Effects of polyethylene microplastics on CHCl₃ and CHBr₃ fluxes and microbial community in temperate salt marsh soil

Microplastics (MPs) affect the carbon cycle in coastal salt marsh soils. However, studies on their effects on CHCl₃ and CHBr₃, which are volatile halohydrocarbons that can damage the ozone layer, are lacking. In this study, indoor simulation experiments were conducted to explore the effects of MPs invasion on the source and sink characteristics of soil CHCl₃ and CHBr₃. The results showed that different concentrations of polyethylene (PE)-MPs promoted CHCl₃ and CHBr₃ emissions. Emission peaks of the two gases appeared on days 3 and 15 during the culture cycle. CHCl₃ and CHBr₃ fluxes were mainly affected by soil physicochemical properties and microbial communities. PE-MPs caused changes in soil properties, microorganisms, and related functional genes. Soil total organic carbon, which was significantly and positively correlated with CHCl₃. Dissolved organic matter, which was one of the main factors affecting CHBr₃, its relative content increased after the addition of PE-MPs. The abundances of Methylocella and Dehalococcoides, which mediate dechlorination reduction, decreased with the addition of PE-MPs. The addition of PE-MPs also significantly varied the abundance of ctrA, which controls dechlorination in soil microorganisms. The gene pceA greatly influenced CHCl₃ emissions. In addition, CHBr₃ flux was influenced by the interactions between sediment redox and microbial co-metabolic reactions under the control of genes such as TC.FEV.OM and soxB. This study provides theoretical and data support for the source and sink characteristics of volatile halohydrocarbons in coastal salt marshes and highlights the environmental hazards of MPs.