Nanoplastics, a new type of pollutant, exist mainly in the atmosphere in the form of suspended fine particles. They can enter human body through breathing, make contact with respiratory mucosa and lung cells, and affect their physiological functions. Due to their small size and high tissue affinity, nanoplastics can easily adhere to the cell surface, damage the membrane structure, and it is easily endocytosed and accumulated in cells, which can result in abnormality of cell gene expression and regulation, inflammatory reactions and even cancers. 

Dr. XU Mingkai, Dr. ZHANG Qianru and their colleagues from the Institute of Applied Ecology (IAE) of the Chinese Academy of Sciences conducted a joint research, in which they used the human alveolar epithelial (type II) A549 cell line as an in vitro model of respiratory system epithelial cells, and studied the internalization and toxicity of different sized polystyrene nanoparticles (PS-NPs) in lung epithelial cells. 

The research indicates that small sized PS-NPs, compared with large ones, are more easily internalized by A549 cells and show significant cytotoxic effects. The toxicity of PS-NPs is associated with particle size and concentration of PS-NPs. PS-NPs can cause A549 cell cycle S phrase arrest and induce apoptosis, which are both time-dependent.

Further protein and gene analyses reveal that PS-NPs can induce significant up-regulation in expression levels of pro-inflammatory cytokines (e.g. IL-6, IL-8, NF-κB and TNF-α), and induce pro-apoptotic proteins (e.g. DR5, caspase 3, caspase 8, caspase 9, and Cytochrome C), which also increase the expression level of cellular reactive oxygen species (ROS).  

The research also shows that PS-NPs can exert significant toxicological effects on human alveolar epithelial cells through multiple pathways via affecting multiple targets. Exposure time, particle size and exposure concentration are all key factors affecting the toxicological effects.  

The researchers thus suggest that more attention and research must be given to nanoplastics-related air pollution and environmental risks, including their toxicological effects on humans and terrestrial mammals. 

The study entitled "Internalization and toxicity: A preliminary study of effects of nanoplastic particles on human lung epithelial cell" has been published in Science of Total Environment. The study is financially supported by the National Natural Science Foundation of China.