Methane oxidation coupling with heavy metal and microplastic transformations for biochar-mediated landfill cover soil

The impact of co-occurring heavy metal (HM) and microplastic (MP) pollution on methane (CH₄) oxidation by methanotrophs (MOB) in landfill cover soil (LCS) and the role of biochar in mediating these collaborative transformations remains unclear. This study conducted batch-scale experiments using LCS treated with individual or combined HMs and MPs, with or without biochar amendment. Differentiation in methanotrophic activities, HM transformations, MP aging, soil properties, microbial communities, and functional genes across the groups were analyzed. Biochar proved essential in sustaining efficient CH₄ oxidation under HM and MP stress, mainly by diversifying MOB, and enhancing polysaccharide secretion to mitigate environmental stress. While low levels of HMs slightly inhibited CH₄ oxidation, high HM concentration enhanced methanotrophic activities by promoting electron transfer process. MPs consistently stimulated CH₄ oxidation, exerting a stronger influence than HMs. Notably, the simultaneous presence of low levels of HMs and MPs synergistically boosted CH₄ oxidation, linked to distinct microbial evolution and adaptation. Methanotrophic activities were demonstrated to affect the fate of HMs and MPs. Complete passivation of Cu was readily achieved, whereas Zn stabilization was negatively influenced by biochar and MPs. The aging of MPs was also partially suppressed by biochar and HM adsorption.