Effects of polystyrene micro/nanoplastics on liver cells based on particle size, surface functionalization, concentration and exposure period

Authors: BANERJEE, AMRITA - Fount Bio; Billey, Lloyd; McGarvey, Amy; Shelver, Weilin

Submitted to: Science of the Total Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/27/2022
Publication Date: 5/2/2022
Citation: Banerjee, A., Billey, L.O., Mcgarvey, A.M., Shelver, W.L. 2022. Effects of polystyrene micro/nanoplastics on liver cells based on particle size, surface functionalization, concentration and exposure period. Science of the Total Environment. 836:155621. https://doi.org/10.1016/j.scitotenv.2022.155621.
DOI: https://doi.org/10.1016/j.scitotenv.2022.155621

Interpretive Summary: Plastic wastes that disintegrate into micro- or nanoplastics have increasingly been detected in the environment, and notably in food and water used for human consumption. However, the possible adverse effects of micro or nanoplastics after ingestion are largely unexplored. We studied the interactions of micro/nanoplastics with liver cells grown in the laboratory in order to determine potential toxicity and to identify potential causes of toxicity. Micro/nanoplastics differing in size, surface property, and dose were tested on cells using exposure periods up to 24 hours. We concluded that small particle sizes having positive surface charge were more toxic than larger particles with either no charge or negative charge on the particle surface. Data from cell-based studies will inform the design of studies to determine the extent of micro/nanoplastic absorption and distribution in food animals. Such studies are useful to regulatory agencies responsible for the conduct of risk assessments associated with human exposures to contaminants that may be present in human food.

Technical Abstract: Small sized plastic waste including micro/nanoplastics (MP/NP) have contaminated our food and drinking water but their impact on health has not been well-documented. Given that the liver is one of the first organs that ingested MP/NP encounter and the organ has a major role in clearance of xenobiotics, the effects of polystyrene MP/NP on liver HepG2 cells was studied. Cellular responses to particles of various sizes (50 – 5000 nm) and surface functionalization (aminated, carboxylated or non-functionalized) were determined at different concentrations (= 100 µg/mL) and exposure periods (= 24 h). Smaller sized particles (50 nm) were internalized by HepG2 cells more avidly than larger particles (1000 nm); the highest uptake being for 50 nm aminated particles (49.2%). Confocal microscopy images of cells corroborated quantitative uptake results. Aminated particles were more toxic to the cells compared to carboxylated or non-functionalized particles. Among aminated particles, an inverse relation between size and toxicity was observed; wherein smaller particles (50 and 100 nm) were more detrimental to the cell viability compared to larger particles (1000 or 5000 nm). Treatment with the particles for 4 h increased intracellular concentrations of Caspase-3 (a late-stage apoptosis marker) by 1.5 – 2.8 fold compared to no particle treatment, but 24 h exposure to the particles attenuated Caspase-3 concentrations. A general trend of a higher Caspase-3 concentration in cells treated with larger particles (500 – 5000 nm) compared to smaller particles (50 – 200) was observed, indicating that bigger particles are more likely to direct cells toward apoptotic cell death upon 4 h exposure. On the other hand, 24 h exposure of cells to large PS particles (500 – 5000 nm) upregulated interleukin 8, a key pro-inflammatory cytokine. Overall, the study demonstrated that smaller aminated particles were most toxic to hepatocytes, but larger particles induced apoptotic cell death or an inflammatory response depending on the length of exposure.