Metham sodium, dazomet and methylisothiocyanate Chemical Review

In September 1995, the APVMA (then the NRA) began a review of metham sodium and dazomet because of occupational and public exposure concerns. The nomination for special review followed advice from the Therapeutic Goods Administration of adverse occupational health and safety effects linked to the use of metham sodium.

Dazomet was included in the review because it has similarities to metham sodium as a precursor to generating MITC. Both metham sodium and dazomet rapidly decompose in soil to MITC. The decomposition is a chemical rather than a biological process and forms the basis of their pesticidal mode of action.

In November 1995, the then Australian Government Department of Health and Human Services requested that the review be extended to include MITC. The use of metham sodium and dazomet leads to MITC residues, so the toxicity of MITC is important in the assessment of the potential risks of metham sodium and dazomet use.

In June 1997, the APVMA released the Metham sodium, dazomet and MITC special review report. The APVMA concluded that metham sodium product labels required revision to provide additional warnings and to remove methods of application with a potential for unacceptable levels of occupational exposure.

In the final report, the APVMA recommended:

• strengthening the restraints on existing uses of metham sodium: it must not be applied in high wind, temperatures over 32 degrees celsius, dry soil, or conditions of low humidity
• discontinuing some uses of metham sodium: it must not be used by hand or by directed spraying (including sprinkler can), in overhead sprinkler systems, in treating potting soil by the loose mixed method or via shredder, or by flood irrigation
• strengthening safety directions and information on metham sodium and dazomet product labels for personal protective equipment, re-entry or re-handling periods and minimisation of vapour escape in treated soil
• revising product labels to include statements specifically prohibiting the discontinued methods of application to ensure that they are not allowed under any state control of use regimes
• requiring the submission of material safety data sheets for all products for assessment as a condition of registration
• implementing an evaluation period from 1 January 1998 to 30 June 1998 to assess the operational effectiveness of the revised conditions of registration (following this evaluation, metham sodium and dazomet may be declared restricted chemical products if that is deemed necessary).

The APVMA has recommended that these compounds be declared restricted chemical products. Metham sodium and dazomet are listed for determination as restricted chemical products with the state and territory governments.