Abstract
<title>Abstract</title> <p> Agricultural residues provide sustainable substrates for mushroom cultivation, but their potential to accumulate toxic metals may compromise food safety. This study evaluated the concentrations of Cd, Cr, Ni, and Pb in <italic>Pleurotus ostreatus</italic> cultivated on cassava peel, maize stalk, paddy straw, cotton stalk, and their combinations supplemented with 0, 5, 10, and 15 g calcium carbonate. Heavy metal concentrations were determined, and non-carcinogenic and carcinogenic health risks associated with mushroom consumption were assessed using hazard quotient (HQ), hazard index (HI), and cancer risk (CR) models. Paddy straw-based substrates accumulated the highest concentrations of Cr, Ni, and Pb, whereas cassava peel-based substrates generally contained higher Cd levels. Increasing calcium carbonate supplementation consistently reduced metal accumulation across most substrate combinations, indicating reduced metal bioavailability under alkaline conditions. The HQ values for individual metals and the cumulative HI remained below the USEPA safety threshold of 1.0 for all treatments, suggesting negligible non-carcinogenic health risks. Although Cd and Ni contributed most to the HI, their estimated dietary exposures remained within acceptable limits. Carcinogenic risk assessment identified Cd and Ni as the primary contributors to lifetime cancer risk, while Cr and Pb made comparatively smaller contributions. Calcium carbonate amendment substantially lowered cumulative cancer risk across the substrates, with the greatest reductions observed at the 15 g supplementation level. The findings demonstrate that agricultural wastes can be safely utilized for <italic>P. ostreatus</italic> cultivation when appropriate substrates are selected and supplemented with calcium carbonate. </p>