Simazine
(endorsed 2011)
Guideline
Based on human health concerns, simazine in drinking water should not exceed 0.02 mg/L.
Related chemicals
Simazine (CAS 122-34-9) belongs to the triazine class of chemicals. There are many other pesticides in this class, including atrazine and cyanazine (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, simazine would not be a health concern unless the concentration exceeded 0.02 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: Simazine is a pre- and post-emergent herbicide for the control of annual grasses and broad-leaf weeds in a range of agricultural crops such as in citrus, pomefruits, grapes, chickpeas and canola crops. It is also used as an algicide in swimming pools.
There are registered products that contain simazine in Australia. The products are intended for professional and home garden use and are available as concentrated solutions to be applied in diluted form using ground and aerial sprays directly onto soil, or added to swimming pools. Data on currently registered products are available from the Australian Pesticides and Veterinary Medicines Authority.
Exposure sources: The main sources of public exposure to simazine are residues in food and use in swimming pools. Residue levels in food produced according to good agricultural practice are generally low. The concentrations in swimming pools, when the product is used correctly, are also low.
Agricultural use of simazine 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 occurrence of simazine in Australian drinking water could be found. Simazine has been reported at 0.04 μg/L in the Brisbane River (Bengston Nash et al. 2006) and at levels as high as 18 μg/L in an agricultural drainage channel in New South Wales (Tran et al. 2007).
Levels of 1-2 μg/L have been reported in groundwater in the USA (WHO 2003). Simazine has also been reported in private and public drinking water supplies in Canada, with a maximum concentration of 23 μg/L (Health Canada 1986).
Treatment of drinking water
Chlorination, activated carbon or ozonation may be only partially effective at removing simazine from drinking waters, depending on precise operational conditions (Ormad et al. 2008).
Measurement
Simazine can be measured by routine gas 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 simazine 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 (2-year) dietary study in rats. The NOEL is based on decreased survival, decreased bodyweight gain, and evidence of anaemia. The ADI incorporates a safety factor of 100, and was established in 1990.
The previous ADI for simazine was set in 1985 at 0.003 mg/kg bw, based on a NOEL of 6 mg/kg bw/day from a 2-year study in rats and a safety factor of 2000.
The previous health value was 0.02 mg/L (NHMRC and NRMMC 2004).
Health considerations
Metabolism: Simazine is readily absorbed via the gastrointestinal tract, and is extensively metabolised via oxidative N-dealkylation to over 20 metabolites. The major metabolite is desethyl-desisopropyl-atrazine. Excretion in urine is rapid and almost complete within 24 hours.
Acute effects: Simazine has low acute oral and dermal toxicity. It is not a skin sensitiser.
Short-term effects: In a 2-week dietary study in rats, there was a dose-dependant increase in oestrous cycle length, as well as an increase in the plasma levels of the hormones prolactin, estradiol, and corticosterone at 5 mg/kg bw/day and above. No other effects were seen up to the highest dose tested of 15 mg/kg bw/day. Thirteen-week dietary studies in dogs reported vomiting, tremors and decreased bodyweight gain at doses of 75 mg/kg bw/day.
Long-term effects: Long-term dietary studies were conducted in mice, rats and dogs. In mice, no toxic effects were observed up to 100 mg/kg bw/day. In rats, there was decreased survival, decreased bodyweight gain, and evidence of anaemia, as well as early onset of mammary growths symptomatic of premature reproductive senescence, at 5 mg/kg bw/day and above. In dogs, there was decreased bodyweight gain, increases in liver enzymes and increased thyroid weight at 37.5 mg/kg bw/day. The lowest overall NOEL was 0.5 mg/kg bw/day in rats. This NOEL is the basis for the current ADI.
Carcinogenicity: In long-term rat studies, growths in mammary tissue were observed, however these changes were not considered relevant to humans. Therefore, based on 2-year studies in mice and rats, there is no evidence of carcinogenicity in humans from simazine.
Genotoxicity: Simazine is not considered to be genotoxic, based on in vitro and in vivo short-term studies.
Reproductive and developmental effects: A 2-generation reproduction study in rats and developmental studies in rats and rabbits did not produce any evidence for effects on reproductive parameters or foetal development.
Special studies on endocrine effects: Simazine was found to bind weakly to the estrogen receptor of rat uterine cells in vivo, but only at levels well in excess of the likely levels of human exposure.
Poisons Schedule: Simazine 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 simazine was determined as follows:
where:
0.5mg/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.
The World Health Organization has a health-based guideline value of 0.002 mg/L for simazine, incorporating an additional safety factor of 10 for possible non-genotoxic carcinogenicity (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.
Bengtson Nash SM, Goddard J, Müller JF (2006). Phytotoxicity of surface waters of the Thames and Brisbane River estuaries: a combined chemical analysis and bioassay approach for the comparison of two systems. Biosensors and Bioelectronics, 15:2086-2093.
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.
Ormad MP, Miguel N, Claver A, Matesanz JM, Ovelleiro JL (2008). Pesticides removal in the process of drinking water production. Chemosphere, 71:97-106.
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.
Tran ATK, Hyne RV, Doble P (2007). Determination of commonly used polar herbicides in agricultural drainage waters in Australia by HPLC. Chemosphere, 67:944-953.
WHO (World Health Organization) (2003) Simazine in Drinking-water; Background document for development of WHO Guidelines for Drinking-water Quality. WHO/SDE/WSH/03.04/42 WHO (World Health Organization) (2004). Guidelines for Drinking-water Quality. 3rd Edition, WHO, Geneva, Switzerland.
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