Microplastics intake and excretion: Resilience of the intestinal microbiota but residual growth inhibition in common carp.

Aquatic animals can be influenced by exposure to microplastics (MPs), but little is known about their recovery capacity following MPs excretion. Here, common carp were exposed to environmentally relevant concentrations of MPs for 30 days and followed by MPs excretion for another 30 days. Growth, isotopic and elemental compositions and intestinal microbiota were investigated. We found that fish growth was not influenced by exposed to MPs but was significantly reduced following MPs excretion, indicating a delayed effect on growth. MPs intake and excretion, however, had no obvious effects on isotopic and elemental compositions. MPs altered the community structure and composition of intestinal microbiota and might reduce functional diversity. After MPs excretion, interestingly, bacterial community structures of MPs treatments were grouped together with the control, suggesting the general resilience of fish intestinal microbiota. Nevertheless, high abundance of pathogenic Shewanella, Plesiomonas and Flavobacterium was observed in MPs treatments but did not affect the functional potential of intestinal microbiota. The results of this study provide new information for the application of adverse outcome pathway (AOP) in MPs, suggesting the necessity of paying attention to recovery assay following MPs intake in the development of AOP frameworks.

Ecological stoichiometric and stable isotopic responses to microplastics are modified by food conditions in koi carp.

Microplastics (MPs) can be easily taken up by a wide range of aquatic animals and cause blockage of the digestive tract leading to starvation. Meanwhile, aquatic organisms are facing threats posed by food restriction in both wild and cultured environment. Little knowledge, however, exists on how MPs interact with food conditions to affect aquatic animals. Here, koi carp were exposed to polystyrene MPs (0, 100 or 1000 µg/L) under controlled feeding (satiated or starved) for 30 or 60 days. MPs reduced and interacted synergistically with food conditions on growth after 30 days but antagonistically after 60 days. MPs reduced crude lipid and carbohydrate but increased and antagonistically interacted with feeding conditions on crude protein. Food conditions interacted with MPs on C, N and P but stoichiometric responses were decoupled with macromolecules changes. Food conditions antagonistically interacted with MPs on δ13C after 60 days. Linear discriminant analysis revealed that C:P and N:P were the two most important measured parameters accounting for the response of koi towards MPs and food restriction, presenting an antagonistic interaction of MPs and food status with the prolonged exposure duration.

Single and combined effects of microplastics and cadmium on the cadmium accumulation, antioxidant defence and innate immunity of the discus fish (Symphysodon aequifasciatus).

Microplastics (MPs) have the potential to interact with the toxicity of other common environmental contaminants, such as heavy metals. Here, we investigated the impacts of polystyrene-MPs (32-40 µm), cadmium (Cd) and their combination on early juveniles of the discus fish (Symphysodon aequifasciatus) in relation to Cd accumulation, antioxidant defence and innate immunity. Animals were exposed to three concentrations of MPs (0, 50 or 500 µg L-1) crossed with two levels of Cd (0 or 50 µg L-1) for 30 days. Our findings showed that MPs and Cd had no adverse effects on growth and survival. Under exposure to Cd, however, accumulation of Cd in the body of fish decreased with increasing MP concentrations as supported by a reduced metallothionein content. The activities of superoxide dismutase and glutathione peroxidase increased with MPs but decreased with Cd. MPs, Cd or the mixture increased catalase activity, despite an antagonistic interaction between the two stressors. Glutathione levels increased when exposed to high MP concentrations but decreased when co-exposed to Cd. Malondialdehyde content was only influenced by MPs and increased with elevated MPs. MPs or Cd alone did not increase protein carboxyl content but showed a synergistic effect and increased content. MPs or Cd alone showed no effect on lysozyme activity but had a synergistic effect and activated activity. Activities of both acid phosphatase and alkaline phosphatase were enhanced by MPs, Cd or their mixture, although there was an antagonistic interaction between the two stressors. In contrast, MPs, Cd or their mixture decreased complement 3 content, despite an antagonistic interaction between the two stressors. Collectively, this study suggests that exposure to Cd led to reduced Cd accumulation in the presence of MPs. Nevertheless, co-exposure could induce severe oxidative stress and stimulate innate immunity in the juvenile S. aequifasciatus.