1. The pollution of aquatic systems with microplastics (MPs) affects marine and freshwater fish species worldwide. However, little is known about the size‐dependent retention time of these inert particles. To approach this question, the retention time of MP particles was examined in two freshwater fish species with distinct differences in gastrointestinal morphology: rainbow trout (Oncorhynchus mykiss) with a true stomach, and stomachless common carp (Cyprinus carpio).
2. A special diet was developed that contained environmentally relevant concentrations of MPs with sizes ranging from 20 to 1,000 µm. The two species were exposed to three different concentrations and numbers of retained particle were determined up to 72 hr after administration.
3. The results revealed significant differences in retention time between large and small MP particles in rainbow trout, in which the T₅₀ value (time for 50% of particles to be evacuated) ranged from 12.1 hr for 42.7 µm particles to 4.0 hr for 1,086 µm particles. In contrast, the differences observed between sizes in common carp were considerably smaller, with T₅₀ ranging from 7.3 hr for 42.7 µm particles to 4.6 hr for 1,086 µm particles.
4. It is therefore concluded that large particles in rainbow trout must be actively transported out of the stomach, as the evacuation times are significantly shorter than those for food. Small particles, however, are passively excreted with the chyme. In common carp, the evacuation rates of all particle sizes were in the range of that for food, suggesting a passive excretion.
5. The results are particularly relevant in the contexts of particle transfer through the food chain, the release of toxic chemicals, and the translocation into tissues and organs. For this reason, it is essential that the particle size is given more consideration in future studies of microplastics in aquatic environments.

中文翻译：

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鱼类中的塑料微粒疏散取决于颗粒大小

1. 水生系统受到微塑料（MPs）的污染影响着全世界的海洋和淡水鱼类物种。但是，对于这些惰性颗粒的尺寸依存时间知之甚少。为了解决这个问题，我们检查了两种淡水鱼类在胃肠道形态上有明显差异的MP颗粒的保留时间：真胃的虹鳟鱼（Oncorhynchus mykiss）和无胃的鲤鱼（Cyprinus carpio）。
2. 开发了一种特殊的饮食，其中包含与环境有关的MP浓度，尺寸范围为20至1,000 µm。将这两种物质暴露于三种不同的浓度，并在给药后长达72小时确定残留颗粒的数量。
3. 结果表明，虹鳟鱼中大和小MP颗粒之间的保留时间存在显着差异，其中T ₅₀值（50％的颗粒被抽空的时间）范围从42.7 µm颗粒的12.1小时到1,086 µm颗粒的4.0小时。 。相反，观察到的鲤鱼大小之间的差异要小得多，T _50的范围从42.7 µm颗粒的7.3小时到1,086 µm颗粒的4.6小时。
4. 因此得出结论，虹鳟鱼中的大颗粒必须主动从胃中运出，因为疏散时间明显短于食物。但是，小颗粒会与食糜一起被动排泄。在鲤鱼中，所有粒径的疏散率都在食物的范围内，表明是被动排泄的。
5. 在颗粒通过食物链转移，释放有毒化学物质以及易位到组织和器官中的情况下，结果特别重要。因此，在未来水生环境中对微塑料的研究中，必须对粒度进行更多的考虑。