Interactions Between Sodium N-Methyldithiocarbamate and Douglas-Fir Heartwood
Keywords:Fumigants, Douglas-fir, Vapam<sup>®</sup>, decomposition, preservation
Vapam® (NaMDC) is the fumigant most commonly used to arrest and control decay of utility poles. While volatile fungitoxins are detectable only 1 to 2 years after treatment, poles treated with Vapam® remain free of decay fungi for 6 to 17 years. Vapam® decomposes to produce volatile fungicides as well as a number of nonvolatile products that may provide long-term protection. The degree and rate of decomposition of NaMDC were evaluated by using a gas chromatograph and a high-performance liquid chromatograph to analyze extracts from Vapam® mixtures with wood, cellulose, vanillin, starch and glass.
Compounds similar to those produced from Vapam®-soil mixtures were found in the mixtures tested. Of the materials identified, sulfur was the most abundant nonvolatile product in wood mixtures and may play a role in long-term wood protection. Sulfur was present only at low levels in cellulose mixtures. These results, coupled with the low levels of volatile MIT produced in the cellulose mixtures, suggest that lignin is an important site for Vapam® decomposition reactions. Further studies are suggested to determine the role of nonvolatile decomposition products in arresting decay away from the point of application.
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