Effects of microplastic on arsenic accumulation in Chlamydomonas reinhardtii in a freshwater environment

Chlamydomonas reinhardtii plays a critical role in the biogeochemical cycling of arsenic (As) and purification of water bodies contaminated with As. We investigated the effects of microplastic pollution on the ability of C. reinhardtii to accumulate As. We revealed that different sized [100 nm (S) and 5 µm (L)] polystyrene microplastics (PSMP) at different concentrations (50 and 100 mg L^-1) interacted with the phospholipid structure in C. reinhardtii. Dispersion forces disrupted the structure and function of membrane proteins, reducing the accumulation and efflux of As(III) and inhibiting the As(V)-As(III)-MMA-DMA detoxification process in C. reinhardtii cells. The maximum As accumulation rates of C. reinhardtii in the control groups, L50, L100, S50, and S100 treatments were 53.71, 50.95, 48.42, 43.83, and 39.11 μg g^-1 h^-1, respectively. Further, PSMPs and As(III) triggered "oxidative bursts" in cells, damaging cell membranes and reducing chlorophyll content and Rubisco activity. As a result, photosynthesis, respiration, and growth were inhibited. When compared with an absence of PSMP, the addition of L- (S-) sized PSMP to the As-containing solution would result in a lower (higher) impact on C. reinhardtii. Overall, this study demonstrated that microplastics significantly affect As accumulation in C. reinhardtii. Our results indicate that the critical role of this algal species in As cycling in earth's pedo- and hydrosphere may be impeded by microplastic pollution.