Cleansing Tannery Effluent with Pleurotus opuntiae: A Green Solution for Environmental Restoration and Toxicity Evaluation

Abstract

Heavy metal contamination has emerged as a global environmental concern, with tannery effluents serving as a significant source of these pollutants. The discharge of tannery effluents (TEs) into natural ecosystems has given rise to a spectrum of catastrophic risks, exacerbating concerns related to public health, safety, and environmental integrity. This current study focuses on the mycoremediation of the heavy metals present in TE, employing the mycelia of Pleurotus opuntiae, an environmentally sustainable solution. The toxicity of TE was rigorously characterized by evaluating a range of physicochemical parameters in accordance with the American Standard and Testing Methods. Subsequently, various diluted concentrations of effluent (25%, 50%, 75% and 100%) were incorporated into MDA media to assess the tolerance index (TI) of P. opuntiae. Notably, the highest TI was observed in the 25% and 50% TE concentrations, while no growth was observed in the 75% and 100% groups due to the exceptionally elevated heavy metal content. P. opuntiae demonstrated remarkable efficacy in heavy metal removal, with the most substantial reductions recorded in the 25% diluted effluent (91.3% Pb, 72.2% Cr and 66.5% Zn), closely followed by the 50% diluted effluent. The highest intracellular bioaccumulation was observed for Pb (17.2 µg/g), outperforming Cr (14.5 µg/g) and Zn (8.5 µg/g) in mycelia grown in 25% diluted effluent. To elucidate the detoxification mechanisms underlying metal removal, various characterizations of the mycelium were conducted, including SEM, FTIR, and XRD analyses. Furthermore, LC–MS analysis shed light on the pivotal role of metabolites in regulating heavy metals within the physiological metabolism of P. opuntiae. Moreover, an upsurge in the concentration of the stress marker, metallothionein, and augmented activity of antioxidant enzymes, like SOD, CAT, LPO and GSH, collectively suggested the significant role of antioxidants in mitigating reactive oxygen species (ROS) and heavy metal toxicity. These comprehensive findings provide a solid foundation for understanding the mechanisms responsible for heavy metal removal by P. opuntiae and pave the way for the development of effective remediation strategies for decontaminating the effluents discharged by the leather industry, contributing to the preservation of our environment and to public well-being.