Biomass production and heavy metal uptake by crops grown in two contrasting soils amended with sewage sludge

The application of sewage sludge (SS) to agricultural soils offers a sustainable solution for waste management, allowing nutrient recycling through crop production. Heavy metals (HMs) in SS can accumulate in soils and crops, posing risks to the environment and bioaccumulation in the food chain. This study investigated the impact of SS amendment on biomass production, HMs uptake (As, Cd, Cr, Cu, Ni, Pb, and Zn) by four crops (chicory, tobacco, tomato and sorghum), and soil properties (pH, electrical conductivity, and HMs content) in a greenhouse experiment. A set of 4.5 L pots were filled with soil-sludge mixture for Typic Argiudoll (S1) and Typic Hapludoll (S2) soils at a 1.56% SS-soil dry weight ratio. Sewage sludge treatment reached 39 Mg ha−1 of dry SS. The amendment increased biomass production by 2.9–3.1 folds in chicory and tobacco respectively. All crops took up higher amounts of HMs from soils after SS application. Heavy metals concentrations in plant tissues remained below phytotoxic levels and crops were safe for consumption. At post-harvest, SS addition to S1 (acid soil) increased pH but reduced pH of S2 (alkaline soil). Electrical conductivity increased in S1 soil with SS. Soil HMs concentrations after SS application met agricultural regulations. Under these conditions, applying SS to agricultural soils represents a safe disposal procedure. Additionally, as different crops led to varying residual HMs concentrations, we suggest crop rotations to improve SS application sustainability. Monitoring the evolution of HMs levels in soils and plants under field conditions with extended SS land application remains essential to protect and preserve long-term soil health.