Corn-derived biochar mitigates oxidative stress and increases the content of essential elements in lettuce leaves...

Phthalic acid esters (PAEs) are recognized markers of microplastic pollution of the environment. The study assessed the effects of different biochars (BC) derived from sewage sludge (SS), corn residues (CR), sunflower (SF), and residues from biogas production (BG) on lettuce grown in PAEs-polluted soil. The BC varied in composition, porosity, and carbon structure, with CR-BC exhibiting the highest surface area and optimal aliphatic carbon content, making it the most effective for soil application. SS had the highest heavy metal and PAHs content, though within safe limits. Elevated phosphate levels in lettuce leaves, influenced by high PAHs, ash, and metal content in BC, were associated with increased CAT activity, indicating oxidative stress. A strong positive correlation was found between Cd and phosphate content, especially in SS-treated plants, and between phosphate and B. CR-BC limited heavy metal uptake while promoting beneficial nutrient interactions (such as between Ca and Mg). PAEs accumulation in lettuce was strongly negatively correlated with phosphate and B levels, suggesting these elements reduce pollutant uptake. Among treatments, CR-BC significantly reduced PAEs accumulation in lettuce leaves, which is critical for food safety. CR-BC also enhanced lettuce biomass, chlorophyll content, and nutrient uptake, and it decreased oxidative stress (lower levels of MDA and enhanced antioxidant enzyme activity of SOD and CAT). Conversely, BG-BC negatively affected plant growth, likely due to its high pH. Overall, the findings highlight the importance of BC feedstock properties, with corn-derived BC offering the most beneficial effects on plant health and pollutant mitigation in polluted soils.