Detection and Depuration of Microplastics in the American Oyster (Crassostrea virginica) Collected from Southern Gulf of Mexico Coast and a Laboratory Study

Microplastics have invaded the aquatic environment and its inhabitants, leading to considerable disturbances. Bivalves are among the main organisms affected by microplastics due to their filter-feeding technique. In this study, approximately 15 oysters were collected from two sites along the Gulf of Mexico coast. We employed a Nile Red staining technique to quantify microplastics in the American oysters (Crassostrea virginica). We compared field samples (collected immediately after harvesting) with laboratory samples (post-depuration study for two weeks) to identify differences in the quantity, shape, and size of microplastics. The field results indicated a significant number of microplastics, with a predominance of microfibers and varying sizes. In contrast, the laboratory results revealed a substantial decrease in both the quantity and size of microplastics, reinforcing the argument for cleaner waters. We performed immunohistochemical analysis to understand the impacts of microplastics on 3-nitrotyrosine protein (NTP) expression in tissues. Our results indicated significantly greater expression of NTP in the field oyster tissues than laboratory oysters, demonstrating how microplastic-infested waters are causing nitrative stress on these organisms, consequently elevating antioxidant enzyme activity. We tested superoxide dismutase and catalase, which exhibited greater expression in the field oysters as they strived to combat the increased stress. Using the Periodic-acid Schiff’s staining technique, we observed less mucus secretion in the field oyster tissues than in the laboratory ones. This strengthens the argument that microplastics are causing heightened stress and leaving oysters vulnerable to other physiological functions. Biochemical analysis was performed to assess oysters’ extrapallial fluid, measuring pH and glucose levels. There were slight significant differences in pH levels between field and laboratory oysters, but no difference in glucose levels. Collectively, this study suggests that microplastics are disrupting and altering the tissue, and therefore, the physiology of oysters.