Concerns about indoor air quality due to mold growth have increased dramatically in the United States. In the absence of moisture management, fungicides need to be developed for indoor use to control mold establishment. An ideal fungicide for prevention of indoor mold growth on wood-based materials needs to specifically prevent spore germination and provide long-term protection under conditions of high humidity. Fungicides intended for indoor use must exhibit no mammalian toxicity, be odorless and emit no VOCs. Classes of compounds meeting one or more of these criteria include acids, phenolic compounds (antioxidants), pharmaceuticals, commercial and experimental wood preservatives, food preservatives, and plant essential oils. Wood preservatives and food preservatives were initially screened at various concentrations for inhibitory properties to mold fungi on 2% malt agar (MA). Many compounds that inhibited the test fungi on MA failed to substantially inhibit mold growth on unseasoned southern pine at higher concentrations than the minimal inhibitory concentration determined on MA. Subsequently, compounds were screened on unseasoned southern pine stakes. Pine stakes were dipped for 15 seconds in varying concentrations of the test chemicals according to the ASTM standard test method D4445 for controlling mold on unseasoned lumber. Stakes were challenged with Penicillium chrysogenum PH02, Aspergillus niger 2.242, and Trichoderma viride ATCC 20476 spore preparations. Following a 4-wk incubation, stakes were rated from 0-5 with 5 representing heavy mold growth. An inihibition rating of 0 to 1 is indicative of successful mold inhibition. The best overall average ratings for wood preservatives were seen in stakes treated with 5% Bor-A-plus or Cu+, which were highly inhibitory to all test fungi. High concentrations of ethanolamine (10%) and thujaplicin (10%) were inhibitory to all test fungi. Pine resin (50%) solely inhibited P. chrysogenum. Of the food preservatives tested, five percent sodium benzoate and potassium sorbate inhibited all test fungi, while calcium propionate selectively inhibited A. niger. Pharmaceutical antifungals such as voriconazole (2.5mg/mL), thiabendazole (25mg/mL), and miconazole (20mg/mL) completely inhibited all test fungi on unseasoned pine, while other azole-derivatives failed to inhibit mold growth. Nystatin (10,000 units/mL) inhibited only A. niger. A combination of effective chemicals should be considered as one strategy to provide long-term protection of wood-based building materials from mold establishment.
Clausen, Carol A.; Yang, Vina W. 2003. Mold inhibition on unseasoned southern pine. Thirty-fourth annual meeting of the International Research Group on Wood Preservation : 2003 May 18-23, Brisbane, Queensland, Australia. Stockholm, Sweden : IRG Secretariat, 2003: 9 pages