Adverse effects of polystyrene microplastics in the freshwater commercial fish, grass carp (Ctenopharyngodon idella): Emphasis on physiological response and intestinal microbiome.

Microplastics (MPs) pollution in aquatic environment has attracted global attention in recent years. To evaluate the potential toxic effects of MPs in freshwater cultured fish, grass carps (Ctenopharyngodon idella) (body length: 7.7 ± 0.1 cm, wet weight: 6.28 ± 0.23 g) were exposed to different sizes (0.5 μm, 15 μm) and concentrations (100 μg/L, 500 μg/L) of polystyrene microplastics (PS-MPs) suspension for 7 and 14 days, followed by 7 days of depuration, detecting the variations in growth rate, histological structure, oxidative response and intestinal microbiome. Our results indicate that MP toxicity elicited significant size- and concentration-dependent responses by grass carp. MP exposure caused obvious decrease in growth rate on day 14 but not on day 7. Additionally, MPs with large size and high concentration caused more severe intestinal damage and less weight gain, while MP particles with small size and high concentration induced more severe liver congestion and stronger oxidative stress. MP exposure dramatically shifted the gut microbial composition, with the top 10 genera in abundance being associated with the diameter and concentration of the MPs. After 7 days of depuration, only superoxide dismutase and malondialdehyde in liver, showed a tendency to recover to the initial values. Even though the differences in the gut microbial community between the control and treatment groups disappeared, and the proportion of potential pathogenic bacteria in intestine was still high. Thus, it is clear that a short-term depuration period of 7 days is not enough for complete normalization.

Hao Y ，Sun Y ，Li M ，Fang X ，Wang Z ，Zuo J ，Zhang C ... -  《-》

Nano-selenium ameliorates microplastics-induced injury: Histology, antioxidant capacity, immunity and intestinal microbiota of grass carp (Ctenopharyngodon idella).

Microplastics (MPs) are pollutants widely distributed in the aquatic environments and causing various degrees of aquatic toxicity to aquatic organisms, which has attracted global attention in recent years. Nano-selenium (NSe) has been shown to have the potential to mitigate the harmful impacts of toxic substances. However, there is currently no reported evidence regarding the protective influence of NSe against the adverse effects of MPs. The aim of this study is to determine whether NSe could ameliorate the polystyrene (PS)-MPs-induced injury in grass carp (Ctenopharyngodon idella). The individuals of grass carp were assigned into three groups: (1) the control group fed with basal diet, (2) the PS group fed with basal diet and exposed to PS-MPs, and (3) the NSe group fed with diet supplemented with NSe and exposed to PS-MPs. Our results indicated that NSe administration significantly alleviated the histological damage caused by the PS-MPs in the liver and intestine with lower goblet cell count and larger villus height in the intestine, and significantly lower damage score in the liver. Moreover, NSe mitigated PS-MPs-induced oxidative stress through restoring the activities of antioxidant enzymes (superoxide dismutase (SOD), catalase (CAT), and malondialdehyde (MDA)) except the intestinal CAT activity. Furthermore, NSe supplementation could help fish maintain lower transcriptional level of the immune-related genes (Toll-like receptor 4 (TLR4) and myeloid differentiation factor 88 (MyD88)), inflammation-related genes (major histocompatibility complex class II (MHC-II) and interleukin 8 (IL-8)) and antioxidant enzyme-related genes (nuclear factor (erythroid-derived 2)-like 2 (Nrf-2) and kelch-like ECH-associated protein 1 (Keap-1)) after PS-MPs exposure. Besides, NSe supplementation dramatically helped maintain the intestinal microbial composition, for example, the proportion of Proteobacteria in the grass carp intestine of the NSe group (41 %) was similar to that of the control group (34 %) while 85 % of the PS group. NSe also played a significant protective role in intestinal microbial diversity, effectively resisting the damage on intestinal microbial diversity due to PS-MPs exposure. PS-MPs reduced the beneficial bacteria and increased the pathogenic microorganism like Aeromonas, which was undeniable signs of intestinal dysbiosis. Functional analysis indicated that PS-MPs affected intestinal microbiota functions like inhibition of metabolism, while NSe could significantly alleviate the damage. Our findings suggested that NSe could ameliorate PS-MPs-induced injury, which could contribute to the better understanding of the ecotoxicological effects of MPs on fish and help develop relevant mitigation strategies.

Zhou C ，Wang Z ，Ran M ，Liu Y ，Song Z ... -  《-》

Physiological response and oxidative stress of grass carp (Ctenopharyngodon idellus) under single and combined toxicity of polystyrene microplastics and cadmium.

The harm of microplastics (MPs) to aquatic ecosystems is caused by their stable and non-degradable properties. Additionally, the pollutants such as heavy metals in the water are easy to be adsorbed on their surface with their small particle size and large specific surface area, resulting in environmental pollution. Therefore, the study on the mixture toxicity of MPs and heavy metals has theoretical significance for the risk assessment of aquatic ecosystems. In the present study, 10 nm polystyrene (PS) and cadmium (Cd) were used, and their individual and mixture acute toxicities on grass carp (Ctenopharyngodon idellus) were examined. The results indicated that the mortality of the fish increased with the concentration from 10 mg L-1 to 20 mg L-1, and the existence of PS-MPs elevated the Cd concentrations in the fish and accelerated the death. Whether the Cd and/or the PS-MPs concentrations caused varying degrees of damage to the gills, kidney, liver, and muscles of the grass carp, especially under the highest concentrations (20 mg L-1 Cd + 300 μg L-1 PS-MPs). Moreover, low concentrations of PS-MPs alone (30 μg L-1 PS-MPs) significantly increased the superoxide dismutase (SOD) activity in the kidney and liver, reaching 12.43% and 14.38%, respectively (P < 0.05). The peroxidase (POD) activity was increased only in the kidney, up to 25.95% (P < 0.05). Also, significant reductions in SOD and POD activities were observed in the combination of high concentration of Cd (20 mg L-1) and 300 μg L-1 PS-MPs (P < 0.05). To the best of our knowledge, there are few studies on the impact of combined toxicity of PS-MPs and Cd on grass carp under laboratory conditions. Therefore, these findings may provide a theoretical guarantee for pollution prevention and control in the aquatic ecosystem.

Chen X ，Wang J ，Xie Y ，Ma Y ，Zhang J ，Wei H ，Abdou AIE ... -  《-》

Concurrent impacts of polystyrene nanoplastic exposure and Aeromonas hydrophila infection on oxidative stress, immune response and intestinal microbiota of grass carp (Ctenopharyngodon idella).

Li Z ，Chen F ，Wei M ，Zhi L ，Su Z ，Chong Y ，Xiao Z ，Wang J ... -  《-》

Effects of polystyrene microspheres on the swimming behavior and metabolism of grass carp (Ctenopharyngodon idella).

Microplastics (MPs) are a heterogeneous class of pollutants fouling aquatic environments and they are hazardous to aquatic organisms. This study investigated the size-dependent effects of polystyrene microspheres (PSMPs) on the swimming ability, metabolism, and oxidative stress of juvenile grass carp (Ctenopharyngodon idella). Test fish were exposed to four sizes of PSMPs (0.07, 0.5, 5, and 20-μm), and swimming ability was tested after different exposure times (2, 7, and 15 days). To measure the effect on swimming ability, critical swimming speed (Ucrit) was determined, and to assess metabolic effects, oxygen consumption (MO2), routine metabolic rate (RMR), maximum oxygen consumption (MMR), and excess post-exercise oxygen consumption (EPOC) were determined. To assess the effects on oxidative stress, the activities of two antioxidant enzymes, superoxide dismutase (SOD) and catalase (CAT) were determined in the liver and gills of test fish. After exposure to 20 μm PSMPs, there was a significant drop in Ucrit compared to the control group (P<0.05), with decreases of 22 % on Day 2 and Day 7, and 21 % on Day 15. The RMR and MMR increased significantly (P<0.05), the RMR by 23.9 % on Day 2 and the MMR by 17.2 % on Day 2 and on Day 15, 44.7 % and 20.0 % respectively. The EPOC decreased with exposure time, by 31 % (0.07-μm), 45 %-(0.5-μm), 49 % (5-μm), and 57 % (20-μm) after 15 days. Exposure to the larger PSMPs increased CAT and SOD activity more than the smaller PSMPs and the increases began with SOD activity in the gills. The larger PSMPs were consistently more harmful to juvenile grass carp than the smaller PSMPs. Our results clearly show that PSMPs have detrimental effects on juvenile grass carp and provide additional scientific evidence that environmental monitoring and regulation of microplastic pollution is necessary.

Ali MH ，Huang YP ，Johnson D ，Tu ZY ，Yuan X ... -  《-》