Transfer of PCB and PCDD/F from soil to the terrestrial ecosystem with potential risk assessment for Humans and for the ecosystems
Résumé
Persistent organic pollutants (POPs) such as dioxins/furans (PCDD/PCDF) and polychlorinated biphenyls (PCBs) have been widely studied in aquatic ecosystems and in animals intended for human consumption. Their high stability and accumulation into fat led to a number of well-documented incidents (contamination of milk and meat/fish). However, only few studies have focused on their transfer from soil to terrestrial organisms, as these pathways are usually considered as minor. Two research projects (TROPHé and TROPE) were devoted to assess POPs’ transfer toward first links of food webs (vegetables, fodder and soil invertebrates) in order to further assess health human risks and terrestrial ecosystems risks. Based on two main experimental studies conducted in laboratories to evaluate bioconcentration factors, risk assessment was performed using multi-media exposure models: on one hand, Modul’ERS developed by INERIS to assess transfer of contaminants from the environment through the local food chain to human exposure and risk, and on the other hand, TerraSysTM for ecosystems risk, developed by Sanexen. Four contaminated agricultural soils were sampled in the vicinity of a former industrial plant and thirtyfive compounds were analyzed (6 indicator PCB, 12 dioxin-like PCB, 7 dioxins and 10 furans). These soils were selected to present a wide range of concentrations (up to 246 ng I-TEQ.kg-1 for Ʃ17 PCDD/F+12 PCB-DL/up to 35,000 ng.kg-1 for indicator PCB). They were tested under controlled conditions. In a first experiment, POPs were measured in leave-, fruit- and rootvegetables widely grown in French gardens (zucchini, lettuce, potato, carrot, green bean). In the second experiment using the same polluted soils, POPs were measured in soft tissues of two soil invertebrates (earthworms and snails). In addition, bioindicators and soil PCB bioaccessibility through in vitro test (Forhest) were also evaluated. Results showed that POPs were both transferred into edible vegetables and soil invertebrates. Dioxins and furans showed lower transfer than PCB. Concentrations measured in green fodder collected in the field, and in edible vegetables cultivated in the laboratory exceeded in some cases the European threshold values for undesirable substances. Bioconcentration factors (BCF) for POPs were compared in the tested organisms. PCB transfer into vegetables depended on the number of chlorine substitutes and type of vegetables (BCFzucchini> BCFlettuce> BCFroot> BCFbean). This trend was not observed for PCB with earthworms, whereas in snails, lower BCF were evidenced for highly chlorinated PCB. Use of Modul’ERS multi-media model highlighted parameters with high sensitivity in human exposure through vegetables intake and soil ingestion. Due to lower PCDD/PCDF transfer into vegetables, child exposure was highly dominated by amount of ingested soil. Considering vegetables intake, human exposure globally depended on the number of chlorine substitutes with high PCDD/PCDF contribution in root vegetables, and with a variable PCB contribution according to the type of vegetables. Due to different toxicity values for POPs, health risks were not directly related to exposure with a major contribution of PCDD/PCDF despite of their low soil concentration and low transfer into edible vegetables. Concerning risk assessment for ecosystems, the multi-media model TerraSysTM showed the high sensitivity of BCF values between soil and invertebrates. Use of maximal BCF values when a wide range was experimentally acquired helped not to underestimate POP transfer to the higher links in trophic chain. Use of a simple conceptual model was possible to foresee POP transfer into the ecosystem as far as two levels of predators were at least considered. These studies help to identify common steps and tools between Human Health and ecosystems risk assessments as environmental studies need to be promoted and structured.of PCB and PCDD/F from soil to the terrestrial ecosystem with potential risk assessment for Humans and for the ecosystems.