The H2F hazard class in Australia was developed to treat internal framing timber with a surface application of an insecticide, to control mainly termites. Two of the actives approved in AS 1604.1-2010 (and subsequent revisions) for this hazard class are bifenthrin and imidacloprid. The penetration zone of both actives is 0 – 2 mm from the wood surface. Radiata pine sapwood framing timber was treated with bifenthrin or imidacloprid according to Australian Pesticides and Veterinary Medicines Authority approved labels. Samples of the treated wood were analysed over a 12-year period to determine the active retention in the penetration zone. It was found that after 12 years, loss of bifenthrin in the penetration zone was significant. Imidacloprid proved to be more stable with little, if any, loss of the active ingredient in the penetration zone.

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