Study On Evaluation Methods Of Polychlorinated Biphenyl Bioavailability To Earthworm In Soil

PCBs (Polychlorinated biphenyls, PCBs) are global persistent organic pollutants with carcinogenic, teratogenic, mutagenic and endocrine disrupting effects. Dismantling electric power capacitor or transformer has lead to surrounding soil pollution in China. Safeties of living environment, agricultural product and ecosystem are seriously threated by PCB pollution. Risks of PCBs largely depend on the bioavailability in soil. Total concentration of pollutant can not accurately reflect the bioavailable fraction of pollutants, and overestimates their toxicity and environment risk to organism. Therefore, it is urgent to develop a fast and accurate method to evaluate bioavailability of PCBs in soil. In the present study, in order to to find a suitable and rapid extraction method to predict PCBs bioavailability, we compared four methods evaluating the bioavailability of PCBs in the aged soil and compost amended soil with accumulation of earthworms (Eisenia fetida). The main results are presented as follows:(1) PCBs spiked loam was aged for one year. Four methods mild organic solvent extraction, mildβ-cyclodextrin extraction (HPCD), semi-permeable membrane passive sampling devices (SPMD) and solid-phase micro-extraction (SPME) were used to evaluate the bioavailability of PCBs in soil. The amounts of PCBs extracted by the four methods showed significant linear relationships to those accumulated by earthworm (p<0.05). R~2 of linear regression between four methods and earthworm accumulation were 0.991, 0.984, 0.991 and 0.947 respectively, and value of slope rate k were 1.899, 1.300, 0.1460 and 0.0126 respectively. Amount of PCBs extracted by butanol was much higher than those accumulated by earthworm. Amounts of PCBs extracted by SPMD and SPME were far lower than those accumulated by earthworm. The profiles of PCB congeners in earthworms were quite different from those of above three methods. The ratio of HPCD extraction and earthworm accumulation was near one, and they had similar composition of PCB congeners. Thus, mild HPCD extraction is a good method to predict bioavailability of PCBs to earthworm in soil.(2) Above four methods were applied to predict PCB bioavailability in compost amended soil. In the compost amended soil which was added with surfactant soybean lecithin, inoculated with degraders and earthworm, bioavailability fraction of PCBs in soil predicted by mild HPCD extraction was close to the amount accumulated by earthworm. Fraction of PCBs in soil predicted by mild butanol extraction was much higher than the amount accumulated by earthworm.And using SPMD and SPME methods could not predict the amount of bioavailable PCBs in the soil accurately. Similar results were observed in the compost amended soil which was added only with surfactant soybean lecithin. Thus, we can conclude that mild HPCD extraction is a precise method to predict the amount of bioavailable PCBs to earthworm in soil.