Differential biochemical responses of Cyprinus carpio after dietary and waterborne exposure to microplastics from polyethylene-based biodegradable and conventional bags.

Microplastics (MPs) can interact and generate toxic effects on exposed organisms, such as fish. However, little is known about the effects of exposing fish to biodegradable PE-MPs, and how the form of exposure is related to toxicity. The current study aimed to evaluate the impact of dietary and waterborne exposure to four types of polyethylene MPs (PE-MPs) from biodegradable and conventional bags on common carp Cyprinus carpio. The toxicity of PE-MPs from biodegradable (PE-BIO), transparent (HDPE-1), black (PE-OXO), and gray (HDPE-2) bags was analyzed after 7 days of exposure by multiple biochemical biomarkers assessment, such as neurotoxicity, oxidative and nitrosative stress, and oxidative damage. The toxicity of waterborne exposure of fish to PE-MPs followed the order: PE-OXO>HDPE-2>PE-BIO>HDPE-1, while the dietary exposure was: HDPE-2>PE-BIO>HDPE-1>PE-OXO. Furthermore, according to IBRv2, the HDPE-2 and PE-BIO treatments of dietary exposure showed greater changes in biomarkers compared to the control. Lipid peroxidation levels were altered only in dietary exposure treatments, while CAT and GST activity was generally inhibited in both exposure pathways. The PE-BIO treatments showed significant differences in relation to conventional plastics, mainly in the nitric oxide (NO) content of the fish liver, which increased or decreased depending on the route of exposure. Therefore, this pioneering study emphasizes that the composition of PE-MPs and the route of exposure can generate different effects on C. carpio biomarkers. Furthermore, these results may indicate the effects of environmental contamination by MPs in a freshwater fish species.