Impact of heavy metals in sewage sludge on soil and plants (colza and wheat)

National audienceWe are testing the impact of heavy metals in sludge from urban and industrial wastewater treatment plants. We try to understand their influence on plant growth and their bioaccumulation. We chose two plants: the wheat and rapeseed to their specific characteristics; wheat is a herbaceous low accumulator of heavy metals, however rape (colza) is a plant of the family Brassica napus, is an excellent bio-accumulator of heavy metals. The mean levels found in the soil are organized in the following order: Fe >> Mn> Zn> Pb> Cu> Ni> Co> Cd. The contents of heavy metals in the sludge is made very high and exceed European values allowed for that type of use but remain in the standard NT106 Tunisia. The effects of the contribution of sludge are manifested by a significant increase in the weight gains of the whole plant, these results in a variation of the ratio between the aerial part and roots of the plant; this ratio tends to increase with dose of mud brought in soil increase. The roots of both plants show high levels of Zn even on the ground untreated control. The contents of Ni, Pb and Zn compared to Cu and Co are higher in the roots of rape than wheat