文蛤谷胱甘肽抗氧化系统对北部湾沉积物中可提取态重金属的响应

为识别海洋双壳类谷胱甘肽抗氧化系统对滨海沉积物重金属可提取态和总量的响应特征差异,分析了北部湾潮间带沉积物中不同形态Cu、Pb、Zn、Cd、Cr的质量分数,文蛤(Meretrix meretrix)鳃组织中w(GSH)(GSH为还原型谷胱甘肽)、w(GSSG)(GSSG为氧化型谷胱甘肽)、GPx(谷胱甘肽过氧化物酶)和GST(谷胱甘肽硫转移酶)活性,并计算w(GSH)/w(GSSG)、tGSH(总谷胱甘肽)含量和OSI(氧化逆境指数). 结果表明:w(TE-Pb)(TE-Pb为可提取态Pb,下同)、w(TE-Cr)、w(TE-Cu)、w(TE-Zn)和w(TE-Cd)平均值分别为13.40、1.93、13.19、30.09和0.10mg/kg; w(TE-Cd)占w(T-Cd)(T-Cd为总Cd,下同)的60.2%~98.1%,并且主要为弱酸溶解态和有机物及硫化物结合态；部分采样点w(TE-Pb)和w(TE-Zn)较高,二者占w(T-Pb)和w(T-Zn)的平均值分别为44.6%和56.6%；Cr、Cu分别在全部或大多数采样点以残渣态为主,可提取态含量平均仅占总量的17.9%和36.5%. 重金属的可提取态质量分数与总量的空间分布基本一致(Cr除外). 文蛤鳃中w(GSH)、w(GSSG)分别为4.07~6.06、4.01~6.59mg/g. 抗氧化指标对沉积物中重金属总量和可提取态质量分数均有显著响应的为w(GSSG)与Cd,w(GSH)/w(GSSG)与Cr和Cd,OSI与Cr和Cd. 然而,w(GSH)/w(GSSG)和OSI只对w(T-Zn)有良好响应；GST只与w(TE-Cu)、w(TE-Zn)显著相关. 某些抗氧化指标对重金属总量和可提取态质量分数表现出不同程度的响应,因此,不能单独依据双壳类对重金属总量的生化响应特征来筛选用于沉积物综合毒性评价的生物标志物. 

Response of Glutathione Antioxidant System in Bivalve Meretrix meretrix to Speciation and Content of Heavy Metals in Coastal Sediments in Beibu Bay, China

The aims of this study were to identify the differences of glutathione antioxidant system responses in marine bivalves to the extractable and total contents of heavy metals in costal sediments, and to provide the information for screening suitable biomarkers reflecting the comprehensive toxicity of heavy metals. The speciation of Cu, Pb, Zn, Cd and Cr were measured in intertidal sediments from different sites along the Beibu Bay. In addition, w(GSH) (reduced glutathione content), w(GSSG) (oxidized glutathione content), GPx (glutathione peroxidase) activity, GST (glutathione S-transferase) activity,tGSH (total glutathione content), w(GSH)/w(GSSG) and OSI (oxidative stress index) in gills of Meretrix meretrix were determined or calculated. Results showed that the mean values were 13.40,1.93,3.19,0.09and 0.10mg/kg for w(TE-Pb) (extractable Pb), w(TE-Cr), w(TE-Cu), w(TE-Zn), w(TE-Cd), respectively. w(TE-Cd) accounted for 60.2%-98.1% of w(T-Cd) (total Cd), which was notably higher than its residual fraction, and composed mainly of water/acid soluble fraction and organic matter/sulphides fraction; higher percentages of w(TE-Pb) and w(TE-Zn) were observed at some sampling sites, on average accounted for 44.6% and 56.6% of the total contents; Cr and Cu were dominated by the residual fraction, the extractable forms counted for only 17.9% and 36.5% of the total on average. The spatial variation of extractable contents were consistent with that of the total contents for most of the metals except Cr. w(GSH) and w(GSSG) were 4.07-6.06,4.01-6.59mg/g respectively. The antioxidant factors significantly responded to both total contents and extractable contents of metals included w(GSSG) versus Cd, w(GSH)/w(GSSG) versus Cr and Cd, OSI versus Cr and Cd. However, w(GSH)/w(GSSG) and OSI were only affected by w(T-Zn), and GST activity was associated only with w(TE-Cu) and w(TE-Zn). There were significant differences in the responses of some antioxidant factors to total and extractable heavy metals. The results confirm that biomarkers for integrated sediment toxicity assessment can not be solely decided on the basis of the total content of heavy metals in the sediment.