Microbial metabolism in wormcast affected the perturbation on soil organic matter by microplastics under decabromodiphenyl ethane stress.

Large-scale plastic wastes annually inevitably induce co-pollution of microplastics (MPs) and novel brominated flame retardants (NBFRs), while gaps remain concerning their effect on terrestrial function. We investigated the impact of polylactic acid (PLA) or polyethylene (PE) MPs after aging in soil-earthworm microcosms under decabromodiphenyl ethane (DBDPE) contamination. MPs altered the food (i.e. soil) of earthworms and affected cast composition, which in turn further affected soil function. After 28 days of exposure, MPs, especially UV-aged MPs, caused the significant enrichment of plastics-degrading bacteria and C/N cycling functions in wormcast, with increased dissolved organic matter consumption after co-exposure (1 % MPs accompanied by 10 mg kg DBDPE). Aging significantly affected soil carbon sequestration, while its effects varied depending on the types of MPs. Notably, soil organic matter was the most impactor affecting wormcast bacteria, highlighting the importance of earthworm's activity on soil carbon. In comparison, PLA-MPs induced stronger responses to the C/N cycling process based on its biodegradable property than PE-MPs, however, aging had a greater effect on PE-MPs due to the formation of oxygen molecules from nothing in the structure. This study expands our current understanding of the interactions of aged MPs and DBDPE in the terrestrial ecosystem. SYNOPSIS: This study highlighted that both MPs before and aging altered the bacterial communities in wormcast and further affected soil ecology during earthworm feeding and excretion.