Roles of polystyrene micro/nano-plastics as carriers on the toxicity of Pb2+ to Chlamydomonas reinhardtii

Abstract

Little information could be consulted on the impacts of micro-plastics as carriers on toxicity of heavy metals, especially for micro-plastics of different sizes. Therefore, this study investigated the adsorption and desorption of Pb2+ on polystyrene plastics with nano- and micro-size (NPs and MPs), and further evaluated the roles of NPs and MPs as carriers on the toxicity of Pb2+ to Chlamydomonas reinhardtii (C. reinhardtii). The results showed that NPs showed higher adsorption capacities and a lower desorption rate for Pb2+ than MPs. The growth inhibitory rates (IR) of mixed and loaded Pb2+ with MPs to C. reinhardtii were 18.29% and 15.76%, respectively, which were lower than that of Pb2+ (22.28%). The presence of MPs decreased the bioavailability of Pb2+ to C. reinhardtii by a competitive adsorption for Pb2+ between MPs and algal cells, and suppressed membrane damage and oxidative stress caused by Pb2+. Maximum IR was observed for the mixture of NPs with Pb2+ (35.64%), followed by Pb2+ loaded on NPs (30.13%), single NPs (26.71%) and Pb2+ (21.01%). The internalization of NPs with absorbed Pb2+ intensified lipid peroxidation. The mixed and loaded microplastics with Pb2+ had more negative effects on C. reinhardtii than the single microplastics. The size-dependent effect was observed in the capacity of heavy metal ions carried by microplastics and the roles of microplastics as carriers on the toxicity of Pb2+. The results showed that the indirect risk of microplastics as 'carriers' could not be ignored, especially for NPs.