Impact of co-occurrence of microplastics and lindane on lindane biodegradation and soil carbon cycling in flooding environments

Microplastics (MPs) influence organic pollutant adsorption and desorption in the soil environment. However their effects on the biodegradation of these pollutants and the cycling of essential soil elements remains poorly understand. Hence, a particle size of 150 μm polyethylene microplastics (PE MPs) containing lindane (γ-HCH) were cultured in sealed serum bottles and incubated for 60 days to track their interaction on the influence of biodegrading of γ-HCH biodegrading and sorption, as well as the carbon cycling under submerged anaerobic conditions. Results showed the degradation ratio of γ-HCH was significantly faster in the PE MPs-soaked γ-HCH treatment (79.05 %) compared to the γ-HCH-only (37.65 %) and PE MPs-mixed γ-HCH (34.94 %) treatments after 10 days incubation. The presence of lindane significantly stimulated greenhouse gas production under anaerobic conditions. By day 30, in the PE MPs-mixed γ-HCH treatment, the concentrations of CH and CO reached 81.01 and 107.23 mmol/L, respectively. In the γ-HCH-only treatment, the corresponding concentrations were 62.77 and 84.33 mmol/L. Additionally, dissolved organic matter (DOM) analysis revealed changes in composition and humification indices (HIX, BIX, FI, FrI) due to the co-existence of PE MPs and γ-HCH. Microbial community analysis revealed that the co-occurrence of PE MPs and γ-HCH significantly influenced soil bacterial structure and diversity. Notably, Bacteroidetes_vadinHA17, Desulfosporosinus, Nocardioides, Micrococcales, Acidimicrobiia, Propionibacteriales, Gemmatimonadales and Myxococcota were significantly enriched in the PE MPs-mixed γ-HCH treatments on day 10, while only the WS4 and Micrococcales were significantly enriched on day 60. Overall, our study demonstrated that the addition of lindane significantly stimulated the production of CH and CO and this effect was further enhanced by the co-occurrence of lindane and PE MPs, which provides valuable insights into the behavior of MPs and pollutants co-contamination and their impact on the soil carbon cycle.