Micro(nano)plastics (MPs/NPs) are already present as contaminants in the natural environment globally and have been shown to be difficult to degrade, resulting in the potential for ecological damage and public health concerns. However, the adverse effects of exposure to MPs/NPs by aquatic organisms, especially freshwater microalgae, remains unclear. In the present study, the growth, physiology and transcriptome of the freshwater microalgae Euglena gracilis were comprehensively analyzed following exposure to 1 mg/L of polystyrene (PS) microbeads (5 μm PS-MPs and 100 nm PS-NPs), 0.5 mg/L cadmium (Cd), or a mixture of PS microbeads and Cd for 96 h. Results showed that the toxicity of PS-MPs to microalgae was greater than PS-NPs, inducing increased growth inhibition, oxidative damage and decreased photosynthesis pigment concentrations. PS-MPs alone or in combination with Cd caused cavitation within microalgal cells, as well as increasing the number and volume of vacuoles. The combined exposure toxicity test showed that a combination of Cd + PS-NPs was more toxic than Cd + PS-MPs, which may be explained by the transcriptomic analysis results. Differentially expressed genes (DEGs) in the Cd + PS-NPs group were mainly enriched in metabolism-related pathways, suggesting that algal metabolism was hindered, resulting in aggravation of toxicity. The reduced toxicity induced by Cd + PS-MPs may indicate a response to resist external stress processes. In addition, no adsorption of 0.5 mg/L Cd to 1 mg/L PS microbeads was observed, suggesting that adsorption of MPs/NPs and Cd was not the key factor determining the combined toxicity effects in this study.

微（纳米）塑料（MPs / NPs）已作为污染物存在于全球自然环境中，并且已证明难以降解，从而导致潜在的生态破坏和公共健康问题。但是，尚不清楚水生生物，特别是淡水微藻类接触MPs / NPs的不利影响。在本研究中，淡水微藻Euglena gracilis的生长，生理和转录组在暴露于1 mg / L的聚苯乙烯（PS）微珠（5μmPS-MP和100 nm PS-NPs），0.5 mg / L的镉（Cd）或PS微珠和Cd的混合物中96小时后进行了全面分析。结果表明，PS-MPs对微藻的毒性大于PS-NPs，导致增加的生长抑制，氧化损伤和降低的光合作用色素浓度。单独或与镉结合的PS-MP会在微藻细胞内引起空化，并增加液泡的数量和体积。组合暴露毒性试验表明，Cd + PS-NPs组合比Cd + PS-MPs毒性更大，这可以由转录组分析结果来解释。Cd + PS-NPs组中的差异表达基因（DEGs）主要富含新陈代谢相关途径，表明藻类代谢受到阻碍，导致毒性加剧。Cd + PS-MPs诱导的毒性降低可能表明它对抵抗外部胁迫过程有反应。此外，未观察到0.5 mg / L Cd对1 mg / L PS微珠的吸附，表明MPs / NPs和Cd的吸附不是决定本研究联合毒性作用的关键因素。