Capacity of earthworm and land snail to reveal bioavailability of PCB and PCDD/F in contaminated soil
Résumé
Given their stability, lipophilicity and high persistence, PCB and PCDD/F represent a group of anthropogenic substances that can easily accumulate into the food web. While the transfer and accumulation of these substances are well documented for the aquatic food web, only few studies focused on their transfer from soil to terrestrial organisms. The two projects TROPHé (INERIS) and TROPE (University of Bourgogne Franche-Comté) were undertaken to assess the PCB and PCDD/F transfer into terrestrial biota in order to further evaluate risks to terrestrial ecosystems. Thirty-five compounds were monitoring (6 indicator PCB, 12 dioxin-like PCB, 7 dioxins and 10 furans) from four soils contaminated by a former industrial fire and showing a wide range of concentrations (up to 246 ng I-TEQ.kg-1 for Ʃ17 PCDD/F+12 PCB-DL and up to 35 000 ng.kg-1 for indicator PCB). The transfer of these compounds was then studied in two soft-bodies soil-dwelling invertebrate species: the oligochaete (Eisenia fetida) and the gastropod (Cantareus aspersus). Oligochaetes are one of the most important biotic components in the soil and frequently represent the most abundant species in terms of biomass. They are exposed to soil contaminants by digestive and cutaneous routes. Snails are characteristics of the soil surface and exposed directly to soil contaminants by the same routes as earthworms and also indirectly by ingestion of plants. Their ability to accumulate PCB, PCDD/F is unknown. Worms and snails were exposed in controlled conditions to the soils up to 28 days. The concentrations of the 35 substances were measured after 14 and 28 days of exposure in worms and after 28 days in snails. Bioaccumulation factors (BAF) were calculated according to the concentrations recorded in each soil. The results clearly showed that PCB and PCDD/F were transferred into the worms and snails. A steady state was reach from 14 days of exposure of worms. For both organisms, PCB showed a higher transfer by comparison with PCDD/F as evident by higher concentrations and thus higher BAF (by factor 10) calculated. PCDF (especially 2,3,7,8 TCDF and 1,2,3,4,6,7,8,HpPCDF) were more accumulated than PCDD (OCDD was the most accumulated). Concerning, the PCDD/F the lower BAFworms were observed for the higher chlorinated compound. Such tendency was however not observed for PCB. Among iPCB, PCB153-138-101-180 reached the highest concentrations. Overall, similar tendencies were observed for both species but with higher BAF in worms. This could be the result of a specific ability of accumulation and/or of the way of exposure of these soil invertebrates to contaminants.