Glyphosate
(updated 2011)
Guideline
Based on human health concerns, glyphosate in drinking water should not exceed 1 mg/L.
Related chemicals
Glyphosate (CAS 1071-83-6) is an aminophosphonic analogue of the natural amino acid glycine. It is available in a variety of salts, but is not chemically related to other pesticides (Tomlin 2006).
Human risk statement
With good water quality management practices, the exposure of the general population to glyphosate 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, glyphosate would not be a health concern unless the concentration exceeded 1 mg/L. Excursions above this level would need to occur over a significant period to be of 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: Glyphosate is a non-selective post-emergence herbicide used in the control of weeds in agriculture industry, forestry and public service areas including the aquatic environment.
There are many registered products containing glyphosate salts in Australia. Glyphosate products are intended for professional and home garden use, and are available as concentrated or ready-to-use solutions to be applied 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 glyphosate and its metabolites are the use of home garden products, and residues in food. Residue levels in food produced according to good agricultural practice are generally low.
Agricultural use of glyphosate 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
Glyphosate is generally not reported in analysis of Australian waters. It is strongly sorbed to soils but overseas studies show that there is potential for it to be present in waters as a result of over-spray or run-off from agricultural drainage ditches. For example, Netherlands surface waters were shown to contain up to 0.001 mg/L, and pond water in the USA was shown to contain up to 1.7 mg/L (IPCS 1994), demonstrating the high levels of contamination possible with some applications.
Treatment of drinking water
Glyphosate has been shown to be completely removed by ozonation (Bozkaya-Schrotter et al, 2008). Moderate removal can be achieved using powdered activated carbon adsorption.
Measurement
Glyphosate in Australian laboratories in commonly analysed by high performance liquid chromatography (HPLC) followed by post-column derivitisation using orthophthaldehyde and subsequent fluorescent detection (Eaglesham, personal communication). Some of the best equipped Australian laboratories are now using HPLC–tandem mass spectrometry for rapid and sensitive analysis without the need for derivitisation. Sensitivities for both procedures allow for low microgram per litre levels to be determined (Eaglesham, personal communication). The National Measurement Institute notes a limit of reporting of 0.01 mg/L.
History of the health values
The current acceptable daily intake (ADI) for glyphosate is 0.3 mg per kg of bodyweight (mg/kg bw), based on a no-observed-effect level (NOEL) of 30 mg/kg bw/day from a long-term (3-generation reproduction) study. This NOEL is based on no adverse effects observed at the highest dose in rats. The ADI incorporates a safety factor of 100 and was established in 1985.
The previous health value was 1.0 mg/L (NHMRC and NRMMC 2004).
Health considerations
Metabolism: Glyphosate has low absorption from the gastrointestinal tract (30-36%) in rats and rabbits. Dermal absorption is less than 5% in monkeys. It is essentially not metabolised, with 99% excreted in the urine as unchanged glyphosate.
Acute effects: Glyphosate has low acute oral and dermal toxicity. It is not a skin sensitiser.
Short-term effects: Three-month dietary studies in mice and dogs reported decreased bodyweight and food consumption at dose of 7500 mg/kg bw/day (mice) and 500 mg/kg bw/day (dogs).
Long-term effects: Long-term dietary studies in mice reported decreased bodyweight, hepatotoxicity, and changes in the urinary bladder and in the kidney at 814 mg/kg bw/day.
A long-term dietary study in dogs reported no significant toxicological effects up to the dose level of 45 mg/kg bw/day.
Carcinogenicity: Based on long-term studies in mice and rats, there is no evidence of carcinogenicity for glyphosate.
Genotoxicity: Glyphosate is not considered genotoxic, based on in vitro and in vivo short-term studies.
Reproductive and developmental effects: A 3-generation reproduction study in rats and developmental studies in rats and rabbits did not produce any evidence of reproductive effects, delayed development or teratogenicity at the dose levels up to 30 mg/kg bw/day. The ADI was based on the NOEL from this study, which was the highest dose tested (30 mg/kg bw/day).
A single-generation reproduction study in rats at doses up to 10 mg/kg bw/day reported no significant reproductive effects.
Poisons Schedule: Glyphosate 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 health-based guideline
The health-based guideline of 1 mg/L for glyphosate was determined as follows:
where:
30 mg/kg bw/day is the NOEL based on a 3-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.
The World Health Organization has not established a health-based guideline value for glyphosate and it is excluded from the list of agricultural chemicals guideline value derivation because “its health-based value is orders of magnitude higher than concentrations normally found in drinking-water” (WHO 2006).
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.
Bozkaya-Schrotter B, Daines C, Lescourret A, Bignon A, Breant P, Schrotter J (2008). Treatment of trace organics in membrane concentrates I: pesticide elimination, Water Science & Technology. Water Supply, 8(2):223-230.
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.
Eaglesham G (2009). Queensland Health Scientific Services, personal communication.
IPCS (Programme on Chemical Safety) (1994). Glyphosate. World Health Organisation Programme on Chemical Safety, Environmental Health Criteria, 159.
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.
WHO (World Health Organization) (2006). Guidelines for Drinking-water Quality. 3rd Edition, WHO, Geneva, Switzerland.
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