Effects of ocean acidification and polystyrene microplastics on the oysters Crassostrea gigas: An integrated biomarker and metabolomic approach.

The adverse impacts of microplastics (MPs) or ocean acidification (OA) on mollusks have been widely reported, however, little is known about their combined effects on mollusks. The oysters Crassostrea gigas were exposed to two sizes of polystyrene MPs with 1 × 104 particles/L (small polystyrene MPs (SPS-MPs): 6 µm, large polystyrene MPs (LPS-MPs): 50-60 µm) at two pH levels (7.7 and 8.1) for 14 days. The antagonistic effects between MPs and OA on oysters were mainly observed. Single SPS-MPs exposure can induce CAT enzyme activity and LPO level in gills, while LPS-MPs exposure alone can increase PGK and PEPCK gene expression in digestive glands. Ocean acidification can increase clearance rate and inhibit antioxidant enzyme activity, whereas combined exposure of OA and SPS-MPs can affect the metabolomic profile of digestive glands. This study emphasized that the potential toxic effects of MPs under the scene of climate change should be concerned.

Combined effects of salinity and polystyrene microplastics exposure on the Pacific oysters Crassostrea gigas: Oxidative stress and energy metabolism.

Microplastics (MPs) pollution and salinity variation are two environmental stressors, but their combined effects on marine mollusks are rarely known. Oysters (Crassostrea gigas) were exposed to 1 × 104 particles L-1 spherical polystyrene MPs (PS-MPs) of different sizes (small polystyrene MPs (SPS-MPs): 6 µm, large polystyrene MPs (LPS-MPs): 50-60 µm) under three salinity levels (21, 26, and 31 psu) for 14 days. Results demonstrated that low salinity reduced PS-MPs uptake in oysters. Antagonistic interactions between PS-MPs and low salinity mainly occurred, and partial synergistic effects were mainly induced by SPS-MPs. SPS-MPs induced higher lipid peroxidation (LPO) levels than LPS-MPs. In digestive glands, low salinity decreased LPO levels and glycometabolism-related gene expression, which was related to salinity levels. Low salinity instead of MPs mainly affected metabolomics profiles of gills through energy metabolism and osmotic adjustment pathway. In conclusion, oysters can adapt to combined stressors through energy and antioxidative regulation.

Seasonal change of microplastics uptake in the Pacific oysters Crassostrea gigas cultured in the Yellow Sea and Bohai Sea, China.

This study investigated seasonal microplastics (MPs) pollution characteristics in oysters and surrounding surface seawater from five aquaculture farms located at the Yellow Sea and Bohai Sea. MPs abundances in oysters were 2.40 ± 0.14 (winter) to 3.28 ± 0.19 (autumn) items/individual, and 0.22 ± 0.02 (spring) to 0.45 ± 0.06 (summer) items/g (ww). In surface seawater, average seasonal MPs abundances were 3.41 ± 1.06-8.86 ± 2.48 items/L. Fibers were dominant shape, and cellophane and polyethylene terephthalate (PET) were dominant polymers in oysters and surface seawater. Positive correlation was found between oysters' MPs abundance (items/individual) and environmental factors (NO2-N (r = 0.466), and temperature (r = 0.485)) by Spearman correlation analysis in four seasons. Main environmental factor affecting seasonal MPs abundance of oysters and surface seawater was NH3-N and SiO3-Si in summer and winter respectively. In conclusion, seasonal change of MPs uptake in cultured oysters was relatively small.