Exposure to polypropylene microplastics via diet and water induces oxidative stress in Cyprinus carpio

•Toxicity of polypropylene (PP) microplastic was tested in Cyprinus carpio.•Although there were no deaths, PP microplastics caused oxidative damage to carp gills.•PP microplastics influenced the CAT, MDA, GSH, and TPC levels in carp gill tissues.•Carp were more affected by microplastics from exposure via diet than from exposure to water. The occurrence of accumulation of microplastics in humans and wildlife has become a serious concern on a global scale, especially in the last decade. Although there are many studies on microplastics, their biological effects and toxicity on freshwater fish have not been fully revealed. In order to evaluate the potential toxic effects of PP (polypropylene) microplastics in freshwater fish, we performed 1-day, 2-day, 3-day, 4-day, 5-day, 6-day, and 7-day microplastic exposure to different concentrations of the microplastics through water and diet on Cyprinus carpio. Fish samples were divided into 3 groups; Group-A with different PP microplastic concentrations in their water (ALow:1.0 g/L and AHigh:2.5 g/L), Group-B with different PP microplastic concentrations in their diet (BLow:100 mg/g and BHigh:250 mg/g), and Group-C (Control group) free of PP microplastics in their diet and water. The results showed that although microplastics did not cause death in C. carpio, they caused oxidative stress in comparing the MP exposed groups to the control groups. When indices of oxidative stress of fish individuals in all treatment groups were compared with the control group, it was determined that MDA (malondialdehyde) and GSH (glutathione) levels increased, while TPC (total protein content) and CAT (catalase) levels decreased depending on the concentrations and exposure times. Significant differences were observed between the control and treatment groups in the indices of oxidative stress (P