Detoxification of fluorene, phenanthrene, carbazole, and p-cresol as studied by the Microtox

A column experiment was conducted in order to study the evolution of the toxicity of creosote-related compound mixtures during aerobic biodegradation in a saturated hydrodynamic groundwater environment. The Microtox assay was used to characterize the toxicity of phenanthrene, fluorene, carbazole and p-cresol, separately and in mixtures, and to evaluate their detoxification during biodegradation. Phenanthrene, fluorene and p-cresol, separately solubilized in an aqueous phase, produced toxic effects on P. phosphoreum luminescence emission; 15 min-IC50 values of 140 {micro}g/L, 600 {micro}g/L and 1,500 {micro}g/L respectively were determined. Carbazole appeared as poorly toxic. The detoxification of the mixture solutions was demonstrated after having passed through the columns. Phenanthrene, fluorene and carbazole combined at different proportion produced between 24.4% and 49.3% of inhibition, whereas at the last port of the columns the inhibition values of the outflows averaged 6%. The presence of 10,000 {micro}g/L of p-cresol enhanced this efficiency of detoxification, since the inhibition of the mixture with the other compounds, which was 81.4% before injection, decreased to 15.8% after having passed through the first 5 cm of the column, and was not detectable at its last two pores. The acute toxicity test corroborated the chemical analysis, reflecting the compound elimination.