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 metals 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, benzo[α]pyrene (BaP) and a mixture of Cd and BaP, as model substances, 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 ℃ 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), B[α]P (control, 0.625, 1.25, 2.5, 5.0 and 10.0 mg/L) and Cd + B[α]P (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 B[α]P was synergistic at 48-96h.Cd2+ and B[α]P only and combined exposure 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 (P＜0.05).No significant difference in any of the parameter was observed in the control group.GSH contents of the Cd2+ only or B[α]P only exposure groups increased and reached the highest value at Id or 3d, and then decreased.In mixture exposure groups (except Cd + B[α]P ,15μg/L +0.01tg/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 ld 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 B[α]P mixture showed significant acute toxic effects on the survival of R.philippinarum.Cd2+ and B[α]P only and mixture showed linear correlations and time and dose-dependent relationship with GSH contents, GST and SOD activities of R.philippinarum.%文章研究了Cd2+-B[α]P复合污染对菲律宾蛤仔的急性毒性和鳃丝、消化盲囊解毒代谢酶活力的影响.结果表明:Cd2+对菲律宾蛤仔48、72、96h LC50分别为50.41、24.12、14.68 mg/L,Cd2+-B[α]P对菲律宾蛤仔的联合急性毒性48-96h表现为协同作用.Cd2+、B[α]P单一与复合污染对菲律宾蛤仔鳃丝、消化盲囊谷胱甘肽(GSH)含量、谷胱甘肽硫转移酶(GST)和超氧化物歧化酶(SOD)活力的影响显著(P＜0.05),而对照组无显著变化.单一染毒组组织GSH含最在12d内呈峰值变化,分别于1d、3d达到最大值,12d后保持稳定,表现为恢复至对照组水平或被诱导;复合污染处理组组织GSH含量除Cd2++B[α]P(15 μg/L+0.01 μg/L)处理组在3d内呈峰值变化外,其他处理组均呈逐渐下降趋势,均于12d后稳定,被显著抑制.各染毒处理组组织GST、SOD活力在12d内呈峰值变化,分别于1d、3d达到最大值,12d后各处理组GST、SOD活力趋于稳定,GST活力与对照组无明显差异,而SOD活力明显高于对照组水平.由此可见,菲律宾蛤仔在Cd2+-B[α ]P复合胁迫下急性毒性效应明显,组织解毒代谢酶活力表现出明显的时间、剂量效应性,鳃丝、消化盲囊GSH含量和SOD活力可作为菲律宾蛤仔Cd2+-B[α]P复合污染评价的潜在生物标志物.
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