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 (α) 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.