Anaerobic oxidation of methane and its potential role in heavy metal(loid) speciation in wetland soils: occurrence, mechanisms and environmental implications

Wetlands deliver essential ecological services but are increasingly threatened by heavy metal(loid)s (HMs) due to anthropogenic activities. The speciation of HMs, which dictates their toxicity and mobility, can be transformed by microbial redox processes like anaerobic oxidation of methane (AOM). However, the contribution of AOM to HM speciation transformation in wetland soils remains inadequately assessed. This review summarizes the current understanding of how AOM couples with the reduction of various elements to directly or indirectly affect HM speciation. These elements include arsenate, chromate, selenate/selenite, antimonate, vanadate, Fe(III), Mn(IV), and sulfate. We examine the responsible microorganisms and their electron transfer pathways, and evaluate the potential for applying these AOM processes in the remediation of HM contamination. These AOM processes can potentially influence the reduction, mobilization, or immobilization of HMs, thereby regulating their biogeochemical cycles in wetland soils. Future research priorities include determining the role of aerobic methanotrophs in these processes, clarifying the impacts of environmental conditions and HM forms, and developing targeted AOM regulation strategies for remediating contaminated wetlands. This work advances the mechanistic understanding of the interactions between HMs and AOM, and provides theoretical insights for developing remediation strategies for HM-contaminated wetland soils.