Co-occurrence of Microplastics and Hydrophobic Organic Contaminants in Aquatic Environments: Synergistic or Antagonistic Toxicity?

The co-occurrence of microplastics (MPs) and hydrophobic organic contaminants (HOCs) has been widely detected in aquatic environments, and can exacerbate the water pollution systems through interactions, greatly threatening the safety of water ecosystems. However, a comprehensive review of composite water pollution induced by MPs and HOCs, particularly their combined toxicity effects, is still lacking. This review presents recent advances in their sources, distribution, and fate in composite water pollution systems. The interaction mechanisms between MPs and HOCs and the influencing factors are critically discussed. Colloidal microstructures assembled by MPs and HOCs in the water phase are highlighted, and their resulting synergistic or antagonistic toxic effects are evaluated. Oil spills, textile and plastic fabrication industries, and domestic washing processes are the main sources of MPs and HOCs. Various interactions can occur between MPs and HOCs, depending on the characteristics of MPs, aquatic environment conditions, and co-existing substances, with hydrophobic interactions dominating. The presence of surfactants complicates MP–HOC interactions, resulting in formation of diverse colloidal microstructures. Synergistic, antagonistic, or neutral toxicity can be induced by the co-exposure to MPs and HOCs in aquatic organisms, depending on their ingested dosage, behaviors in organisms, and the types of testing organisms. This review integrates up-to-date cross-disciplinary knowledge to provide a holistic understanding of composite water pollution caused by MPs and HOCs, greatly contributing to their environmental hazard prediction and reduction. Clarify co-occurrence of MPs and HOCs in aquatic environments. Elucidate multiple-dimensional MP–HOC interactions and main influence factors. Comprehensively analyze microstructures assembled by MPs and HOCs. Critically evaluate synergistic/antagonistic toxic effects of co-exposed MPs and HOCs. Propose potential research directions, opportunities, and challenges.