Effect of biosolid compost amended on Pb availability in soils cultivated with lettuce

Agricultural soil contaminated with Pb is an issue of increasingly serious concern, with a great impact on crop quality and the associated toxicological risk. This study aimed to evaluate the effect of amending Pb-contaminated agricultural soils with novelty compost on soil fertility, Pb bioavailability for lettuce crops and the associated toxicological risk. Lead-contaminated soil was collected from the vicinity of a secondary smelter and amended with the maximum recommended concentration of compost (10%). Soil physicochemical and fertility parameters, Pb content and its fractionation were compared between amended and unamended contaminated soils over a 40-day incubation period. Then, lettuce was grown in the soil treatments with germination rate, Pb content in tissues and toxicological risk being determined. The compost amendment, together with the incubation period, improved the soil fertility parameters, optimizing nutrient availability for plants while reducing Pb bioavailability by 9.3%. Moreover, lettuce germination was not affected by Pb, showing a high seed tolerance. The young (edible) leaves were more susceptible to metal toxicity and accumulated Pb above the permissible levels in all treatments. Compost amendment of polluted soil reduced Pb accumulation in edible leaves by 50% with a consequent decrease in toxicological risk, although the effect was not sufficient to reach values of crops in natural soils.