Seven institutes from five countries, Austria, England, France, Germany and the Netherlands have collaborated in a study on the influences of solvent and drying method on the toxic limits of wood preservatives against Basidiomycetes tested according to the agar-block method. Two preservatives, a 25% pentachlorophenol-concentrate and tributyltinoxide were applied to pine sapwood and beech and tested against Coniophora puteana. The preservatives were diluted with either acetone. benzene, chloroform or xylene. Slow drying in vapour of the solvent was used for all solvents. In addition quick drying was used for benzene and chloroform and freeze drying for benzene. The results were not conclusive regarding any influence of the solvent and drying method on the toxic limit. There was a trend that the toxic limit of the pentachlorophenol concentrate is decreased by the use of acetone as solvent. An influence of acetone on the toxic limit of tributyltinoxide could not be stated. The results regarding an influence of the drying method on the toxic limit of the preservatives were variable. There is some evidence that the toxic limits are lowered by freeze drying. As this effect is not present in all cases, the differences in the established toxic limits are probably due to normal variation in results and not associated with the drying method.

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