Microbial toxicity in soil medium.

A laboratory procedure using the respirometer was developed to measure microbial toxicity in soils of organic chemicals. The procedure was tested with Polytox, a commercial microbial test culture, on 35 organic chemicals. The test protocol was reproducible with a mean standard deviation of 0.08 mg chemical/g of soil for eight chemicals. The assays were also carried out at different moisture-holding capacities of soil. Correlation between toxicity tests done in aqueous medium and soil for Polytox test culture was statistically significant and yielded an r2 of 0.816. Details of the laboratory procedure and test results are presented together with comparisons of toxicity of chemicals in the soil medium with that in aqueous medium for the same test organism. A few practical applications are discussed.