Synergistic Toxicity of PVC Microplastic and Methyl Thiophanate in Common Carp

Little is known about how microplastics (MPs) interact with other environmental pollutants. In light of this, the present work investigated the individual and combined toxicity of polyvinyl chloride (PVC) MPs and the fungicide methyl thiophanate (MT) in common carp. A total of 90 fish were randomly assigned to nine experimental groups. Following a 28-day exposure period, hematological indices, antioxidant responses, serum biochemical parameters, and tissue alterations were evaluated to determine the biological effects of PVC and MT, both separately and in combination. The data were analyzed using the ANOVA test at a significance level of p < 0.05. Red blood cell counts (RBCs, millions/mm³) declined noticeably in all treated groups compared with the control fish. Values recorded for Groups F, G, H, and I were 1.83 ± 0.14, 1.77 ± 0.21, 1.41 ± 0.17, and 1.37 ± 0.12, respectively, whereas the control group showed a value of 2.37 ± 0.21. Groups B, C, D, and E also had a decrease compared to the control group, but it was not significant. A similar pattern appeared for superoxide dismutase activity (SOD, ꓴ/mL), an important antioxidant defense enzyme. Enzyme activity in Groups F-I ranged from 101.14 ± 9.10 to 113.13 ± 13.56, considerably lower than the control level of 129.61 ± 19.44. Biochemical disturbances were also evident. Serum triglyceride concentrations remained altered in exposed fish, with measured values of 73.48 ± 10.28, 69.58 ± 11.52, 61.82 ± 8.03, and 54.37 ± 8.15 mg/dL for Groups F-I, compared with 83.01 ± 9.13 mg/dL in the control group. In addition, alkaline phosphatase (ALP) activity increased significantly (p < 0.05) across all experimental groups relative to untreated fish, suggesting physiological stress and possible tissue dysfunction. Histopathological observations added another layer to these findings. Fish exposed simultaneously to PVC MPs and MT exhibited more severe damage in the gill and intestinal tissues than fish subjected to either contaminant alone, and the extent of injury became more pronounced as exposure concentrations increased. In other words, the combined presence of MPs and chemical pollutants may produce stronger toxic effects than would be expected from single-compound exposure. The data also reinforce the need for more careful environmental monitoring, especially in waters receiving mixtures of plastic debris and agrochemical contaminants.