Toxicological evaluation of paper mill sewage sediment treated by indigenous dibenzofuran-degrading Pseudomonas sp.

Organic pollutants present in the pulp and paper mill sewage were extracted with dichloromethane/acetone (1:1 v/v), and the extract was added to minimal salt medium to study the degrading and detoxifying potential of Pseudomonas sp. strain ISTDF1. GC-MS analysis performed after biodegradation showed removal of chlorinated compounds like dichloroacetic acid, heptadecyl ester (RT = 28.99) and formation of simpler compounds like 4-isopropylbenzaldehyde (RT = 7.52). Methyltetrazolium (MTT) assay for cytotoxicity, 7-ethoxyresorufin-O-deethylase (EROD) assay for dioxin-like behaviour and alkaline comet assay for genotoxicity were carried out in human hepato-carcinoma cell line HuH7 before and after bacterial treatment. The bacterium reduced toxicity as shown by a 5-fold increase in LC50 value, 2110-fold reduction in benzo (alpha) pyrene equivalent value and an 8-fold reduction in Olive Tail Moment after 240 h treatment. The EROD assay was found to be a useful method which indicated positive correlation with MTT and comet assay in post-biodegradation toxicity evaluation. (C) 2012 Elsevier Ltd. All rights reserved.