BIOASSAYS FOR BENOMYL ADSORPTION AND PERSISTENCE IN SOIL

Two bioassay methods were modified to evaluate persistence, adsorption and biological availability of the fungicide benomyl in soil. The amount of biologically-available fungicide was assayed using the fungus Penicillium expansum Link ex Gray. The bioassay results were not significantly different from those obtained by spectrophotometry. The bioassays detected methyl 2-benzimidazole carbamate (MBC), which is the major toxic degradation compound of benomyl, to a limit of detection of 0.2 mug g-1 and a limit of quantitation of 0.5 mug g-1 in soil and leachate. The bioassays could be completed within 2 days. The amount of MBC adsorbed by soil varied, depending on soil type and fungicide concentration. In vitro soil degradation studies showed a half-life for MBC of around 4 weeks.