Ettajani H, Berthet B, Amiard J C, Chevolot L
CNRS, ISOMer, SMAB, Service d'Ecotoxicologie, Nantes, France.
Arch Environ Contam Toxicol. 2001 Feb;40(2):209-21. doi: 10.1007/s002440010165.
Alternative methodologies have been applied to the study of cadmium transfer in a food chain: water, microalgae (Skeletonema costatum and Tetraselmis suecica), oysters (Crassostrea gigas). The potential bioavailability of Cd in organisms was assessed through partitioning at the cell or tissue levels, and the predictive value of this method was evaluated by determining directly the metal transfer in an experimental food chain model. Cd concentrations were lower in S. costatum than T. suecica, in controls as well as in contaminated algae. In both algal species, Cd was firmly bound to the cell wall or had entered the cell. Cytosolic Cd was bound to intracellular ligands, the biochemical characteristics of which were not consistent with the hypothesis of detoxification via phytochelatins. In both algal species, Cd was predominantly present in the insoluble fraction, but at pHs such as those existing in the digestive tract of bivalves, it was easily extracted from the cells. Thus, exposure to Cd through phytoplanktonic food induced a significant uptake of this metal in soft tissues of bivalves. Due to the difference in Cd accumulation in algae, Cd doses associated with S. costatum were lower than those bound to T. suecica. Moreover, oysters retained a lower percentage of the metal associated with S. costatum compared to T. suecica (9 and 20%, respectively, after 21 days of exposure). Cd doses potentially available to oysters exposed directly in sea water were considerably higher, and direct uptake induced the highest levels of Cd incorporation but only 2% of dissolved Cd was actually retained by oysters over 21 days of exposure. In the soft tissues of oysters, Cd was distributed equally between soluble and insoluble fractions. Cytosolic Cd was present predominantly in the heat-stable fraction and mainly bound to compounds of molecular weight equal to 13.5 kDa. Moreover, a positive correlation was observed between metallothionein-like protein (MTLP) levels and gross concentrations of Cd in the soft tissues of oysters. These data are consistent with the hypothesis of an important role of metallothioneins in Cd metabolism in oysters and suggest a potential availability of MT-bound fraction of Cd to the consumers. These data are in agreement with the response of oysters exposed to Cd in the field.
水、微藻（中肋骨条藻和瑞典四爿藻）、牡蛎（太平洋牡蛎）。通过细胞或组织水平的分配评估生物体中镉的潜在生物有效性，并通过在实验食物链模型中直接测定金属转移来评估该方法的预测价值。在对照以及受污染的藻类中，中肋骨条藻中的镉浓度低于瑞典四爿藻。在这两种藻类中，镉要么牢固地结合在细胞壁上，要么已进入细胞。胞质镉与细胞内配体结合，其生化特性与通过植物螯合肽解毒的假设不一致。在这两种藻类中，镉主要存在于不溶性部分，但在双壳贝类消化道中存在的pH值条件下，它很容易从细胞中提取出来。因此，通过浮游植物性食物接触镉会导致双壳贝类软组织中大量吸收这种金属。由于藻类中镉积累的差异，与中肋骨条藻相关的镉剂量低于与瑞典四爿藻结合的镉剂量。此外，与瑞典四爿藻相比，牡蛎对与中肋骨条藻相关的金属的保留百分比更低（暴露21天后分别为9%和20%）。直接暴露于海水中的牡蛎可获得的镉剂量要高得多，直接吸收导致镉掺入水平最高，但在21天的暴露期间，实际上只有2%的溶解镉被牡蛎保留。在牡蛎的软组织中，镉在可溶性和不溶性部分中分布均匀。胞质镉主要存在于热稳定部分，主要与分子量等于13.5 kDa的化合物结合。此外，在牡蛎软组织中，金属硫蛋白样蛋白（MTLP）水平与镉的总浓度之间观察到正相关。这些数据与金属硫蛋白在牡蛎镉代谢中起重要作用的假设一致，并表明镉与MT结合部分对消费者具有潜在的可利用性。这些数据与野外暴露于镉的牡蛎的反应一致。
