The pollution of microplastics and polycyclic aromatic hydrocarbons (PAHs) in marine environment is increasingly serious. The toxic effects of polystyrene microplastics and pyrene on the clam Ruditapes philippinarum were investigated in this study. R. philippinarum was exposed to two polystyrene microplastics sizes (0.3 mum and 6 mum, 20 mug/L) and two pyrene concentrations (10 mug/L and 100 mug/L) for 21 days, respectively. For individuals in each treatment, physiological responses (condition index and clearance rate), immune defense and oxidative stress parameters were measured. It was found that except for the pyrene single exposure group, the clearance rate of R. philippinarum in the other exposure groups was significantly lower than that of the control group, but the two pollutants had no significant effect on the condition index of R. philippinarum. Exposure to microplastics and pyrene led to impaired immune function of R. philippinarum, manifested by increased hemocyte apoptosis and inhibited phagocytosis. The apoptosis rate of hemocytes in the exposure group with small size microplastics and high concentration pyrene was significantly higher than that in the control group,and the apoptosis rate of hemocytes in the combined exposure group was the highest. Except for the large size microplastic exposure group,the phagocytic activity of hemocytes in each exposure group was significantly lower than that of the control group. The antioxidant system of R. philippinarum could not remove the free radicals produced in the body in time,leading to oxidative damage in the body,which was manifested as the change of antioxidant enzyme activity and the increase of malonic dialdehyde (MDA) content. The combined exposure of microplastics and pyrene significantly increased the activities of glutathione S-transferase (GST) in gill tissues, and significantly decreased the activities of catalase (CAT) and superoxide dismutase (SOD) in digestive gland tissues. Integrated biomarker response (IBR) analysis showed that the stress caused by combined exposure on R. philippinarum was higher than that of the single exposure group
