Carbendazim adsorption on polyethylene microplastics and the toxicity mechanisms on cotton plants, soil enzyme activity and rhizosphere bacterial community under combined stress conditions

Polyethylene (PE) and carbendazim are common pollutants in soil, and their individual toxicities have been widely studied. However, there are few reports on PE as a carrier for carbendazim and their combined toxicity to plants and soil. Therefore, in this study, we focused on the adsorption effects of different PE particle sizes (25 μm, 150 μm) at different concentrations (1 %, 5 %, m/m) on carbendazim (2.0 mg·kg⁻¹, 5.0 mg·kg⁻¹) and the combined toxicity to cotton and soil microbiota. The results showed that the carbendazim adsorption by PE followed secondary kinetics and was consistent with the Freundlich model. Due to adsorption, the half-life of carbendazim in soil was extended (from 6.31 d to 14.20 d), and the capacity of carbendazim to control cotton Verticillium wilt was weakened. Combined stress exacerbated the inhibitory effects on cotton biomass, chlorophyll content, soil enzyme activity compared to the individual carbendazim or PE treatments. The high-throughput sequencing analysis indicated that combined stress (5.0 mg·kg⁻¹ carbendazim, 5 % 25 μm PE) significantly reduced the richness and diversity, changed the structural composition of rhizosphere soil bacterial community, and greatly increased the abundance of bacteria with potential degrading functions, such as Marmoricola. Functional and network analysis showed that combined stress altered the soil microbial function and abundance, as well as the network structure and key bacterial groups, decreased the number of positively correlated connections. This study provides a theoretical basis for evaluating the effects of combined PE and carbendazim stress on crops and soils.