Effect of different amendments on trace metal bioavailability in agricultural soils and metal uptake on lettuce evaluated by Diffusive Gradients in Thin Films

Abstract

In this study, we have investigated the effect of two different organic amendments on trace metal transfer from soils to crops. Agricultural soils were mixed with (i) biochar (BC) at two levels (3% and 6%, w/w), and (ii) compost at one level (30%, w/w). Lettuce ( Lactuca sativa L.) was planted, and at the end of growth, trace metals (Cd, Cr, Cu, Ni, Pb and Zn) were analysed in both plants and soil. To evaluate the bioavailability and mobility of labile trace metals, different methodologies were used, such as the diffusive gradients in thin films (DGT) technique, BCR sequential extraction and pore water extraction. It has been observed that the lettuces grown in soils with added compost, the amounts of Cd, Cr, Cu and Pb was 1.7, 2.4, 1.3 and 3.7 times lower, respectively, than those found in lettuces planted in soils with no amendment. Moreover, the addition of 3% of BC reduced the uptake of Cr (24%) whereas a 6% of BC reduced Cr (55%) and Pb (50%) levels. Using the DGT technique in soils with different organic matter (OM) content, labile fractions of Cr, Cu and Pb were successfully correlated (p < 0.05) with lettuce total metal concentrations. In conclusion, BCR sequential extraction and DGT method have shown similar efficiency in front other methodologies, although it seems that DGT-methodology is faster and more cost-effective method than sequential extraction for predicting metal uptake by plants. • We tested the effect of biochar and compost applications on metal uptake by lettuce. • Uptake of Cd, Cr, Cu and Pb was 2 to 4 times lower with compost than in nonamended soils. • Biochar produces a greater weight of leaves, roots and total biomass of lettuces. • Biochar also increases leaf length and enhances significantly leaf chlorophyll content. • The effective concentration of Cr, Cu and Pb was significant correlated with metals in lettuce.