Propazine
(endorsed 2011)
Guideline
Based on human health concerns, propazine in drinking water should not exceed 0.05 mg/L.
Related chemicals
Propazine (CAS 139-40-2) belongs to the triazine class of chemicals. There are many pesticides in this class, including atrazine, symazine 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, propazine would not be a health concern unless the concentration exceeded 0.05 mg/L. Minor excursions above this level would need to occur over a relatively long period to be a health 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: Propazine is a herbicide used for the control of broad-leaf weeds in agricultural crops.
There are currently no products containing propazine registered in Australia, but de-registered conpounds may still be detected in water.
Exposure sources: The main source of public exposure to propazine and its metabolites is residues in food. Residue levels in food produced according to good agricultural practice are generally low.
Agricultural use of propazine 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 reports of propazine in Australian drinking waters have been identified.
Treatment of drinking water
Relatively high removal rates of propazine have been achieved using conventional flocculation, adsorption onto activated carbon and ozonoation (Ormad et al. 2008). More research into the reliable removal of propazine is recommended. If propazine is detected, jar testing with a matrix of multiple oxidants, adsorbents, and coagulants is recommended.
Measurement
Analysis for propazine in drinking water now typically employs solvent extraction or solid phase extraction with gas chromatography-mass spectrometry determination (QHFSS, 2009 pers comm). Limits of detection are normally 10 ng/L using this methodology.
History of the health values
The current acceptable daily intake (ADI) for propazine is 0.02 mg per kg of bodyweight (mg/kg bw), based on a no-observed-effect level (NOEL) of 1.5 mg/kg bw/day from a medium-term (90-day) dog study. The NOEL is based on reduced bodyweight gain. The ADI incorporates a safety factor of 100, and was established in 1986.
The previous health value was 0.05 mg/L (NHMRC and NRMMC 2004).
Health considerations
Metabolism: No metabolism studies are available for propazine.
Acute effects: Propazine has low acute oral and dermal toxicity. It is not a skin sensitiser in guinea pig.
Short-term effects: Medium-term (3-month) dietary studies have been conducted in rats and dogs. Decreased bodyweight gain and food consumption was observed in rats at doses of 14 mg/kg bw/day and above, and in dogs at doses of 6 mg/kg bw/day and above. At higher doses, effects on biochemical and haematological parameters as well as changes in urinalysis and histopathology, and increased mortality were reported in both rats and dogs. The lowest overall NOEL was 1.5 mg/kg bw/day based on decreased bodyweight gain in dogs, and this is the basis for the current ADI.
Long-term effects: In long-term studies in mice and rats, the most sensitive toxicological effect was decreased bodyweight gain and food consumption. A long-term dietary study in mice reported decreased food consumption and a slight increase in mortality at 480 mg/kg bw/day and above. In a 2-year rat study, decreased bodyweight gain and food consumption were observed at doses of 60 mg/kg bw/day and above. The NOEL for this study was 6 mg/kg bw/day.
Carcinogenicity: There was some evidence of carcinogenicity in rats; however, the mode of action is not considered relevant to humans at the normal levels of human exposure.
Genotoxicity: Only short-term in vitro studies are available; these report no evidence that propazine is genotoxic.
Reproductive and developmental effects: A 3-generation reproduction study in rats and developmental studies in rats did not produce any evidence of effects on reproductive parameters or on the developing foetus.
Poisons Schedule: Propazine is not included in 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 0.05 mg/L for propazine was determined as follows:
where:
1.5 mg/kg bw/day is the NOEL based on a short-term (3-month) study in dogs.
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.
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) (2009). Personal communication.
Tomlin CD (ed) (2006). The Pesticide Manual: a world compendium, 14th Edition, British Crop Production Council, UK.
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