reproductive and developmental effects: A 2- and 3-generation reproduction study and developmental study in rats did not produce any evidence of effects on reproductive parameters or foetal development. In rabbits, there was a marginal increase in abnormalities and delayed development at maternotoxic dose levels that were well in excess of the likely level of human exposure.
Poisons Schedule: Haloxyfop 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 0.001 mg/L for haloxyfop was determined as follows:
where:
0.03 mg/kg bw/day is the NOEL based on a long-term (2-year) study in mice.
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.
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.
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