Bioassay of various pesticides by microcalorimetry measuring the metabolic heat of yeast.

Using a microcalorimeter, the heat evolved during incubation of yeast cultures at 30 degrees C was detected in the form of a growth thermogram (metabolic heat-incubation time curve). The correlation between the growth thermograms and the growth curves obtained by colony counting or from the turbidity measurements of the cultures was very good. In this study, the effects of 12 pesticides that are used widely on golf courses on the growth thermograms of yeast were investigated and the inhibitory action of the pesticides on the growth of yeast was quantitatively evaluated using a microcalorimeter (Biothermo Analyzer). The growth thermograms were applied to estimate the microbial activity of yeast in the presence of pesticide and to determine the 50% inhibitory concentration (K) and minimum inhibitory concentration (MIC), which can be regarded as good indexes of the toxic potency of pesticides. It was found that the addition of TPN, captan, thiuram and copper oxide to the yeast cultures clearly induced inhibitory action on the growth of yeast cells. On the other hand, the other 8 pesticides, iprodione, isoprothiorane, chloroneb, pencycuron, metalaxyl, toleclofos-methyl, flutolanil, and mepronil did not affect the growth over the concentration range up to 30 mg/l.