Ecotoxicology of microplastics in water ecosystems and aquatic organisms: A review of synergistic and antagonistic effects of microplastics on other xenobiotics

Microplastics (MPs) are a serious threat to aquatic ecosystems as pervasive environmental pollutants. MPs originate from both primary and secondary sources and enter water bodies through multiple pathways. Over time, their structure changes due to physical erosion, chemical reactions, and biological activity. Due to their large surface area and hydrophobic nature, MPs can adsorb and transport pollutants, such as heavy metals, organic contaminants, and pathogens. Consequently, they play an essential role in determining the fate, bioavailability, and toxicity. MPs can interact with xenobiotics through synergistic, antagonistic, or additive effects. Oxidative stress, endocrine disruption, immune dysfunction, and reproductive impairment were observed in the organisms exposed to MPs. Furthermore, studies showed that these contaminants can be transferred at trophic levels and may biomagnify in higher organisms, including humans, who consume contaminated seafood. Long-term exposure to MPs and their associated contaminants can impact individual organisms, populations, communities, and entire ecosystems by affecting biodiversity, food webs, and the functioning of ecosystems. Therefore, understanding the behavior and interactions of MPs with contaminants is crucial for assessing environmental risks and developing effective strategies to mitigate their impacts. This review identified knowledge gaps in the mechanistic understanding of MP-pollutant interactions, emphasizing the need for standardized ecotoxicological assays.