Accounting for species traits and exposure complexity to understand organism responses to microplastics and multistressors.

Our understanding of the abundance and hazard of microplastics has rapidly grown in recent years, however experimental studies and subsequent risk assessments largely fail to account for the complexity of microplastics, their interactions with the wider environment, and different species' exposures and responses. Microplastic complexity could lead them to be considered as multistressors in their own right. Uncertainties remain with respect to a) how particle characteristics can alter the hazard they pose (especially polymer type and aging), b) microplastic interactions with the vast array of wider physical, chemical and environmental stressors (multistressors), and c) microplastics' bioavailability and different species responses, especially relating to species traits. In addition, these factors interact to affect exposure, uptake and toxicity simultaneously across ecosystems. The current perspective piece explores the ways in which systems-thinking and targeted, biologically relevant experiments can be implemented to better understand these processes, and their interconnectivity, to progress knowledge of realistic microplastic effects. Without these considerations when designing experiments and interpreting ecotoxicological data, understanding of microplastics as a biological hazard will continue to be oversimplified and unrepresentative of the real environment, impeding our ability to make real, actionable change to solve the plastic pollution problem.