Effects of microplastics on marine copepods

Microplastic contamination has been considered as a global environmental problem in marine ecosystem. Due to small size (< 5 mm) in overlapping with that of microalgae, microplastics can easily be ingested by a wide range of marine copepods both in the laboratory and in situ. Although many studies have reported adverse effects of microplastics on marine copepods, it still lacks a systematic overview about the bioavailability of microplastics and their potential ecological consequences. As copepods dominate zooplankton biomass and provide an essential trophic link in marine ecosystem, this review indicates the bioavailability and toxicity of microplastics in such taxon depend on the shape, size, abundance, and properties of plastics. Also, ours is purposed to tease out the possible molecular mechanisms behind. Microplastic ingestion is prevalent; they impede food intake, block the digestive tract, and cause physiological stress in copepods (e.g., immune responses, metabolism disorders, energy depletion, behavioral alterations, growth retardation, and reproduction disturbance). Notably, in response to microplastic exposure, the copepods show both species- and stage-specificity. Furthermore, microplastics can serve as vectors of organic contaminants (e.g., triclosan, chlorpyrifos, and dibutyl phthalate) and thus increase their toxicity in marine copepods, consequently aggravating the adverse impacts of microplastics in marine ecosystem. Given that most previous studies have partially used pristine microplastics and their shortterm exposure might have undervalued their negative effects, more multigenerational mechanistic researches (for example, via an integration of omics-based technology and phenotypic trait analysis) are urgently required for numerous marine copepods exposed to environmental-characteristics plastics as demonstrated by aged microplastics at environmentally realistic concentrations and added with other environmental pollutants; thus it will not only provide mechanistic insights into the biological impacts of microplastics, but also help make the seawater-benchmark setting and ecological assessment for microplastic pollution in marine environment.

微塑料污染已被视为海洋生态系统中的一个全球性环境问题。由于其尺寸小（<5毫米）与微藻相近，微塑料在实验室和自然环境中都很容易被多种海洋桡足类动物摄入。尽管许多研究已经报道了微塑料对海洋桡足类动物的不良影响，但仍然缺乏关于微塑料的生物可利用性及其潜在生态后果的系统性综述。由于桡足类动物在浮游动物生物量中占主导地位，并在海洋生态系统中提供了重要的营养联系，本综述表明微塑料在此类分类群中的生物可利用性和毒性取决于塑料的形状、大小、数量和性质。此外，我们的目的是梳理出背后可能的分子机制。微塑料的摄入很普遍；它们阻碍食物摄取，堵塞消化道，并在桡足类动物中引起生理应激（例如，免疫反应、代谢紊乱、能量耗尽、行为改变、生长迟缓以及繁殖障碍）。值得注意的是，在应对微塑料暴露时，桡足类动物表现出物种特异性和发育阶段特异性。此外，微塑料可作为有机污染物（例如，三氯生、毒死蜱和邻苯二甲酸二丁酯）的载体，从而增加它们对海洋桡足类动物的毒性，进而加剧微塑料在海洋生态系统中的不良影响。鉴于以往大多数研究部分使用了原始微塑料，且其短期暴露可能低估了它们的负面影响，对于许多暴露于具有环境特征的塑料（如在环境相关浓度下老化的微塑料，并添加了其他环境污染物）的海洋桡足类动物，迫切需要更多多代机制研究（例如，通过整合基于组学的技术和表型特征分析）；这样不仅将为微塑料的生物影响提供机制方面的见解，还有助于为海洋环境中的微塑料污染制定海水基准和进行生态评估。