Rain wash-off and leaching of antisapstain fungicides from wood may cause pollution of waterways and may also lead to a decrease in the efficacy of a formulation against fungal degrade as chemicals deplete from the timber surface. In the current study, the leachability of chlorothalonil (CTL) and methylene bis thiocyanate (MBT), the active ingredients of a commercial antisapstain formulation, was determined. Freshly sawn radiata pine (Pinus radiata D. Don) sapwood boards (500 x 70 x 12mm3) were dip-treated, assembled with and without fillets into packets, and subjected to artificial rain after 1, 3 and 6 days of post-treatment fixation time. Chemical analysis were performed on the leachate from each packet using HPLC. In addition, wood samples were taken from various locations within each packet to determine surface retention levels of CTL and MBT before and after raining. The study showed that minute amounts of CTL leached after artificial raining, but MBT did not leach. Initial wood surface retention analysis demonstrated higher levels of CTL than MBT prior to raining, although in the working solution the active ingredients were present in similar concentrations. This suggests that CTL has a higher affinity for radiata pine than MBT. Resistance of CTL leaching increased with post-treatment fixation time. Regardless of posttreatment fixation time, similar MBT losses were observed from the wood surface after raining and they were about the same order of magnitude as CTL. The lack of MBT in the leachate is perhaps related to the diffusion of MBT into the interior of the wood. Furthermore, breakdown of MBT is probably or likely in the leachate.

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