Microplastic Contamination in Pacific Oysters (Crassostrea gigas) from Haizhou Bay: Tissue-Specific Distribution, Digestive Enzyme Dysfunction, and Lipid Metabolism Perturbation

<title>Abstract</title> In this study, we systematically evaluated the distribution characteristics of microplastics in the Pacific oyster (<italic>Crassostrea gigas</italic>) from Haizhou Bay and their effects on digestive enzyme activities and fatty acid metabolism. Through field sampling and laboratory exposure experiments, the abundance of microplastics in the gills, hepatopancreas, and integumentary muscles of the oyster was found to increase linearly with age (R² = 0.112-0.211), with gill tissues accumulating the highest amount. Microplastics in environmental media were dominated by PET, PE, and PVC, which were highly consistent with the contamination profile in oysters, suggesting a direct exposure risk. Laboratory simulations showed that PMMA, PVC, PET and PE microplastics (300, 600, 900 μg/L) significantly inhibited the activities of glutathione reductase (gr), trypsin, lipase and amylase, with a 50% decrease in gr activity in the high concentration group (p &lt; 0.05). Mechanistic analysis showed that microplastics induced oxidative stress through adsorption of pollutants, depletion of reduced glutathione, and physical damage to cells. Fatty acid composition analysis showed that short-term exposure resulted in a significant increase in palmitic acid and arachidonic acid, while DHA and monounsaturated fatty acids significantly decreased, revealing disturbed energy metabolism and impaired membrane function. This study reveals for the first time the dual toxic effects of microplastics on oyster digestive enzymes and fatty acid metabolism, providing a new perspective for marine ecological risk assessment. In the future, it is necessary to combine long-term exposure experiments and histological techniques to further analyze the compound toxicity mechanism of microplastics.