Toxicological Effects Of Combined Pollution And Repeated Exposure Of Decabromodiphenyl Ether And Lead In A Earthworm-soil System

Waste electrical and electronic equipment (e-waste) is now the fastest growing waste stream in the world. It was reported that polybrominated diphenyl ethers (PBDEs) and heavy metals (HMs) were main contaminants at e-waste recycling sites (EWRSs) and their potential toxicological effects on terrestrial organisms have received extensive attention. However, few reports pay attention to toxic effects in earthworms with respect to the responses to joint exposure of BDE209 and Pb. In this study, we adopted repeated treatment as exposure model, which is optimized to fit the real environment contamination, to research the combined effects of BDE209 and Pb on earthworm(Eisenia fetida) under laboratory conditions. The results are as follows:(1) Filter paper test on acute toxicity revealed that 48-h LC50 of BDE209 and Pb were 1329.46 and 21.59 μg cm-2, while natural soil test revealed that 14-d LC50 of BDE209 and Pb: were 9963.51 and 1732.74 mg kg-1 respectively. Compared to BDE209, Pb had a higher toxic effect on earthworms. Results of sub-acute toxicity demonstrated that the inhibition of Pb on growth and reproduction of earthworms followed a dose/time-dependent pattern. The avoidance response of earthworms was determined by the value of net avoidance response (NR); earthworms exposed to 100 mg kg-1 of BDE209 displayed avoidance responses, while the soil indicated a more obvious decline of habitat function with the increase of Pb level.(2) Results demonstrated that superoxide dismutase (SOD), catalase (CAT) activity and MDA content were mostly induced. SOD activities declined with increasing chemicals concentration, following certain dose-response relationship. CAT was inhibited during the initial exposure period; while on day 7, it generally recovered and was higher than the control. Additionally, with increasing contaminants level, a dose-dependent relationship could be observed. Compared to the controls, repeated BDE209-Pb exposure significantly facilitated MDA synthesis in all the treatments, however, after 28 d of exposure, MDA levels remained stable and all the treated groups barely displayed obvious difference. Generally, a significant up-regulation of gene expression level appeared after the two chemicals co-exposure; additionally, the responses reflected a dose-effect relationship at a certain extent, especially for Hsp70 gene expression. The relationships of SOD, CAT activities and MDA level with target genes relative transcriptional levels indicated a good positive correlation.(3) The elimination of BDE209 was a multi-step process in earthworm-soil system.BDE208, BDE206, BDE153, BDE99, BDE47 and BDE28 could be detected in the earthworm after exposure. In addition, lower bromination productions would gradually accumulated along with extension of incubation. Generally, the post-clitellum contents of pullutions were higher than that of the pre-clitellum in earthworms. Also, a step exposure model enhanced BDE209 and Pb accumulation in earthworms compared to the repeated exposure, which demonstrated that pollutants through single exposure in earthworms yield higher damage in earthworms than repeated exposure.