A rapid review and meta-regression analyses of the toxicological impacts of microplastic exposure in human cells

Humans are exposed to microplastics (MPs) daily via ingestion and inhalation. It is not known whether this results in adverse health effects and, if so, at what levels of exposure. Without epidemiological studies, human cell in vitro MP toxicological studies provide an alternative approach to this question. This review systematically synthesised all evidence and estimated thresholds of dose-response relationships. MEDLINE and Web of Science were searched from inception to March 2021 and study quality was rated using a novel risk of bias assessment tool. Seventeen studies were included in the rapid review and eight in the meta-regression. Four biological endpoints displayed MP-associated effects: cytotoxicity, immune response, oxidative stress, barrier attributes, and one did not (genotoxicity). Irregular shape was found to be the only MP characteristic predicting cell death, along with the duration of exposure and MP concentration (mu g/mL). Cells showed varying cytotoxic sensitivity to MPs, with Caco-2 cells (human adenocarcinoma cell line) being the most susceptible. Minimum, environmentally-relevant, concentrations of 10 mu g/mL (5-200 mu m), had an adverse effect on cell viability, and 20 mu g/mL (0.4 mu m) on cytokine release. This work is the first to quantify thresholds of MPs effects on human cells in the context of risk assessment.

Automated summary

This review investigates the thresholds of microplastics (MPs) effects on human cells by synthesizing existing evidence. The study identifies several biological endpoints, such as cytotoxicity, immune response, oxidative stress, and barrier attributes, that are affected by MPs. The sensitivity of cells to MPs varies, with Caco-2 cells being the most susceptible. Additionally, the shape, duration of exposure, and concentration of MPs play a role in determining their effects on cells.