Research progress on the sources and toxicology of micro (nano) plastics in environment

Micro- and nanoplastics are plastic particles which are widely distributed in the environment. The pollution status and toxicity of micro- and nanoplastics in various environment matrices have attracted increcesing attention in recent years. In this review, we systematically assess the current literature on the sources and occurrences of micro- and nanoplastics in the environment and their potential impacts on marine organisms. We also discussed the potential human health effect of micro- and nanoplastics by uptake kinetics and toxicity assessment, and the toxic effects of the typical pollutants caused by micro- and nanoplastics. The results show that the sources of micro (nano) plastics in the terrestrial environment are mainly sewage sludge application, residues of plastic products used in agriculture, irrigation water contaminated by microplastics and/or aerial deposition. The micro (nano) plastics enter marine environment mainly by land input, seaside tourism, navigation shipping, marine farming and/or aerial deposition. In the marine environment, micro- and nanoplastics can be transported and accumulated through an aquatic food chain from lower trophic level to higher ones, and disturb the metabolism and propagation of the organisms. The toxicity of micro- and nanoplastics is dependent on the size and functional groups on the surface of plastic particles. In general, nanoplastics with smaller size might more easily penetrate and aggregate in cells and tissues and positively charged nanoplastics pose distinct effects on the physiological activity of the cells. Besides, the release of organic pollutants adsorbed on the plastic particles pose more serious toxic effects than the plastics themselves. We hope this review can provide effective support for systematic risk assessment and toxicology of micro- and nanoplastics in future research.