| Summary: | In 2008, the Canadian standard for decking installed above ground was revised, and the penetration requirement was eliminated. This decision was based on field test data and fundamental work on mobility of copper in the preservative formulations that dominated the market at the time. Recently the wood protection industry has shown interest in shifting towards carbon-based preservatives. Thus, it is important to test the efficacy of carbon-based preservative formulations as shell-treatments on Canadian wood species. In this study, samples of spruce heartwood were treated with a formulation containing either tebuconazole or didecyldimethylammonium carbonate (DDAC). The treated wood was exposed outdoors for one year and the leachate from these samples was collected. Tebuconazole and DDAC were detected in the leachate collected, and this indicates that these active ingredients were mobile in the wood after treatment. DDAC was detected in very low concentrations on wood surfaces that were untreated before exposure: 0.03 mg DDAC/g of wood and 0.02 mg of DDAC/g wood were measured for the high and low retentions respectively. The concentration of tebuconazole detected was not different from the control samples. This suggests that mobile DDAC may be able to re-deposit in the wood, but tebuconazole does not re-deposit once it is dislodged from the wood. Furthermore, results showed that spores of Gloeophyllum sepiarium and Oligoporus placentus were able to germinate on untreated check surfaces within 2 weeks on samples collected from exposed, treated wood. This indicates that the re-deposited carbon-based active ingredients were not able to protect the untreated check surfaces against germination of basidiospores of some common fungi isolated from above-ground decking in Canada.
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