Diuron
(endorsed 2011)
Guideline
Based on human health concerns, diuron in drinking water should not exceed 0.02 mg/L.
Related chemicals
Diuron (CAS 330-54-1) belongs to the urea class of chemicals. Other pesticides in this class include fluometuron, linuron, methabenzthiazuron, siduron and tebuthiuron (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, diuron would not be a health concern unless the concentration exceeded 0.02 mg/L. Excursions above this level even for a relatively short period are of concern as the health-based guideline is based on medium-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: Diuron is a herbicide used for the control of broad-leaf weeds and grasses on a variety of crops including citrus, pineapple, cereals and sugar cane, as well as around buildings and public rights of way. It is also used as a defoliant on cotton, in marine antifouling paints and in ponds and aquariums to control algae.
There are registered products containing diuron in Australia. These are intended for professional and home garden use and contain diuron alone or in combination with other active ingredients. The products are generally available as suspension concentrates and water dispersible granules to be mixed with water and applied by aerial or ground sprayers. Data on currently registered products are available from the Australian Pesticides and Veterinary Medicines Authority.
Exposure sources: The main sources of public exposure to diuron are the use of home garden products, entry into treated public areas, and residues in food. Residue levels in food produced according to good agricultural practice are generally low.
Agricultural use of diuron may potentially lead to contamination of source waters through processes such as run-off, spray drift or entry into groundwater, or through the discharge of treated aquarium or pond water.
Typical values in Australian drinking water
No reports of diuron in Australian drinking waters have been identified.
Treatment of drinking water
Diuron has been shown to be completely removed from water by chlorination when the chlorine dose is adjusted to match chlorine demand (Ormad et al. 2008). Ozonation and activated carbon adsorption for diuron removal has also been reported with high-moderate success (Bozkaya-Schrotter et al. 2008, Ormad et al. 2008). Advanced oxidation using ultraviolet irradiation and peroxide has been demonstrated to achieve a moderate level of diuron removal (Kruithof et al. 2002). Conventional coagulation/floculation has been shown to provide a relatively low removal rate (30%).
Measurement
Diuron can be measured in drinking water by solid phase extraction followed by high performance liquid chromatography with tandem mass spectrometry. The limit of quantitation for this method is typically 0.01 µg/L (QHFSS 2008).
History of the health values
The current acceptable daily intake (ADI) for diuron is 0.007 mg per kg of bodyweight (mg/kg bw), based on a no-observed-effect level (NOEL) of 0.7 mg/kg bw/day from a 6-month dietary study in rats. This NOEL is based on reduced haemoglobin concentrations and increased reticulocytes. The ADI incorporates a safety factor of 100 and it was established in 2005.
The previous ADI, established in 1987, was 0.006 mg/kg bw based on a NOEL of 0.6 mg/kg bw/day from a 2-year dog study. The NOEL was based on abnormal blood pigments (probably sulfaemoglobin).
The acute reference dose (ARfD) of 0.007 mg/kg bw/day for diuron was established in 2005, based on a NOEL of 0.7 mg/kg bw/day from a 6-month dietary study in rats, as indicated above. The ARfD incorporates a safety factor of 100.
The previous health value was 0.03 mg/L, with a note that this pesticide has either been detected on occasions in Australian drinking water or its likely use would indicate that it may occasionally be detected (NHMRC and NRMMC 2004).
Health considerations
Metabolism: Diuron is rapidly and extensively absorbed from the gastrointestinal tract. It is efficiently metabolised and excreted within the first 24 hours. The main metabolites detected in blood and urine are 3-(3,4-dichlorophenyl)-1-methyl urea, 3-(3,4-dichlorophenyl) urea and 3,4-dichloroaniline.
Acute effects: Diuron has low acute oral and dermal toxicity in rats. It is not a skin sensitiser.
Short-term effects: Short-term dietary studies in rats reported changes to haematological parameters consistent with haemolytic anaemia at dose levels of 1.6 mg/kg bw/day in males and 1.8 mg/kg bw/day in females. Other effects included changes indicative of liver and kidney damage. The NOEL of 0.7 mg/kg bw/day in rats is the basis for the current ADI.
Long-term effects: Long-term dietary studies have been conducted on mice, rats and dogs. These studies reported findings of haemolytic anaemia at 3.1 mg/kg bw/day and above in a 2-year dog study. Other findings included liver enzyme level and organ weight increases and histological changes in liver, spleen and kidney, rats at 1 mg/kg bw/day and dogs at 7.5 mg/kg bw/day and above.
Carcinogenicity: The long-term study in rats reported an increased incidence of tumours in the bladder epitheliu; however, development of these tumours in rats appeared to be related to urinary pH changes as a result of feeding the rats a specific rat diet, rather than to diuron alone, and are therefore not considered to be relevant to humans.
Genotoxicity: Diuron is not considered to be genotoxic, based on in vitro and in vivo short-term studies.
Reproductive and developmental effects: A reproduction study in rats with diuron reported no changes in reproductive parameters. Developmental toxicity studies in rats and rabbits reported decreased foetal bodyweight only at above maternotoxic dose levels.
Poisons Schedule: Diuron 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 0.02 mg/L for diuron was determined as follows:
where:
0.7 mg/kg bw/day is the NOEL based on a medium-term (6-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. The safety factor of 100 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.
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.
Kruithof J, Kamp P, Belosevic M (2002). UV/H2O2 treatment: the ultimate solution for pesticide control and disinfection. Water Science Technology: Water Supply, 2(1):113-122.
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.
Ormad MP, Miguel N, Claver A, Matesanz JM, Ovelleiro JL (2008). Pesticides removal in the process of drinking water production. Chemosphere, 71:97–106.
QHFSS (Queensland Health Forensic and Scientific Services) (2008). Personal Communication.
Tomlin CD (ed) (2006). The Pesticide Manual: a world compendium, 14th Edition, British Crop Production Council, UK.
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