Estimating the toxicity of chlorinated organic compounds using A multiparameter bacterial bioassay

A battery of microbial tests that included contemporary measurement of specific growth rate, intracellular ATP level, and respiration rate proved capable of distinguishing among toxicants that acted primarily as (a) catabolic inhibitors, (b) uncouplers, and (c) inhibitors of biosynthetic processes. The concentration of chlorinated phenols and ethanes that produced a 50% reduction in specific growth rate (ECk₅₀) provided the most useful single‐parameter indication of relative chemical toxicity generated within the test battery. Among the chlorinated ethanes tested, toxicity resulted from nonspecific chemical interactions with bacterial membranes, as indicated by correlation between toxicity (ECk₅₀) and measures of lipophilicity. The ECk₅₀ value for 1,2‐dichloroethane was 8.5 × 10⁻³M as compared to 1.7 × 10⁻⁴M for the more hydrophobic pentachloroethane. Intermediate ECk₅₀ values were obtained for 1,1,1‐trichloroethane and 1,1,2,2‐tetrachloroethane. For a comparable degree of lipophilicity, the chlorinated phenols were about an order of magnitude more toxic than chlorinated ethanes. ECk₅₀ values for Spirochaeta aurantia at pH 7 ranged from 1.3 × 10⁻³M for 2‐chlorophenol to 9.4 × 10⁻⁶M for penta‐chlorophenol. There was indirect evidence that the toxicity of chlorinated phenols arises from both specific and nonspecific chemical interactions with bacterial membranes. The test battery proved capable of distinguishing among the relative toxicities of the chemicals tested at least as well as other bioassay procedures including Microtox and Daphnia‐based tests. However, ECk₅₀ was less sensitive than parametric measures of chemical toxicity generated via other procedures.