Diazinon

(endorsed 2011)

Guideline

Based on human health concerns, diazinon in drinking water should not exceed 0.004 mg/L.

Related chemicals

Diazinon (CAS 333-41-5) belongs to the organophosphate class of chemicals. There are many other pesticides in this class, including chlorpyrifos, malathion, and temephos (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, diazinon would not be a health concern unless the concentration exceeded 0.004 mg/L. Excursions above this level even for a short period are of concern as the health-based guideline is based on short-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: Diazinon is a insecticide used on sheep and cattle and companion animals; on fruit, vegetables, mushrooms and field crops; and in horticulture for nursery plants and ornamentals, including quarantine use. It is also used on lawns and turf, and in commercial, public and domestic buildings and surrounds.

There are registered products containing diazinon in Australia. These are intended for professional use and are available as soluble concentrates to be diluted and applied by ground and aerial sprays to crops, or as impregnated flea collars (pets) and ear tags (cattle). Data on currently registered products are available from the Australian Pesticides and Veterinary Medicines Authority.

Exposure sources: The main sources of public exposure to diazinon and its metabolites are its use in public or domestic buildings, in the garden, or on companion animals; and residues in food. Residue levels in food produced according to good agricultural practice are generally low.

Agricultural and veterinary use of diazinon 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 diazinon in Australian drinking waters have been identified.

Treatment of drinking water

Diazinon can be readily removed by various oxidation processes including ultraviolet radiation, oxidation, advanced oxidation and ozone (Real et al. 2007). However, oxidation can result in the formation of unwanted by-products, therefore a by-product management plan is also recommended before implementing any oxidation processes.

Activated carbon is effective in the removal of diazinon (Ohno et al. 2008). However, in the presence of chlorine, unwanted diazinon by-products were shown to desorb from the activated carbon surface (Ohno et al. 2008).

Nanofiltration has also been shown to be effective in the removal of Diazinon (Kiso et al. 2000).

Measurement

The practical limit of quantification for diazinon in water is 0.0001 µg/L by liquid chromatography–tandem mass spectrometry (Alder et al. 2006).

History of the health values

The current acceptable daily intake (ADI) for diazinon is 0.001 mg per kg of bodyweight (mg/kg bw), based on a no-observable-effect level (NOEL) of 0.02 mg/kg bw/day from a short-term (37-43 days) human study. The NOEL was based on inhibition of plasma cholinesterease. The ADI incorporates a safety factor of 20 and was established in 1999.

The acute reference dose (ARfD) of 0.01 mg/kg bw/day for diazinon was established in 2002, based on a NOEL of 0.2 mg/kg bw/day from a human study. The NOEL was based on red blood cell cholinesterase inhibition after a single dose of diazinon. The ARfD incorporates a safety factor of 20.

The previous health value was 0.003 mg/L (NHMRC and NRMMC 2004).

Health considerations

Metabolism: Diazinon is rapidly absorbed from the gastrointestinal tract, extensively metabolised and rapidly excreted mainly in urine (97%) within 24 hours. The highest tissue concentrations are in fat, with no evidence of accumulation.

Acute effects: Diazinon has moderate acute oral and dermal toxicity, and is a skin sensitiser in guinea pigs. It can also cause delayed neuropathy 24-96 hours after acute exposure. Clinical symptoms of toxicity were typical of cholinesterase inhibition and included tremors, prostration, coma, piloerection, ataxia, and salivation.

Short-term effects: Short-term dietary studies in rats reported inhibition of plasma cholinesterase at doses of 0.2 mg/kg bw/day. Inhibition of erythrocyte cholinesterase activity was seen at 2.5 mg/kg bw/day, while brain cholinesterase activity was inhibited at 23 mg/kg bw/day. In a 37-43 day dietary study in humans, the NOEL for cholinesterase inhibition was 0.02 mg/kg/ bw/day, and this is the basis for the ADI.

Long-term effects: In long-term dietary studies in rats, mice and dogs, plasma cholinesterase inhibition was seen at doses of 0.018 mg/kg bw/day and above (dogs). Decreased brain cholinesterase activity (rats) and decreased bodyweight gain (dogs) was seen at 5 mg/kg bw/day. Clinical symptoms of nervous system toxicity were seen at 15 mg/kg bw/day (mice). The overall lowest NOEL was 0.0037 mg/kg bw/day (dogs) in these studies.

Carcinogenicity: Based on long-term studies in mice, rats and dogs, there is no evidence of carcinogenicity for diazinon.

Genotoxicity: Diazinon is not considered to be genotoxic, based on in vitro and in vivo short term studies.

Reproductive and developmental effects: Reproduction studies in rats and developmental studies in rats and rabbits produced no evidence of effects on reproductive parameters or on foetal development.

Poisons Schedule: Diazinon 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 the health-based guideline

The health-based guideline value of 0.004 mg/L for diazinon was determined as follows:

$$\text{ 0.004 mg/L } = \dfrac{\text{ 0.02 mg/kg bodyweight/day x 70 kg x 0.1 }}{\text{ 2 L/day x 20 }}$$

where:

• 0.02 mg/kg bw/day is the NOEL based on a short-term (37-43 day) repeat-dose study in humans.

• 70 kg is taken as the average weight of an adult.

• 0.1 is a proportionality factor based on the conservative 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.

• 20 is the safety factor applied to the NOEL from a study conducted in humans. The safety factor of 20 incorporates a factor of 10 for intraspecies variation and 2 for the closeness of the NOEL and LOEL.

The World Health Organization has not established a health-based guideline value for diazinon and it is excluded from the list of agricultural chemicals guideline value derivation because it is “unlikely to occur in drinking water” (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.

Alder L, Greulich K, Kempe G, Vieth B (2006). Residue analysis of 500 high priority pesticides: better by GC-MS or LC-MS/MS? Mass Spectrometry Reviews, 25(6):838-65.

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.

Kiso Y, Nishimura Y, Kitao T, Nishimura K (2000). Rejection properties of non-phenylic pesticides with nanofiltration membranes. Journal of Membrane Science, 171, 229-237.

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.

Ohno K, Minami T, Matsui Y, Magara Y (2008). Effects of chlorine on organophosphorus pesticides adsorbed on activated carbon: Desorption and oxon formation. Water Research, 42, 6-7, 1753-1759.

Real FJ, Benitez FJ, Acero JL, Gonzalez M (2007). Removal of diazinon by various advanced oxidation processes. Journal of Chemical Technology and Biotechnology, 82:566-574.

Tomlin CD (ed) (2006). The Pesticide Manual: a world compendium, 14th Edition, British Crop Production Council, UK.

WHO (World Health Organization) (2004). Guidelines for Drinking-water Quality. 3rd Edition, WHO, Geneva, Switzerland.