Persistence of Chloropicrin in Western Redcedar Poles

Five years after treatment with cloropicrin (trichloronitromethane), western redcedar sections maintained in a controlled environment were examined by open-tube and closed-tube bioassay methods in order to determine the long-term effectiveness of fumigant treatment. The results of these tests, which closely paralleled those run 2 years after treatment, indicated that the chloropicrin moved through and remained in the cedar heartwood at fungitoxic levels. Cores removed from locations adjacent to those used for the closed-tube bioassays were divided into segments and extracted in hexane for analysis by a gas chromatograph equipped with an electron capture detector. Chloropicrin concentrations generally increased from the wood surface inward and ranged from 1.3 to 53,047.8 pg/cm3 of wood. The poor correlation between chloropicrin concentration and growth of the test fungus in the closed-tube bioassay suggests that the toxicity of volatile heartwood constituents may have affected the results of the bioassay. The results show that although most of the fumigant remained in the wood interior, sufficient levels migrated to the wood surface to suggest that chloropicrin treatment may protect poles from sapwood in addition to heartwood decay. Thus fumigant treating appears to be viable for prolonging the service life of western redcedar poles.

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