Influence and mechanism of the vertical distribution of Cu, Cd, and Pb at a simulated sediment–water interface covered by degradable microplastics

Currently research on microplastics in the environment focuses on non-degradable microplastics with little attention to research on degradable microplastics. This study involved a 400-day experiment in a simulated lake environment of three degradable microplastics, poly(ε-caprolactone) (PCL), polybutylene succinate (PBS), and poly(butylene adipate terephthalate) (PBAT) at the sediment water interface. Results showed that (1) for the three microplastics, Cd concentration showed a large change from 0 to 20 mm in the water above the sediment interface; the adsorption of Cd, Pb, and Cu in a diffusive gradients thin film (DGT) device are the highest in PBAT micro plastic, followed by PCL and then PBS. (2) Diffuse flux (J) of the three degradable microplastics indicated that Cu, Cd, and Pb in the sediments come from the overlying water that was added to the simulation experiment. (3) Fourier transform infra-red spectroscopy (FTIR) for investigating the adsorption capacity of Cu, Cd, and Pb in the three degradable microplastics showed the absorption peak intensity increased and widened, and some adsorption sites changed. (4) Correlation analysis showed that the factors which most influenced diffusion flux for both water and sediments are oxidation-reduction potential (ORP), followed by organic matter (OM), pH, and electrical conductivity (EC).