The long-term decay resistance of refractory wood shell-treated with chromated copper arsenate (CCA) in above-ground exposures has been attributed to mobile copper that migrates into checks and inhibits the germination of basidiospores. Copper from micronized copper quat (MCQ) has also been shown to migrate into checks suggesting similar performance as a shell treatment, but questions have been raised about the form of this mobile copper. The concern was that if the copper is present as small particles rather than ions, it might not provide protection against basidiospore germination. The present work examined checks on MCQ-treated boards exposed above-ground in Vancouver for one year using Environmental Scanning Electron Microscopy (ESEM) with energy dispersive X-ray spectroscopic mapping. The copper detected on checks from MCQ-treated wood was not present as micro- or macro-particles. ESEM and EDS data were consistent with the vast majority of detected copper being soluble copper adsorbed to the wood, but did not preclude the presence of some copper-containing nano-particles below 9 nm. In addition, a laboratory test evaluated the efficacy of leachates from treated wood on spore germination. Untreated spruce disks were attached to wood treated with ACQ, MCQ or CCA for up to 36 days under conditions of periodic water spray and high humidity. These disks were used for either copper analysis or spore germination testing against Gleophyllum sepiarium and Oligoporus placentus. After eight weeks of incubation, spores had germinated on most of the untreated controls and on most of the disks previously attached to ACQ-treated wood. Disks previously stored adjacent to MCQ- and CCA-treated wood were largely free of spore germination. These data suggest that the mobile copper from MCQ is effective against basidiospore germination, and that the mobile copper from ACQ may be less effective under the test conditions in this study.

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