Development of threshold values for boron and fluoride in non-soil contact applications

The thresholds of boron and fluoride against selected decay fungi (Postia placenta, Gloeophyllum trabeum, and Trametes versicolor) were determined in Douglas-fir sapwood and heartwood in non-soil contact exposures. Even small amounts of chemical provide exceptional protection to heartwood and limited our ability to provide accurate thresholds. For the brown-rot fungi, thresholds for sapwood were far lower than those previously found and ranged from 0.40 to 0.44 kg/m3 (boric acid equivalent) for boron; the threshold was 0.33 kg/m3 for fluoride (as fluoride). Weight losses for the white-rot fungus, T. versicolor, were too low to allow for threshold determination. The results illustrate the efficacy of boron and fluoride in non-soil-contact exposures.

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