Shallow lakes and ponds, providing essential ecological and environmental services, are simultaneously disrupted by various pollutants of emerging concern (PECs). As a group of PECs, microplastics (MPs) ubiquitously found in freshwater are toxic to a huge variety of organisms. However, the consequence of secondary factors such as food quantity determining MPs toxicity, and the corresponding water safety risks await assessment is still poorly understood. Accordingly, we investigated how MPs across three particle sizes (10, 1 and 0.07 µm) interacted with food abundance to affect survival, reproduction and population performance in the waterflea Daphnia magna. Across multiple population traits, we found that MPs toxicity on Daphnia population performance was attenuated by higher food quantity, but this attenuation size was strongly dependent on MPs size. Path analysis results showed population growth rate was mainly constrained by reduced survival rather than fecundity. Furthermore, the additive null model revealed that the interactive effects of food abundance and MPs were predominately recognized as synergism and trait dependency. The present findings underscore the importance of considering the complexity of interactions that can occur in the wild, when assessing the effects of plastics pollution on population dynamics of the basic trophic level in lakes and ponds.

提供基本生态和环境服务的浅水湖泊和池塘同时受到各种新兴关注污染物 (PEC) 的干扰。作为一组 PEC，在淡水中普遍存在的微塑料 (MPs) 对多种生物具有毒性。然而，食物数量等次要因素决定 MPs 毒性的后果，以及相应的水安全风险等待评估仍然知之甚少。因此，我们研究了三种粒径（10、1 和 0.07 µm）的 MPs 如何与食物丰度相互作用，从而影响水蚤 Daphnia magna的生存、繁殖和种群表现。在多个种群特征中，我们发现 MPs 对水蚤的毒性较高的食物量会削弱种群表现，但这种衰减大小很大程度上取决于 MP 的大小。路径分析结果表明，种群增长率主要受到存活率降低而非繁殖力的限制。此外，加性无效模型显示，食物丰度和 MPs 的交互作用主要被认为是协同作用和性状依赖性。目前的研究结果强调了在评估塑料污染对湖泊和池塘基本营养级种群动态的影响时，考虑野外可能发生的相互作用的复杂性的重要性。