Investigation On The Influence Of Decabromodiphenyl Ether On Lead Bioaccumulation And Toxicity In The Earthworm-Soil System

Polybrominated diphenyl ethers (PBDEs) and heavy metals are the main contaminants at e-waste recycling sites, and their potential toxicological effects on terrestrial organisms have received extensive attention. Among these contaminants decabromodiphenyl ether (BDE209) and lead (Pb) are widespread. In this study, the combined effects of BDE209 and Pb on earthworm (Eisenia fetida) using natural soil method were studied under laboratory conditions. The results are as follows:(1) The inoculation of earthworms in the BDE209 contaminated soils could facilitate the removal effectiveness of BDE209. BDE209 uptake flux constant (a) increased with increasing BDE209 exposure concentrations, while uptake rate constant (ku) and bioaccumulation factor (BAF) exhibited almost contrary response trends. Earthworms showed fast depuration of BDE209 with half lives about 3 days. Total BDE209 concentrations in earthworm, wormcast and soil samples followed the sequence of soil> wormcast earthworm, while the total BDE209 metabolism concentrations (BDE208, BDE207, BDE206, BDE153, BDE99, BDE47 and BDE28) followed the sequence of earthworm> wormcast (soil). The BDE209 in earthworm, soils and wormcast were mainly debrominated to nona-bromobiphenyl ethers (BDE208, BDE207 and BDE206). In Comparison with the single Pb exposure, the addition of 100 mg kg-1 BDE209 obviously increased the soil pore water Pb concentration and damaged the earthworms body wall structure. These might lead to increase the Pb uptake flux constant and equilibrium concentration. When the earthworms were exposed to Pb spiked soils also containing BDE209 at the levels of 10 and 100 mg kg-1, the contents of Pb associated with subcellular fraction E alarmingly declined, while those associated with fractions D and C generally elevated, indicating that the existence of higher levels of BDE209 might affect uptake and subcellular distribution of Pb in earthworms.(2) Superoxide dismutase (SOD) was insensitive to short-term (7 d and 14 d) BDE209 exposure, while it showed induction trend after long-term (21 d and 28 d) exposure (p< 0.05). In general, the catalase (CAT) activity was activated during the entire exposure period, while the peroxidase (POD) and glutathione-s-transferase (GST) activities were inhibited, indicating that CAT played a more important role in eliminating H2O2.1 mg kg-1 BDE209 treatment promoted total antioxidant capacity (T-AOC) throughout the test. When BDE209 concentrations increased to 10 and 100 mg kg-1, the T-AOC declined in almost all exposure groups, indicating that the natural antioxidant defenses were overwhelmed. On the whole, there was a marked enhancement trend of MDA content compared to the controls. This confirmed the results that the reactive oxygen species (ROS) were induced and lipid peroxidation occurred. During the uptake phase, the measured NRRTs generally decreased with increasing BDE209 concentrations and exposure times. The increased NRRTs during the depuration period could be evaluated as the earthworms had gradually recovered from BDE209 exposure. Compared with the single Pb exposure, the addition of 1 mg kg’1 BDE209 barely affected enzymatic activities and T-AOC, while the additions of 10 and 100 mg kg-1 BDE209 depressed enzymatic activities and T-AOC. Pb induced the reduction in the enzymatic activities and T-AOC, in the presence of BDE209, resulting in an increase in ROS which initiated an increase in lipid peroxidative products, both of which would have contributed to the destablization of the lysosomal membranes.(3) The assay with single chemical spiking only caused a induction of earthworm tissue detoxification in terms of SOD, CAT and Hsp90 (Heat shock protein 90) gene expressions in contrast with the controls. This might be an important defense mechanism against oxidative damage. Compared with the single Pb exposure, the addition of 1 mg kg-1 BDE209 barely affected these three gene expressions, while 10 and 100 mg kg-1 BDE209 supply depressed the induction of SOD and CAT gene expressions but facilitated Hsp90 gene expression.