Polystyrene (PS) microbeads are the most commonly used microplastics in ecotoxicological studies ( Chae and An, 2017) but PS microbeads are rarely detected in the environment ( Zhang et al., 2018). However, compared to the diversity of microplastics in the environment, microplastics used in these studies are often simple and even hardly found in the environment. Ingestion and egestion of microplastics by aquatic organism have been investigated in many laboratory experiments ( Cole et al., 2016 Lu et al., 2016). Previous work has also considered the egestion of microplastics via feces by variety of organisms, which could affect not only the fate and distribution of microplastics but also their toxic effects on organisms ( Cole et al., 2013 Dawson et al., 2018 Grigorakis et al., 2017 Hämer et al., 2014 Katija et al., 2017 Ory et al., 2018).
In finless porpoise, unintentional ingestion of microplastics has been speculated as the avenue for microplastics found in neonatal porpoise ( Xiong et al., 2018). Filter-feeding fish can ingest microplastics during filtration ( Fossi et al., 2014) while trophic transfer and initiative predation are both potential pathways for microplastics to enter predators and opportunistic feeders ( Ferreira et al., 2018 Grigorakis et al., 2017 Lu et al., 2016 Ory et al., 2018). Ingestion of microplastics by fish can be affected by their feeding habits.
However, factors affecting the ingestion and retention of microplastics in organisms are still poorly understood.
This implies that residence time in organisms as well as the features of microplastics are related to their toxic effects. Direct physical damage from microplastics and adverse effects from hazardous substances released from them might be responsible for the toxicity of microplastics ( Chae and An, 2017 Koelmans et al., 2016 Lu et al., 2016). Microplastic exposure can have physiological, behavioral, growth, reproductive, and genetic impacts on aquatic organisms ( Chae and An, 2017 Green et al., 2017). Aquatic organisms including zooplanktons, benthic macroinvertebrates, fishes, and even marine mammals have been demonstrated to have microplastics detected in their digestive tracts ( Cole et al., 2013 Jabeen et al., 2017 Li et al., 2018a Lusher et al., 2017). Both marine and freshwater ecosystems are considered to be important sinks of microplastics ( Cole et al., 2011 Zhang et al., 2018). Microplastics (plastic particles <5 mm) have become a worldwide environmental concern due to their wide distribution and their potential ecological risks ( Machado et al., 2018 Rochman, 2018). their shape, color, and size) should be considered in future ecotoxicological studies. Thus, the specific features of microplastics (e.g. Results of this study imply that different features of microplastics result in different exposure risks for fish. The presence of food appeared to reduce film and filament residues in fish after 72 h. However, the egestion rate of filaments was the lowest among all tested microplastic shapes. Microplastics ingested by goldfish were egested within 72 h. However, in the presence of food, more green and black microplastics were ingested compared with red, blue, and white microplastics while significantly higher amounts of microplastic films were ingested compared with fragments and filaments. Results showed that goldfish ingested white PE microplastics only in the presence of fish feed and that microplastics larger than 2 mm were rejected even after being ingested. In this study, goldfish ( Carassius auratus) was used to investigate ingestion and egestion of polyethylene (PE) microplastics and how these processes were affected by size, color, and shape of microplastics. It is vital to understand processes of microplastic ingestion and egestion by aquatic organisms in order to evaluate the potential effects and impacts of microplastics in aquatic ecosystems.
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