Detoxification of fluorene, phenanthrene, carbazole and p-cresol in columns of aquifer sand as studied by the Microtox (R) assay

The changing in the toxicity of mixtures of creosote-related compounds duri ng their aerobic biodegradation was studied in columns of saturated aquifer material. The Microtox" assay was used to measure the toxicity of phenanth rene, fluorene, carbazole and p-cresol, added individually or in a mixture and to evaluate their detoxification during migration through the columns. When tested alone, phenanthrene, fluorene and p-cresol, inhibited Vibrio fi scheri luminescence emission (15 min IC50=140, 750, 1500 mu g/L respectivel y). In contrast, the toxicity of carbazole was minimal. Phenanthrene, fluor ene and carbazole, added concomitantly at concentrations varying between 30 and 300 mu g/L, produced between 24.4 and 49.3% inhibition. Comparison wit h individual toxicity responses suggested antagonistic interaction between these compounds. The toxicity of the mixture solutions decreased upon passa ge through the columns since the inhibition caused by the effluent solution s averaged 6%. Additionally, p-cresol (10,000 mu g/L) enhanced the efficien cy of detoxification of the column system; the inhibition by the compound m ixture decreased from 81.4% (SD = 2.0) to 15.8% (SD = 1.8) after having pas sed through the first 3.8 cm of the column, and was undetectable at the two other downgradient ports. A comparison of the data of product disappearanc e and changes in toxicity indicated that detoxification was the result of t he disappearance of phenanthrene and p-cresol. However, the persistence of fluorene and/or potential metabolites seemed to have caused some residual t oxicity. (C) 1999 Published by Elsevier Science Ltd. All rights reserved.