Etridiazole
(endorsed 2011)
Guideline
Based on human health concerns, etridiazole in drinking water should not exceed 0.1 mg/L.
Related chemicals
Etridiazole (CAS 2593-15-9) belongs to the thiazole fungicide class of chemicals. Other pesticides in this class include thiabendazole (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, etridiazole would not be a health concern unless the concentration exceeded 0.1 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: Etridiazole is a broad-spectrum fungicide used for the control of fungi contamination on seeds, roots and stems in turf crops, non fruit-bearing young trees, cotton and ornamental flower crops.
There are currently products registered in Australia that contain etridiazole. These products are intended for professional use. They are applied by spraying or direct incorporation into soil for cotton, non-food producing trees, turf, or ornamental flower crops. They are available as concentrated solutions to be applied in diluted form 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 source of public exposure to etridiazole and its metabolites is through residues on treated non-food crops, such as turf and flowers. Residue levels in crops produced according to good agricultural practice are generally low.
Agricultural use of etridiazole 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 published reports on etridiazole occurrence in Australian drinking water supplies were found. Estimated concentrations in groundwater from typical use of etridiazole on golf courses indicate that levels in groundwater are not likely to exceed 0.93 μg/L, and in surface water are not likely to exceed 32.3 μg/L for long-term exposure. Both these estimated concentrations are below guideline values indicating low concern (USEPA 2000).
Treatment of drinking water
No specific data on the treatment of etridiazole in drinking water have been identified.
Measurement
Etridiazole can be determined by solid-phase extraction followed by gas chromatography–mass spectrometry (USEPA Method 525.2). Typical limit of quantitation (LOQ) is 0.1 μg/L (Munch 1995). Continuous flow micro-extraction combined with high-performance liquid chromatography and ultraviolet detection can achieve a LOQ of <4 ng/mL (He et al. 2006).
History of the health values
The current acceptable daily intake (ADI) for etridiazole is 0.03 mg per kg of bodyweight (mg/kg bw), based on a no-observed-effect level (NOEL) of 2.9 mg/kg bw/day from a long-term (1-year dietary) study. The NOEL is based on decreased bodyweight gain and increased serum ALP activity in dogs. The ADI incorporates a safety factor of 100 and it was established in 1991. Before this, no ADI for etridiazole had been set in Australia.
The previous health value was 0.1 mg/L (NHMRC and NRMMC 2004).
Health considerations
Metabolism: Etridiazole is rapidly absorbed from the gastrointestinal tract, followed by wide tissue distribution, including body fat. It is extensively metabolised, with most of the compound excreted rapidly in urine as metabolites (>90% within 24 hours).
Acute effects: Etridiazole has low acute oral and dermal toxicity. It is not a skin sensitiser in guinea pig tests.
Short-term effects: Dietary studies in rats and dogs resulted in reduced bodyweight gain and increased liver weight, without associated change in histology, at dose levels of 35 mg/kg bw/day (rat) and 33 mg/kg bw/day (dog).
Long-term effects: Long-term dietary studies have been conducted in mice, rats and dogs and effects observed included reduced bodyweight gain, changes in organ weights relative to bodyweight, and effects on both thyroid and liver in the form of carcinomas. The lowest NOEL in these studies was 2.9 mg/kg bw/day in dogs. This NOEL forms the basis for the current ADI.
Carcinogenicity: An increased incidence of liver and thyroid tumours was observed in rats as a result of severe tissue irritation at the high dose (192 mg/kg bw/day). There was a clear threshold dose for this effect, which is not considered relevant at the low levels to which humans are exposed.
Genotoxicity: Etridiazole is not considered to be 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.
Poisons Schedule: Etridiazole 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 0.1 mg/L for etridiazole remains unchanged from the value established in 2004, and was determined as follows:
where:
2.9 mg/kg bw/day is the NOEL based on a long-term (2-year) dietary 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.
He Y, Lee HK (2006). Continuous flow microextraction combined with high-performance liquid chromatography for the analysis of pesticides in natural waters. Journal of Chromatography A, 1122(1-2):7-12.
Munch JW (1995). Method 525.2 Determination of Organic Compounds in Drinking Water by Liquid-Solid Extraction and capillarity Columns Gas Chromatography/Mass Spectrometry Revision 2.0. Cincinnati, Ohio, Environmental Monitoring Systems Laboratory Office of Research and Development USEPA.
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 (United States Environmental Protection Agency) (2000). R.E.D. Facts: Etridiazole (Terrazole). USEPA – Prevention, Pesticides And Toxic Substances (7508C).
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