Bendell Leah I, Feng Cindy
Department of Biological Sciences, Simon Fraser University, 8888 University Avenue Burnaby, BC, Canada V5A 1S6.
Department of Biological Sciences, Simon Fraser University, 8888 University Avenue Burnaby, BC, Canada V5A 1S6.
Mar Pollut Bull. 2009 Aug;58(8):1137-1143. doi: 10.1016/j.marpolbul.2009.04.006. Epub 2009 Apr 29.
Oysters from the north-west coast of Canada contain high levels of cadmium, a toxic metal, in amounts that exceed food safety guidelines for international markets. A first required step to determine the sources of cadmium is to identify possible spatial and temporal trends in the accumulation of cadmium by the oyster. To meet this objective, rather than sample wild and cultured oysters of unknown age and origin, an oyster "grow-out" experiment was initiated. Cultured oyster seed was suspended in the water column up to a depth of 7 m and the oyster seed allowed to mature a period of 3 years until market size. Oysters were sampled bimonthly and at time of sampling, temperature, chlorophyll-a, turbidity and salinity were measured. Oyster total shell length, dry tissue weights, cadmium concentrations (microg g(-1)) and burdens (microg of cadmium oyster(-1)) were determined. Oyster cadmium concentrations and burdens were then interpreted with respect to the spatial and temporal sampling design as well as to the measured physio-chemical and biotic variables. When expressed as a concentration, there was a marked seasonality with concentrations being greater in winter as compared in summer; however no spatial trend was evident. When expressed as a burden which corrects for differences in tissue mass, there was no seasonality, however cadmium oyster burdens increased from south to north. Comparison of cadmium accumulation rates oyster(-1) among sites indicated three locations, Webster Island, on the west side of Vancouver Island, and two within Desolation Sound, Teakerne Arm and Redonda Bay, where point sources of cadmium which are not present at all other sampling locations may be contributing to overall oyster cadmium burdens. Of the four physio-chemical factors measured only temperature and turbidity weakly correlated with tissue cadmium concentrations (r(2)=-0.13; p<0.05). By expressing oyster cadmium both as concentration and burden, regional and temporal patterns were demonstrated, which may have been missed if just concentration was determined.
来自加拿大西北海岸的牡蛎含有高浓度的镉（一种有毒金属），其含量超过了国际市场的食品安全标准。确定镉来源的首要步骤是识别牡蛎积累镉的可能空间和时间趋势。为实现这一目标，开展了一项牡蛎“养成”实验，而非对年龄和来源不明的野生及养殖牡蛎进行采样。养殖的牡蛎苗被悬浮在水深达7米的水柱中，让牡蛎苗成熟3年直至达到上市规格。每两个月对牡蛎进行采样，采样时测量温度、叶绿素a、浊度和盐度。测定牡蛎的总壳长、干组织重量、镉浓度（微克/克⁻¹）和镉含量（微克/牡蛎⁻¹）。然后根据空间和时间采样设计以及所测量的物理化学和生物变量来解释牡蛎的镉浓度和含量。以浓度表示时，存在明显的季节性，冬季浓度高于夏季；然而没有明显的空间趋势。以校正组织质量差异后的含量表示时，没有季节性，但牡蛎的镉含量从南向北增加。各采样点之间牡蛎镉积累速率（牡蛎⁻¹）的比较表明，温哥华岛西侧的韦伯斯特岛以及荒凉海峡内的两个地点（蒂克内湾和雷东达湾），在其他所有采样地点均不存在的镉点源可能导致了牡蛎总体镉含量升高。在所测量的四个物理化学因素中，只有温度和浊度与组织镉浓度存在弱相关性（r² = -0.13；p < 0.05）。通过同时以浓度和含量来表示牡蛎镉，展示了区域和时间模式，如果仅测定浓度，这些模式可能会被遗漏。
