Heavy metal content in lettuce plants grown in biosolids compost

The objective of this work was to evaluate the affects of the application of composted biosolids on the accumulation of heavy metals (Cd, Cu, Ni, Pb and Zn) in lettuce leaves. Pots containing different proportions (0 to 100%) of composted biosolids were used to grow lettuce plants under greenhouse conditions. Dry and fresh weight, leaf area and Cd, Cu, Ni, Pb and Zn uptake were determined after harvest. It was found that the dry and fresh matter productions of the plants were significantly lower in the control treatment. The addition of composted biosolids caused a 20 and 40% increase in biomass accumulation. Cd and Pb concentrations in leaves were below detection limits (0.05 mg kg(-1)) in all treatments. Zn concentration in leaves increases as compost proportion decreases, ranging from 57.2 to 80.4 mg kg(-1). Composted biosolids application increased the Cu and Ni plant concentrations, ranging from 5.1 to 9.8 mg Cu kg(-1) and 2.3 to 3.7 mg Ni kg(-1). In all treatments the proportions of heavy metals in plants were below the international standards of toxicity. The results allow us to suggest that, in short-term applications, composted biosolids could be used as soil amendment for lettuce production, without toxic effects in the chemical composition of the plant.