Acute toxicity and aqueous solubility of some condensed thiophenes and their microbial metabolites

Petroleum or creosote contamination of surface waters, soils, or groundwaters introduces countless aromatic compounds to these environments. Among these are condensed thiophenes that were shown to be oxidized to sulfoxides, sulfones, and 2,3-diones by microbial cultures. In this study, the acute toxicities of 12 compounds (benzothiophene, benzothiophene sulfone, ben-zothiophene-2,3-dione, 3-, and 5-methylbenzothiophenes, 3-, and 5-methylbenzothiophene sulfones, 5-, and 7-methylbenzothio-phene-2,3-diones, dibenzothiophene, dibenzothiophene sulfoxide, and dibenzothiophene sulfone) were determined by the Microtox® and Daphnia magna bioassays. To aid in determining the toxicities, the solubilities of many of these compounds were determined, which showed that the oxidized compounds were much more water soluble than the parent thiophenes. In nearly every case, the oxidized compounds were less toxic than their parent thiophenes. The Microtox method was more sensitive than the D. magna bioassay, but in general, there was a good correlation between toxicities measured by the two tests. Samples were removed from batch cultures of a Pseudomonas strain capable of oxidizing the thiophenes, and these samples were subjected to Microtox bioassays. These experiments showed that the toxicities of the culture supernatants decreased with incubation time.