Interactions of micro-/nanoplastics and engineered nanomaterials in the environment and the toxicity of co-exposure

Colloidal particles play a critical role in material fluxes in the environment. They are ideal carriers of pollutants and pathogens, exhibiting "trojan horse" or "vector" effects because of their high relative surface activity and area. Due to increasing production, wide application, and high waste volumes, the contribution of microplastics (MPs), nanoplastics (NPs), and engineered nanomaterials (ENMs) to environmental contamination has skyrocketed and is changing the characteristics of the colloidal material pool, creating an ecological burden that is compounded by the durability of plastics and reactivity of ENMs. Their inevitable interactions through physical, chemical, or biological mechanisms, such as heteroaggregation, redox reactions, and/or altered toxicity pathways, may exacerbate the adverse ecological and health impacts of these contaminants. However, interactions between MPs/NPs and ENMs in the environment and the resulting toxic effects remain largely unexplored. This review evaluates the ecological and health risks of co-exposure to MPs/NPs and ENMs with the following goals: 1) to summarize the state-of-the-art understanding about the physical, chemical, and biological interactions between MPs/NPs and ENMs that result in altered properties and enhanced or diminished stress; and 2) to identify knowledge gaps of current research in a real-world environmental or biological context and address the need for future research to shift from reliance on model materials (e.g., polystyrene) under laboratory conditions to materials with higher environmental relevance (e.g., polyethylene and polypropylene) under field conditions.