Contaminated agricultural soils: Trace-elements speciation, their phytoavailability and their uptake by flax plants

Abstract
Flax seeds are used in animal food because of their high content in Omega 3. A number of trace-elements (TEs) - essential as micronutrients, however toxic at supraoptimal concentrations - can accumulate in this plant at quantities incompatible with their introduction in food chain. In order to control this risk and evaluate the uptake of TEs, it is necessary to assess the contents of various species of TEs in soils and plants (each organ and total contents). We were mainly interested in evaluating the availability of Cd, Cu, Ni, Pb and Zn in soils on which flax were grown. Two situations have been compared: the first corresponds to fields into which some sewage sludge were brought in agronomie doses and the second corresponds to plots of land irrigated by waste water over a 100 years period. We are currently performing TEs extractions from soils and plants using different methods : the data of sequential and total extractions (assisted by microwaves) are presented. We have studied two flax varieties in four stages of culture (sowing, stage 10cm. tlowering, maturation). The content, speciation of TEs in soils as well as their transfer in flax seeds are discussed.