Methamidophos Chemical Review

In April 2002, the APVMA began a review of methamidophos because of concerns about its high acute and chronic toxicity and its potential to cause delayed neurotoxicity. This action was based on advice from the Therapeutic Goods Administration that methamidophos may pose a potential hazard to public health and should be re-evaluated using contemporary data and assessment standards.

Methamidophos has also been listed as a chemical subject to the Rotterdam Convention on the Prior Informed Consent Procedure for Certain Hazardous Chemicals and Pesticides in International Trade (the Rotterdam Convention). Australia became a party to the convention on 18 August 2004.

Prior informed consent promotes a shared responsibility between exporting and importing countries in protecting human health and the environment from the potentially harmful effects of certain hazardous chemicals that are being traded internationally. It allows countries to make informed decisions about the chemicals they import and contributes to the management of chemical risk.

Methamidophos is included in the prior informed consent procedure (in soluble liquid formulations that exceed 600 grams of active ingredient) because of its acute hazard classification and concerns about its impact on human health under conditions of use in developing countries.

In May 2002, the APVMA released the Methamidophos review scope document, which outlined the information needed to conduct a scientific assessment of methamidophos.

Voluntary cancellation by holder. Review no longer necessary.

On 15 June 2012, all approvals of the active constituent, methamidophos, were cancelled at the request of the approval holder. In addition, registrants have voluntarily cancelled all products containing methamidophos.

A two-year phase-out period, ending on 15 June 2014, applies to the supply and use of existing stocks of methamidophos products.

With the cancellation of all methamidophos active constituent approvals and products containing methamidophos, the continuation of the review of methamidophos is no longer necessary.

In June 2012, the APVMA released the Human health risk assessment of methamidophos for information purposes only, as all approvals of the active constituent were concurrently cancelled at the request of the approval holder. The assessment concluded that there was not sufficient evidence of delayed neuropathy to prevent the ongoing registration of methamidophos. In addition, the Office of Chemical Safety revised the acceptable daily intake for methamidophos and established a new acute reference dose.

However, while the toxicological assessment supported the ongoing use of methamidophos products, further assessment would be required for any future application for registration due to concerns about possible human health impacts under conditions of use. This would ensure that appropriate maximum residue limits (MRLs) are established and that dietary exposures to methamidophos residues are acceptable.