Abstract: Cadmium(Cd) is a nonessential element and is potentially highly toxic to human,animal and plant,even at low doses.It accumulates within the bodies of organisms,alters and degrades processes of enzyme activation,causes cell damage and results in organism death.Polycyclic aromatic hydrocarbons(PAHs) are common coastal environmental organic pollutants derived from petroleum,ocean shipping and industry sewage.It is a global problem since these compounds are known to be highly mutagenic and carcinogenic,as well as bioaccumulating and persistent.Heavy met-als and their interactions with PAHs frequently occur,and organisms are usually exposed to chemicals in combinations.The clam Ruditapes philippinarum is a main commercial mollusk widely distribute in the coastal area of China.In the present study,R.philippinarum was exposed to Cd,benzoαpyrene(BaP) and a mixture of Cd and BaP,as model sub-stances,in order to evaluate the relationship of tissue Cd and BaP actuce toxicity,metabolic parameters such as total reduced glutathione(GSH),glutathione S-transferase(GST) and superoxide dismutase(SOD).The aim of the study was to investigate the interference mechanisms between Cd and BaP,as well as assess the parameters for using as biomarkers of the combined pollution in marine environments. Two-year-old calms R.philippinarum,average shell length:(43.5 ± 1.7) mm;shell height:(29.4 ± 1.1) mm;mass:(10.7 ± 1.7) g were collected from the Red Island(Yellow Sea,Qingdao,China).Clams were put in 50 L glass tanks(0.5 L water per clam) and acclimated to photophobic underground laboratory conditions for 10 days in sand-filtered seawater pumped from the Red Island(Yellow Sea,Qingdao,China).The seawater was continuously aerate,and salinity,temperature and pH were maintained at 31 psu,16.0 ± 0.6 °C and 8.1,respectively.The water was renewed every day.The clams were fed with dried powder of Spirulina platensis daily.In the acute experiments,the calms were allocated to three groups with different Cd levels(control,10.0,17.0,28.9,49.13 and 83.521 mg/L),BαP(control,0.625,1.25,2.5,5.0 and 10.0 mg/L) and Cd + BαP(control,10.0+1.0,17.0+1.0,28.9+1.0,49.13+1.and 83.521+1.0 mg/L).The clams were exposed for 96h.The groups of the sub-acute exposure experiment were:(1)15μg Cd/L group,(2)30μg Cd/L group,(3) 0.01 μg/L of BaP group,(4) 0.05 μg/L of BaP group and(5) the mixture of both(15 μg Cd/L + 0.01 μg BaP/L,15 μg Cd/L + 0.05 μg BaP/L,30 μg Cd/L + 0.01 μg BaP/L,30 μg Cd/L + 0.05 μg BaP/L) group and the clams were exposed for 21d. The results showed that the 48,72 and 96h LC50 for Cd2+ to R.philippinarum were 50.41,24.12 and 14.68mg/L,respectively.The joint toxicity of Cd2+ and BαP was synergistic at 48-96h.Cd2+ and BαP only and combined expo-sure had a significant effects on glutathione(GSH) contents,glutathione S-transferase(GST) and superoxide dismutase(SOD) activities of gills and digestive glands of R.philippinarum(P0.05).No significant difference in any of the pa-rameter was observed in the control group.GSH contents of the Cd2+ only or BαP only exposure groups increased and reached the highest value at 1d or 3d,and then decreased.In mixture exposure groups(except Cd + BαP,15μg/L +0.01μg/L),GSH contents were depressed all the time and became stable after 12d.GST and SOD activities showed increasing trend and reached the maximum at 1d or 3d.After 12d GST activities had no significant difference with the control group,but SOD activities were still induced and became stable. In conclusion,Cd2+ and BαP mixture showed significant acute toxic effects on the survival of R.philippinarum.Cd2+ and BαP only and mixture showed linear correlations and time and dose-dependent relationship with GSH con-tents,GST and SOD activities of R.philippinarum.