Heavy Metal Determination and Risk Assessment of Selected Mushroom Species and their Substrates in South-eastern Nigeria
Abstract
Heavy metals (HMs) contaminate the environment and pose significant health risks to humans through accumulation in ecosystems, leading to toxicity and various diseases. This study assessed heavy metal contamination and associated risks in selected mushroom species and their substrates across southeastern Nigeria. Using a stratified random sampling approach, representative mushroom and substrate samples were collected from five states: Abia, Anambra, Ebonyi, Enugu, and Imo. Soil chemical properties were analyzed using standard methods, while heavy metals were determined using an Atomic Absorption Spectrophotometer (Varian Spectra AA 200). Data were subjected to analysis of variance (ANOVA), and significant means were separated using Duncan’s Multiple Range Test (DMRT) at a 5% probability level. Results showed significant variations in heavy metal concentrations (Pb, Ni, Cr, Fe, and Cd) in both mushrooms and substrates, as well as in soil chemical properties (pH, organic carbon, organic matter, total nitrogen, total phosphorus, electrical conductivity, and cation exchange capacity) across species and sampling locations. The distribution of heavy metals followed the order Fe > Pb > Ni > Cr > Cd in oyster mushrooms and Fe > Pb > Ni > Cd > Cr in Agaricus species. Ebonyi State recorded the highest contamination levels for most heavy metals (Pb, Ni, Cd) in oyster mushrooms, followed by Anambra (Fe) and Abia (Cr). Similarly, Agaricus mushrooms from Ebonyi showed the highest contamination for Pb, Ni, Cr, and Cd, while Anambra recorded higher levels of Fe. For substrates, Agaricus samples from Enugu exhibited the highest pollution levels, whereas oyster mushroom substrates showed higher contamination in Abia (Pb and Cd) and Ebonyi (Ni), followed by Anambra (Fe). Although most risk assessment results indicated non-contaminated to low contamination levels suggesting that the studied locations are relatively safe continuous monitoring of heavy metal concentrations in biological tissues is recommended to prevent long-term bioaccumulation.