ESTIMATING TOXICITY OF ORGANIC-CHEMICALS TO ACTIVATED-SLUDGE MICROORGANISMS

Inhibition of respiration rates (IC50) of activated-sludge (AS) microorganisms and a commercial surrogate culture, Polytox, were measured using the respirometric technique for 50 organic chemicals. The correlation between the IC50 values for the two cultures was found to be highly significant with r(2) = 0.928, the Polytox cultures being more sensitive than AS cultures. Using AS experimental inhibition data for a training set of 40 chemicals, a single-variable quantitative structure activity relationship (QSAR) model was developed to estimate IC50 for AS. When this QSAR model was tested on a testing set of 10 ''new'' chemicals, the predicted IC50 values agreed well with the experimentally measured values, with r(2) = 0.834 at p = 0.0002. Inhibition data reported in the literature for 32 additional chemicals were also compared with predictions made by the QSAR model, and the agreement was satisfactory, with an overall r(2) of 0.798, at p = 0.0001.