The widespread occurrence and accumulation of micro- and nanoplastics in aquatic environments has become a growing global concern. Generally, natural aquatic populations are characterized by a variety of multi-structured age groups, for which physiological and biochemical responses typically differ. The freshwater cladoceran, Daphnia pulex, is a model species used extensively in environmental monitoring studies and ecotoxicology testing. Here, the effects of a polystyrene nanoplastic on the physiological changes (i.e., survival) and expression levels of stress defense genes (i.e., those encoding antioxidant-mediated and heat shock proteins) in this freshwater flea were measured. Results from acute bioassays were used to determine the respective nanoplastic LC50 values for five age groups (1-, 4-, 7-, 14- and 21-day-old individuals): the obtained values for the 1- and 21-day-old D. pulex groups were similar (i.e., not significantly different). The expression levels of genes encoding key stress defense enzymes and proteins—SOD, CAT, GST, GPx, HSP70, and HSP90—were influenced by the nanoplastic in all the age groups, but not in the same way for each. Significant differences were observed among all age groups in their expression of the gene encoding the energy-sensing enzyme AMPK (adenosine monophosphate-activated protein kinase) α, β, and γ following exposure to the nanoplastic. Moreover, the expression of AMPK α was significantly increased in the 1-, 7-, and 21-day-old individuals exposed to nanoplastic relative to the control group. Together, these results indicate that age in D. pulex affects the sensitivity of its individuals to pollution from this nanoplastic, primarily via alterations to vital physiological and biochemical processes, such as cellular energy homeostasis and oxidation, which were demonstrated in vivo. We speculate that such age-related effects may extend to other nanoplastics and forms of pollution in D. pulex and perhaps similar marine organisms.

微米和纳米塑料在水生环境中的广泛发生和积累已成为全球日益关注的问题。通常，天然水生种群的特征是多种多样的年龄段，其生理和生化反应通常有所不同。淡水clacerceran，水蚤，是在环境监测研究和生态毒理学测试中广泛使用的模型物种。在此，测量了聚苯乙烯纳米塑料对这种淡水跳蚤的生理变化（即存活）和应激防御基因（即编码抗氧化剂介导的蛋白和热激蛋白的基因）表达水平的影响。急性生物测定的结果用于确定五个年龄组（1-，4-，7-，14-和21日龄的个体）各自的纳米塑料LC50值：获得的1-和21-日龄的值旧的D. pulex组相似（即，无显着差异）。编码关键逆境防御酶和蛋白质的基因的表达水平-SOD，CAT，GST，GPx，HSP70和HSP90 -were由nanoplastic在所有年龄组的影响，但不是每个相同的方式。暴露于纳米塑料后，在各个年龄组之间观察到了编码能量感应酶AMPK（腺苷一磷酸激活的蛋白激酶）α，β和γ的基因表达的显着差异。此外，相对于对照组，在暴露于纳米塑料的1、7和21天龄个体中AMPKα的表达显着增加。综合起来，这些结果表明D. pulex中的年龄主要通过改变体内重要的生理和生化过程（例如细胞能量稳态和氧化）来影响其个体受到这种纳米塑料污染的敏感性。我们推测，这种与年龄有关的影响可能会扩展到D. pulex和其他类似海洋生物中的其他纳米塑料和污染形式。