PCBs uptake by carrots after sludge composts application: worst-case and operational practice in greenhouse conditions
Résumé
Polychlorinated biphenyls (PCBs) are classified as priority pollutants by American and European environmental agencies. The most important problem with PCBs is their potential for transmission within the food chain. In France, sewage sludge composts which answer to the French norm NFU 44-095 are applied on arable crops and could be applied on market gardening. A study on PCBs behaviour in a sand/soil - plant system was conducted with the reclamation of sewage sludge compost for market gardening in mind. It was carried out in a temperature and humidity regulated greenhouse. Soil, compost and carrot samples were analyzed. PCBs uptake was followed into carrots core, peel and leaves. First, carrot plants (Daucus carota var. Amsterdam Bejo) were grown on sand + PCBs pure substances in order to study transfer pathways. Two pathways by which PCBs can enter a carrot were identified: (1) uptake and transport in oil channels (2) foliar uptake of vapour from surrounding air. Secondly, carrot plants were grown on amended sand and sandy soil under operational practice. No PCBs uptake was observed from the real operational practice experiment. Indeed, PCBs levels in carrots were lower than the limit of quantification in all cases.
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