2,4-D [(2,4-Dichlorophenoxy) acetic acid]
(endorsed 2011)
Guideline
Based on human health concerns, 2,4-D in drinking water should not exceed 0.03 mg/L.
Related chemicals
2,4-D (CAS 94-75-7) belongs to the phenoxycarboxylic class of chemicals. Other pesticides in this class include dicloprop-p, MCPA, and mecoprop-p (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, 2,4-D 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: 2,4-D is a systemic herbicide used for the control of broad-leaf and aquatic weeds.
There are registered products containing 2,4-D in its various forms (free acid, alkali and amine salts and esters) in Australia. These products are intended for professional and home garden use and are used in food crops, in forestry, on turf and on non-crop land including industrial/commercial areas. They may be applied to these uses by a boom spray and aircraft. Data on currently registered products are available from the Australian Pesticides and Veterinary Medicines Authority.
Exposure sources: The main source of public exposure to 2,4-D is residues in food. Residue levels in food produced according to good agricultural practice are generally low.
The agricultural use of 2,4-D can involve direct application into waterways or sewage systems, which may then enter source waters for drinking water.
Typical values in Australian drinking water
Reported concentrations of 2,4-D in Queensland potable water supplies range from 0.2 to 0.0004 mg/L (0.4 µg/L) (Mitchell et al. 2005), and in Victoria range from 0.00002 to 0.34 mg/L (0.02 to 34 µg/L) (Amis 2008). Other river systems for which data exist have reported concentrations of up to 0.0156 mg/L (15.6 µg/L) (Hunter 2001).
Treatment of drinking water
Common water treatment processes are not effective in removing 2,4-D from water. Activated carbon adsorption, either powdered or granulated, is the method of choice for removing 2,4-D from drinking water supplies (Health Canada 1991). Powdered activated carbon removed 90% of an initial dose of 1.0 mg/L (Canadian Department of National Health and Welfare 1993). Laboratory tests or expert advice should be sought to ensure that an effective activated carbon is selected for use. Membrane filtration treatments, ultraviolet (UV) irradiation, ozone, and the combination of UV and peroxide are also effective in removing 2,4-D (Benitez et al. 2004).
Measurement
Residues of 2,4-D and its salts and esters in water are commonly measured by solid-phase extraction, chemical derivatisation, separation by liquid or gas chromatography and electron capture detection (WHO 2004). Analytical detection limits for this approach range from 0.00005 to 0.0005 mg/L (0.05 to 0.5 µg/L). High performance liquid chromatography with ultraviolet detector is also commonly used and can achieve a limit of detection (LOD) of 0.001 mg/L (1 µg/L). High performance liquid chromatography–mass spectrometry can reach a lower LOD (0.00001 mg/L [0.01 µg/L]). Measurement of 2,4-D is also described in EPA methods 515.1, 555.2, 555.3, 55.4, and 555 and ASTM International methods D5317-93 and D5317-98 (USEPA 2008). Enzyme-linked immunosorbent assay (ELISA) has been also used for the quantification of 2,4-D and its salts and typical reported LODs from immunoassays are 0.0001 to 0.0007 mg/L (0.1 to 0.7 µg/L) (USEPA 2008).
History of the health values
The current acceptable daily intake (ADI) for 2,4-D is 0.01 mg per kg of bodyweight (mg/kg bw), based on a no-observation-effect level (NOEL) of 1 mg/kg bw/day from a long-term (2-year) rat study. The NOEL is based on effects on the kidney. The ADI incorporates a safety factor of 100 and it was initially established in 1989 and re-confirmed in 2006.
An acute reference dose (ARfD) of 0.8 mg/kg bw/day was established for 2,4-D in 2006 based on a NOEL of 75 mg/kg bw/day derived from an acute exposure study in rats which reported effects on the nervous system. The ARfD incorporates a safety factor of 100.
The previous health value was 0.03 mg/L (NHMRC & NRMMC 2004).
Health considerations
Metabolism: Both the free acid and the salt form of 2,4-D are rapidly absorbed from the gastrointestinal tract and distributed to tissues, with highest concentrations in kidney, liver and brain. There is no evidence for accumulation in fat. More than 70% of the oral dose was recovered in urine in animals and humans.
Acute effects: 2,4-D has low acute oral and dermal toxicity, and is not a skin sensitizer.
Short-term effects: Three-month dietary studies in mice, rats and dogs reported effects on the kidney at dose levels of 45 mg/kg bw/day, 5 mg/kg bw/day and 3 mg/kg bw/day, respectively.
Long-term effects: Long-term dietary studies in rats reported abnormal kidney histopathology at doses of 5 mg/kg bw/day and above. Effects on the rat thyroid were also noted at 45 mg/kg bw/day. The NOEL of 1 mg/kg bw/day is the basis for the ADI.
Carcinogenicity: Based on long-term studies in mice, rats and dogs, there is no evidence of carcinogenicity for 2,4-D.
Genotoxicity: 2,4-D is not considered to be genotoxic, based on in vitro and in vivo short-term studies.
Reproductive and developmental effects: In a 2-generation reproduction study in rats, decreased offspring viability and malformations were seen only at maternotoxic doses. Developmental studies in rats and rabbits did not produce any evidence of effects on foetal development.
Neurotoxicity: In a 15-day dietary study, 2,4-D induced neurological effects that included changes in gait, coordination and decreased motor activity at doses of 250 mg/kg bw/day. The NOEL was 75 mg/kg bw/day and was the basis for the ARfD. These effects were not noted in other acute and/or repeat-dose studies in rats and dogs.
Poisons Schedule: 2,4-D is included in Schedule 5 or 6 of the Standard for the Uniform Scheduling of Medicines and Poisons No.1, 2010 (the Poisons Standard)(DoHA 2010)., depending on its concentration and use. Current versions of the Poisons Standard should be consulted for further information.
Derivation of health-based guideline
The health-based guideline of 0.03 mg/L for 2,4-D was determined as follows:
where:
1.0 mg/kg bw/day is the NOEL based on a long-term (2-year) 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.
This guideline value applies to 2,4-D as well as salts and esters of 2,4-D, as these are rapidly hydrolysed to the free acid in water.
The World Health Organization has established a health-based guideline value of 0.03 mg/L for 2,4-D in 1993 (WHO 2004).
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.
Amis A (2008). Survey of Pesticides in Surface Waters of Domestic Water Supplies – Victorian Water Authorities 1998–2007. Melbourne, Friends of the Earth Melbourne and National Toxics Network.
Canadian Department of National Health and Welfare (1993). Water treatment principles and applications: a manual for the production of drinking water. Canadian Water and Wastewater Association, Ottawa.
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.
Health Canada (1991). Guidelines for Canadian Drinking Water Quality – Technical Documents: 2,4-Dichlorophenoxyacetic Acid.
Hunter H, Sologinkin S, Choy S, Hooper A, Allen W, Raymond M, Peeters J (2001). Water management in the Johnstone Basin. Queensland Department of Natural Resources and Mines, Brisbane.
Mitchell C, Brodie J, White I (2005). Sediments, nutrients and pesticide residues in event flow conditions in streams of the Mackay Whitsunday Region, Australia. Marine Pollution Bulletin, 51(1-4):23-36.
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 (2008). Analytical Methods Approved for Drinking Water Compliance Monitoring of Organic Contaminants.
WHO (World Health Organization) (2004). Guidelines for Drinking-water Quality. 3rd Edition, WHO, Geneva, Switzerland.
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