Effects of virgin microplastics on the transport of Cd (II) in Xiangjiang River sediment.

River sediments are considered as sinks of microplastics (MPs). Although numerous studies have been conducted on MPs pollution in river sediments, the impact of MPs on the environmental behavior of Cd (II) in river sediments is still unknown. In this work, the effects of six MPs (polyethylene, polypropylene, polystyrene, polyvinyl chloride, polymethyl methacrylate and polylactic acid) on the adsorption of Cd (II) by Xiangjiang River sediment and the transport of Cd (II) in sediment were studied. The results showed that the adsorption ability of sediment to Cd (II) decreased with the increase of the content of MPs in sediment. When the content of MPs in sediment increased to 10%, polypropylene had the greatest effect on the adsorption affinity of sediments to Cd (II). Moreover, the addition of MPs accelerated transport of Cd (II) in sediment, and the transport of Cd (II) in sediment increased with the increase of the content of MPs. The reason may be that after adding MPs, the adsorption capacity of sediment to Cd (II) decreases, and the mass transfer resistance of Cd (II) to sediment reduces, which leads to faster transport of Cd (II) in sediment. Especially, when the content of MPs in sediment increased to 10% (w/w), the saturation point of the breakthrough curve decreased by about 70 pore volumes. This work hopes to provide helpful views on the environmental behavior and risk assessment of Cd (II) in the presence of MPs.