Some Physiological, Histopathological, and Molecular Alterations in Common Carp (Cyprinus carpio L.) Exposed to Polystyrene Microplastics

• Saeb Zahim Abbas

  Author

Background :Polystyrene microparticles (PS-MPs) are becoming more accepted as deleterious to freshwater ecosystems.  However, there are not many ecotoxicological studies that have correlated pollutant concentration in the field with the fish species in the river systems of the Middle East. The aim of the study was to evaluate the physiological as well as the histopathological and molecular aspects of the impact of chronic exposure to ecologically relevant concentrations of PS-MPs on juvenile common carp of the Tigris River.

Materials and Methods : Juvenile common carp (Cyprinus carpio; average weight 14.8 1.9 g) were used for studying the chronic effects of PS-MPs via laboratory studies for 60 days using commercially available standardized spherical PS-MPs (Sigma Aldrich No. 43302) with dimensions ranging between 1 and 10 µm. Four concentrations were used that were 0, 0.01, 1, and 1 mg/L which were developed based on the field concentrations provided for the Tigris River at the Samarra site (median values of 0.14 ± 0.09 mg/L and 95th percentile values of 0.78 mg/L). Effects were evaluated through measurement of blood count and serum biochemistry (biomarkers of oxidative stress including malondialdehyde [MDA], superoxide dismutase [SOD], catalase [CAT], and glutathione peroxidase [GPx]), histopathological evaluations of gill and liver with semi-quantitative method of HAI (based on Bernet method) and expression analysis of genes of interest (il-1β, tnf-α, sod, and cat) through RT-qPCR technique.

Results One hundred percent survival was recorded by each group and important effects were only noted in the 1 mg/L group [MF13.1]: there was a reduction in specific growth rate (14.3%, P < 0.01), there was a decline in RBC count and haemoglobin levels (P < 0.05), serum ALT level was increased (from 18.3 ± 1.4 to 31.6 ± 2.3 U/L, P < 0.001), and hepatic MDA was at elevated levels (1.74 times higher at P < 0.01). There were no important changes recorded for the control group and groups exposed to low and medium concentrations. HAI scores were higher in both liver and gill tissues as concentration increased (Kruskal-Wallis test P < 0.001). At a transcriptional level, il-1β and tnf-α were up-regulated by 2.27 and 1.84 times respectively, while sod and cat genes were down-regulated, by 0.71 and 0.74 times (but only with reference to the high concentration).

Conclusions: The findings demonstrate that PS-MPs at chronic environmentally relevant concentrations have damaging effects on the physiology of juvenile common carp. Thus, testing juvenile common carp, a species that is both economically and ecologically important in the Middle East, provides an appropriate model.

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