Temephos Chemical Review

Temephos was nominated for review in 1995 as part of the Existing Chemicals Review Program, which was established to systematically review a number of agvet chemicals that had been on the Australian market for some time. Temephos was nominated because of concerns about occupational health and safety and its potential risk to the environment.

The review of temephos was limited to the single product approved at the time for use on sheep. The product, Coopers Assassin Sheep Dip, was approved for use for the control of body lice (including synthetic pyrethroid resistant strains) on wet or dry short wool sheep by plunge or shower dipping and for the treatment of body lice on long wool sheep by hand jetting. The review of temephos was separate from, but related to, the reviews of diazinon (another organophosphorus compound) and selected sheep ectoparasiticides. While these reviews have been conducted separately, the outcomes of any review may be taken into consideration when conducting related reviews, as they may have an impact on those assessments.

The APVMA began a review of temephos based on the findings and recommendations of the NRA Expert Panel on Organophosphate Sheep Dips, which reported in 2000. The panel reviewed the findings in the United Kingdom Institute of Occupational Medicine’s 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 found that work practices and exposure risks differed between Australia and the United Kingdom, but it could not completely rule out a link between organophosphorus exposure and long-term effects. The panel recommended reducing worker exposure to organophosphorus compounds and that the APVMA review the uses of such compounds on sheep.

The APVMA completed component evaluation reports on temephos in consultation with the Office of Chemical Safety within the Department of Health and Ageing, and the Department of the Environment, and provided the reports to the registrant for comment. However, we made no decision in relation to the component reports at that time. Instead, comment was sought from the affected registrant before the development of a review findings report.

The occupational health and safety (OHS) assessment for the review of temephos was undertaken by the Office of Chemical Safety, which considered all the OHS data and information submitted for the review. The OHS assessment concluded that the APVMA can be satisfied that the continued use of temephos products in portable plunge dipping, fixed plunge dipping or shower dipping would not be likely to be an undue hazard to the safety of workers, provided that they wear appropriate personal protective equipment (PPE) as indicated in the safety directions. However, the office was unable to conclude that the application method of hand jetting was not likely to lead to an unacceptable risk of exposure, even when PPE is worn.

The environmental assessment for the review of temephos was undertaken by the Department of Environment and Heritage, which considered all the environmental data and information submitted for the original registration of the product and additional data submitted for the review.

The environmental assessment raised concerns about the toxicity of temephos to aquatic invertebrates in waters close to the ocean outfall from wool scour sources. The department was unable to conclude that continued use of the product on long wool sheep according to current label directions, even allowing for a three-month wool withholding period, would not be likely to have an unintended effect that is harmful to animals, plants or things or to the environment. It recommended that approved labels be varied to delete all instructions relevant to the treatment of long wool sheep.

The department also considered the issue of soil contamination from temephos dripping off treated sheep. Run-off from treatment areas should not be allowed to contaminate waterways. The department recommended that additional label statements be included on the current label to minimise the hazard posed to wildlife, fish, crustacea and the environment from used or spent dip solution, or from drippings from treated sheep onto soil.

In January 2008, the APVMA approved amended label instructions, which were voluntarily requested by the registrant. The amendments addressed the concerns identified in the OHS and environmental review reports.

Because the concerns that were the basis for the review of temephos had been addressed by the amended label instructions, the APVMA concluded that there was no need to continue the temephos review. Any variation to the current label instructions for temephos, such as an extension of use to long wool, would need to be considered in the context of the concerns identified by the APVMA in the temephos review, particularly the occupational health and safety concerns.