Studying the genotoxic effects induced by two kinds of bentonite particles on human B lymphoblast cells in vitro

The aim of the present study was to evaluate the genotoxic effects induced by native and active bentonite particles (BPs) on human B lymphoblast cells using comet assay and cytokinesis-block micronucleus (CBMN) assay in vitro. The cells were exposed to BPs at the concentrations of 30, 60, 120 and 240 μg/ml for 24, 48 and 72 h, respectively. The quartz contents of native and active BPs were 6.80 ± 0.20 and 6.50 ± 0.10%, respectively. Gypsum and DQ-12 quartz served as negative and positive controls. The results of comet assay showed that DNA damage induced by native and active BPs was significantly higher than that induced by gypsum control (P < 0.05 or <0.01), and increased with exposure concentration and duration. When the cells were exposed to BPs at the doses of 120 and 240 μg/ml for 72 h, DNA damage induced by active BPs and native BPs was significantly higher than that induced by DQ-12 quartz (P < 0.01), and DNA damage induced by active BPs enhanced significantly, as compared with native BPs (P < 0.01). The results of CBMN assay demonstrated that both native BPs and active BPs could induce significant micronuclei, as compared with gypsum control (P < 0.05 or <0.01). However, there was no significant difference of micronucleus frequency (MNF) among native BPs, active BPs and DQ-12 quartz. The water-soluble fractions from two kinds of BPs did not induce significant DNA damage and micronuclei. These findings indicated that the genotoxicity induced by active BPs and native BPs could be detected in comet assay and CBMN assay in vitro, the insoluble particle fractions from BPs may play a main role in the genotoxic effects induced by BPs.