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US Forest Service Research & Development
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Low Toxicity Method for Inhibiting Mold on Wood

Mold on Wood

Development of synergistic biocides to protect wood in interior applications has been of particular interest since the recent increase of indoor mold infestations. Many products have been developed to address the recent influx of indoor mold infestations. Researchers must emphasize the use of environmentally benign chemicals due to the need for safety of human occupants. Some typical strategies employed include one or more of the following: naturally occurring antimicrobial or insecticidal chemicals, synergistic combinations of chemicals, chemicals with known performance (and previous EPA registration). Unfortunately, safely controlling fungal growth in the same environment as human occupants is difficult to accomplish. Since fungi and humans are both eukaryotic, (i.e. higher multi-cellular organisms with organized nuclei), metabolic inhibitors of fungi are likely to be toxic to humans (Clausen and Vina Yang, Ph.D. Forest Products Laboratory 2005a). Use of naturally occurring antimicrobials needs to be approached with caution, since many but not all naturally occurring compounds are toxic in tissue culture. Chemicals with previous EPA approval are limited, but certainly, new, unique combinations of such chemicals can create new formulations with antimicrobial or insecticidal properties (Clausen and Yang 2003). Occasionally, combinations of known fungal or insect inhibitors are synergistic, i.e. combined chemicals are more effective than the individual components at higher concentrations. One such synergistic combination, called Durazol, incorporates some known antimicrobials and insecticides, namely boric acid and propionic acid with a quaternary amine compound and an azole to provide protection against mold fungi, stain fungi, decay fungi, and termites at lower concentrations than any of the individual components alone (Clausen and Yang 2004; 2005b; 2005c; 2007).