Diazinon Chemical Review

In December 1996 the APVMA (then the NRA) began a review of diazinon because of concerns over its potential to form highly toxic breakdown products, particularly if the chemical were exposed to a small amount of water. Other concerns related to diazinon’s potential to pose a risk to public health, occupational health and safety, the environment and animals, and the impact of diazinon residues on Australia’s trade.

In February 2000, the NRA Expert Panel on Organophosphate (OP) Sheep Dips reviewed the findings of the United Kingdom Institute of Occupational Medicine report, Epidemiological study of the relationship between exposure to organophosphate pesticides and indices of chronic peripheral neuropathy, and neuropsychological abnormalities in sheep farmers and dippers (July 1999). The panel concluded that work practices and exposure risks differed between Australia and the United Kingdom. However, the panel could not completely rule out a link between OP exposure and long-term effects. The panel recommended reducing worker exposure to OPs and that the APVMA (then the NRA) review the uses of OPs on sheep. Those recommendations of the panel that have direct implications for the review of diazinon will be incorporated in the review outcomes.

This review is separate from, but related to, the review of selected sheep ectoparasiticides. While the review of diazinon will be conducted separately, the outcomes of this review maybe taken into consideration in finalising related reviews.

The APVMA selected diazinon for review after scoring diazinon highly against all the agreed selection criteria for public health, occupational health and safety, residues and environment. In summary, the concerns over diazinon were:

• reported incidents of human poisoning from use of products containing diazinon
• potential acute toxicity risk
• possible long-term effects on users exposed to diazinon over a period of time
• detection of toxic breakdown products in registered products
• reports of small animal fatalities due to toxic breakdown products
• groundwater contamination
• reported incidents of bird kills in Australia
• United States Environmental Protection Agency (EPA) regulatory action to partially restrict uses based on its toxicity to birds and aquatic species
• lack of appropriate maximum residue limits (MRLs) for agricultural and horticultural uses
• residue detections in export produce above MRLs
• MRL inconsistencies with major trading partners (United States, Canada, Codex).

While the selection process ranked diazinon highly due to certain issues, the review was not confined only to those issues, but covered all aspects of registration and approval of diazinon. The review included registrations of products containing diazinon and associated label and active constituent approvals. The scope was expanded for the 2006 Diazinon preliminary review findings, part 2, to include registered uses on sheep, cattle, pigs, goats and horses after new information was provided to the APVMA.

In 2002 the NRA released the revised diazinon draft report and component assessment reports for residues, chemistry, agriculture, toxicology, occupational health and safety and the environment.

In 2003 the NRA released the review findings report for diazinon, part 1, which contained the final component assessment report for chemistry.

In 2006 the APVMA released the diazinon preliminary review findings report, part 2, which considered products approved for use on sheep, cattle, pigs, goats and horses based on new information and contained further component assessment reports for toxicology, occupational health and safety and residues.

The APVMA has been considering additional information submitted for the review of diazinon. In doing so, we have been consolidating and updating, where necessary, assessments undertaken since the review commenced.

The APVMA released the toxicology (hazard) component of the diazinon consolidated human health risk assessment in 2011. This component report is a consolidation of toxicological hazard assessments undertaken since the review of diazinon commenced.

In 2000, the APVMA released the diazinon draft report, which identified concerns over the potential risks to workers from some use patterns and a lack of sufficient data to support some use patterns and agricultural practices. Because of these data gaps, we asked registrants and key user groups to provide more data to support the use of this chemical.

In 2002, the APVMA released the revised diazinon draft report after receiving additional information and comments after the publication of the initial draft report. We determined that emulsifiable concentrate (EC) products without stabiliser posed an undue hazard to the safety of people and animals as these products could break down to product highly toxic impurities. We also determined that stabilised EC products used on companion animals posed an undue hazard to the environment. The 2002 report was published along with component assessment reports for residues, chemistry, agriculture, toxicology, occupational health and safety and the environment.

In June 2006, the APVMA released the Diazinon preliminary findings review report, volume 2. Based on new information, we extended the review of diazinon to consider products approved for use on sheep, cattle, pigs, goats and horses. The preliminary findings of volume 2 are supplementary to earlier findings. We concluded that the risks associated with several uses and application methods for diazinon posed an unacceptable risk to human health, trade and the environment.

The APVMA’s key preliminary findings for part 2 were that:

• EC products containing diazinon may form toxic breakdown products following prolonged storage or if diluted in oil or kerosene
• uses of diazinon in enclosed spaces, for domestic pest control and on turf may pose an unacceptable risk of inhalation toxicity from volatilisation during and after application
• all methods of application on sheep (portable and fixed plunge dipping, shower dipping and hand and auto race jetting) pose an unacceptable hazard for workers even when they are wearing personal protective equipment
• the use of diazinon in flea shampoos for dogs may pose a risk to the environment
• the use of diazinon on citrus, pastures, rice, sugarcane and stagnant water or ponds may pose a risk to the environment
• maximum residue limits (MRLs) and appropriate withholding periods can be established for agricultural use only on mushrooms, onions, pineapples and bananas
• diazinon residues in processed dairy commodities containing high fat levels (such as cheese) may pose a risk to Australia’s export trade.

In the preliminary report, the APVMA proposed that:

• EC products containing diazinon should have a shelf life of no longer than 12 months
• the label instructions for diluting EC products in oil or kerosene be removed
• all uses of diazinon in enclosed spaces (except mushroom housing) or for use in domestic pest control and turf treatments be cancelled
• the uses of products containing diazinon as dog shampoos be cancelled
• use on citrus, pastures, rice, sugar cane and stagnant water or ponds be cancelled
• MRLs be established for mushrooms, onions, pineapples and bananas and that all other agricultural uses be deleted from product labels, on the basis of inadequate residue data
• the safety directions on cattle ear tags be strengthened to prevent the use of these products on dairy cows producing milk for human consumption.

Public consultations have been conducted following the publication of the diazinon draft report in 2000, the publication of the diazinon revised draft report in 2002, and the publication of the preliminary review findings, volume 2, in 2006.