Ecotoxicological effects of traditional and emerging microplastics on marine zooplankton: A review

Microplastics (MPs) are widespread and persistent pollutants in marine environments, raising global ecological concerns. Zooplankton are a critical group for assessing the broader ecosystem effects of MPs, as their ingestion of MPs can disrupt energy transfer across trophic levels. The toxicity of MPs is influenced by a range of physicochemical characteristics, including particle size, shape, degree of weathering, polymer composition, surface functional groups, incorporated additives, and interactions with other contaminants in the water column. Despite this complexity, studies that systematically evaluate how these factors contribute to toxicity remain limited. In addition, several emerging polymer-based particles-such as tire-wear particles (TWPs), antifouling paint particles (APPs), and bioplastic-derived MPs (BMPs)-are increasingly detected in marine environments. However, despite their potential toxicological risks to marine biota being comparable to or greater than those of conventional MPs, they are often overlooked in reviews addressing the ecological effects of MPs on marine ecosystems. Here, we examine the molecular-level toxic responses of marine zooplankton to MPs, focusing on mechanisms such as metabolic interference, oxidative stress, immunotoxicity, and neurotoxicity, as well as the key physicochemical properties that influence MP toxicity. We further extend the discussion beyond conventional MPs to include emerging MPs, emphasizing their potential ecological implications. Collectively, this review provides a comprehensive understanding of the ecological impacts of MPs on marine zooplankton and underscores the need to move beyond treating MPs as a single, uniform class of pollutants.