Toxicity of Increased Amounts of Chemicals and the Dose–Response Curves for Heterogeneous Microbial Populations in Soil

The paper deals with the interpretation and classification of dose–response curves in order to understand the way in which the heterogeneous soil microbial population behaves under chemical stress. The evaluation is based on a set of about 500 toxicity tests, in which geometrically increasing doses of toxicants were applied to soil samples. The responses of the microflora were measured by various methods, e.g., Fe(III) reduction, substrate induced respiration, arginine ammonification, and several enzyme activities. The data reveal that microbial populations in soil react more complexly than homogeneous groups of test subjects which are common in classical toxicology. The diverse types of dose–response curves are attributed to a varying sensitivity of different parts of the soil microflora and influences of the habitat soil. A proposal for the interpretation and classification of microbial dose–response curves is presented. Four basic types of dose–dependent effects and several combined sequences of them can describe the reaction patterns found up to now. Since experiments with heterogeneous populations are lacking in classical toxicology, the results can be used as a key for further research regarding the toxicity of chemicals against plant, animal, and human populations.