Microplastics as a Vector of Hazardous Contaminants: Plastic Chemicals, Digestive Physiology and the Need for Chemical Simplification

Microplastics are one of today’s major environmental problems, as they are a ubiquitous persistent pollutant group that has reached all parts of the environment. The chemical burden of microplastics results from the plastic-associated chemicals (chemical additives, monomers, and non-intentionally added substances) incorporated into the polymer matrix during manufacturing, and the environmental pollutants (e.g., hydrophobic organic compounds, trace metals or pharmaceuticals) that sorb to the plastic surfaces following release. Microplastics have also been shown to be readily ingested by a wide range of organisms across taxonomic groups, and it is this combination of biotic ingestion and chemical association that gives credence to the notion that microplastics may be vectors of hazardous contaminants. Therefore, the transfer of chemicals from microplastics has been the subject of much laboratory research, but owing to the complexity of exposure scenarios, results are often disparate. Moreover, while the relevance of microplastics as realworld vehicles for environmental pollutants has been questioned, recent analysis has shown that plastics can have as many as 16,000 chemicals added to them during manufacturing, many of which are of known toxicity. Furthermore, plastic-associated chemicals once released into the environment may be transformed into distinct substances that exhibit different toxicities compared to their parent compound. This chapter provides an overview of the current literature on microplastics as carriers of environmental pollutants and plastic-associated chemicals, and the emergence of transformation products as a topic of concern. The importance of digestive physiology is recognized as one of the main sites in which chemical release and desorption occurs resulting in chemicals being labile within an organism. Lastly, we explore how the wealth of literature linking microplastics and chemicals has heightened calls for chemical simplification to ensure better safety for environmental (and human) health.