Effect of chlorination on toxicity of wastewater effluents from different treatment systems to HepG2 human hepatoma cells

Effect of chlorination on the toxicity of wastewater effluents treated by activated sludge (AS) and submerged membrane bioreactor (S-MBRB) systems to HepG2 human hepatoblastoma cells was investigated. In addition to cytotoxicity assay, the DNA microarray-based transcriptome analysis was performed to evaluate the change in modes of toxic actions (MOAs) of effluents by chlorination. Effluent organic matters (EfOM) and disinfection by-products (DBPs) were characterized by using Fourier transform mass spectrometry (FT-MS). The cytotoxicity of AS effluent was elevated by chlorination, while the toxicity of S-MBRB effluent was reduced. The averaged O/C ratio of EfOM in S-MBRB effluent was lower than that in AS effluent. The results of the transcriptome and FT-MS analyses suggested that lower O/C molecules influenced on “response to hormone stimulus” and “acute inflammatory response” but those were decreased by chlorination, which consequently reduced cytotoxicity. On the other hand, larger number of DBPs and other molecules were increased in AS effluents by chlorination. Those molecules might influence on “cellular metabolic process”, which consequently elevated cytotoxicity. Therefore, the combination of the toxicity assays and chemical analysis demonstrated the changes in severity of cytotoxicity and MOAs by chlorination, and the difference of chemical characteristics which relate to those toxicity changes. We examined the gene expression alteration in human hepatoma cell line, HepG2 exposed to the chlorinated wastewater effluents from membrane bioreactor and the activated sludge process. Human Genome Focus Array, which represents 8,795 verified human sequences, was used. All effluent samples were concentrated by using solid phase extraction (SPE). SPE fraction from MQ water was used as controll. For duplicate, two dishes were prepared for each sample and individually treated in parallel.