Decomposition of Basamid in Douglas-fir heartwood Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/hh63sz88g

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  • Basamid^R (3,5-dimethy1-1,3,5,2H-tetrahydrothiadiazine- 2-thione) is a crystalline powder used as a soil sterilant. This fumigant acts in soil by decomposing to methylisothiocyanate (MITC), the primary active ingredient, as well as hydrogen sulfide, methylamine, and formaldehyde. In wood, Basamid decomposes too slowly to be efficacious against decay fungi unless amended with various catalysts. Environmental conditions also play a role in Basamid decomposition rates. This study explored the use of selected additives to enhance Basamid decomposition. No Basamid decomposition was observed in Douglas-fir heartwood incubated at 12% MC or 5°C. The rate of Basamid decomposition increased with wood MC from 12 to 60 % and temperature from 5°C to 23°C. A pH 12 buffer powder increased decomposition; however, the primary breakdown product was carbon disulfide, a chemical which is fungitoxic but has no interaction with wood and, thus, no residual effect. Copper sulfate had a tremendous catalytic effect on Basamid and favored the production of MITC over other compounds. The effect of copper sulfate was more pronounced soon after treatment, providing an initial burst of MITC release and then a steady, moderate rate of release. Manganese and magnesium, as well as wood alone, provided no catalysis in laboratory studies. No volatile decomposition products besides MITC and carbon disulfide were detected. Field tests indicated that copper sulfate plus the pH 12 buffer were effective in catalyzing MITC production and providing a more evenly distributed protective chemical loading than was metham sodium (also known as Vapam), the most widely used wood fumigant. While MITC levels produced from metham sodium decreased substantially within 1 year, MITC release was constant at moderate rates for at least 3 years from Basamid amended with copper sulfate and the pH 12 buffer. These tests indicate that Basamid, when amended with an appropriate additive, will release MITC at controllable levels that should provide protection against internal decay in utility poles. This solid chemical provides a safer and possibly longer lasting remedial treatment than the currently used conventional wood fumigants.
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