The safety of microplastics (MPs) and associated health effects has been one of the major concerns worldwide. However, the role of photoaging toward the risk of MPs in water ecosystems remains inconclusive yet. In this study, the size of polyamide (PA, ∼32.50 μm) MPs was obviously decreased after photoaging in water containing fulvic acid (FA) and humic acid (HA) (∼19.75 and ∼24.30 μm, respectively). Nanoplastics were formed (4.65% and 2.03%, respectively) and hydrophilia and colloidal stability was improved due to the formation of oxygen-containing functional groups. FA-aged PA exhibited higher inhibition on body length and weight of developing zebrafish than HA-aged and pristine PA. Photoaged MPs in intestine were more difficult to be depurated by zebrafish, leading to the disappearance of intestinal folding, shedding of more enterocytes, and emaciation of intestinal microvilli. Dietary lipid digestion in larvae was inhibited by aged PA due to oxidative stress-triggered lipid peroxidation and inhibition of lipase activities and bile acids secretion. Exposure of photoaged MPs down-regulated genes (cd36, dgat1a, dgat2, mttp, etc.) associated with triglyceride resynthesis and transportation, resulting in lipid maladsorption and growth inhibition. Our findings highlight the potential negative effects of environmentally aged MPs on diet digestion and nutrient assimilation in fish.

微塑料 (MP) 的安全性和相关的健康影响一直是全球关注的主要问题之一。然而，光老化对水生态系统中 MPs 风险的作用仍然没有定论。在这项研究中，在含有富里酸（FA）和腐植酸（HA）（分别为~19.75和~24.30μm）的水中光老化后，聚酰胺（PA，~32.50μm）的尺寸明显减小。形成了纳米塑料（分别为 4.65% 和 2.03%），并且由于含氧官能团的形成，提高了亲水性和胶体稳定性。FA 老化的 PA 对发育中的斑马鱼体长和体重的抑制作用高于 HA 老化和原始 PA。肠道光老化 MPs 更难被斑马鱼净化，导致肠道折叠消失，更多肠细胞脱落，和肠道微绒毛消瘦。由于氧化应激引发的脂质过氧化和脂肪酶活性和胆汁酸分泌的抑制，老化的 PA 抑制了幼虫的日粮脂质消化。暴露光老化 MPs 下调基因 (cd36、dgat1a、dgat2、mttp等）与甘油三酯的再合成和运输有关，导致脂质吸附不良和生长抑制。我们的研究结果强调了环境老化的 MPs 对鱼类饮食消化和营养吸收的潜在负面影响。