Adverse outcome pathways and in vitro toxicology strategies for microplastics hazard testing

The human health impacts of microplastics exposure remain uncertain, though they are of growing global concern. The strategic use of the adverse outcome pathways (AOPs) framework will permit leveraging of existing knowledge on disease mechanisms of other stressors to improve our understanding of the toxicological impacts of microplastics and enable identification of key biological events within a causal framework linking microplastic exposures to adverse outcomes. Here, the AOP framework is briefly described. Considering that inflammation, oxidative stress and cytotoxicity are among the reported outcomes of microplastics exposure in vitro or in vivo and because these key events form the AOP for tissue injury, an adverse key event preceding tissue dysfunction and disease, the review describes a tiered microplastics testing strategy targeting these events. Minimum considerations for in vitro testing of microplastics are also summarised.