Ball Angela L, Borgmann Uwe, Dixon D George
Department of Biology, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada.
Environ Toxicol Chem. 2006 Sep;25(9):2526-32. doi: 10.1897/05-650r.1.
Four- and 10-week chronic toxicity tests were conducted using the freshwater amphipod Hyalella azteca and Cd-contaminated Chlorella sp. as a food source. Chlorella sp. was cultured in various Cd concentrations, filtered from solution, rinsed, dried, and ground into food flakes for the H. azteca. Unlike Cd toxicity from water sources, growth was found to be a more sensitive toxicological endpoint than survival, with calculated 50 and 25% effect concentrations (EC50s and EC25s, respectively) of 5.43 and 2.82 nmol/g, respectively, for Cd measured in food. Based on the regression of Cd in Chlorella sp. against Cd in filtered culture medium, the EC50 and EC25 corresponded to dissolved Cd concentrations of 11.30 and 5.09 nmol/L, respectively. Little or no bioaccumulation of Cd was found in the tissues of H. azteca that were fed contaminated food. These results demonstrate an apparent toxicological effect (either direct or indirect) of Cd-contaminated Chlorella sp. to H. azteca that is not associated with Cd accumulation. Toxicity of Cd-contaminated Chlorella sp. differs from waterborne Cd toxicity both in terms of the most sensitive endpoint (growth vs survival) and the relationship between toxicity and bioaccumulation. Unlike Cd toxicity through water exposure, Cd bioaccumulation by H. azteca cannot, therefore, be used to infer toxicity of Cd in a diet of Chlorella sp. Although the concentration of Cd in the algal culture medium that ultimately reduced growth of H. azteca in the present study was higher than Cd in water, which caused mortality to H. azteca in water-only tests during previous studies, further research regarding the contribution of dietary Cd to overall Cd toxicity is needed to verify that water-quality guidelines and risk assessments based on water-only exposures are fully protective.
使用淡水双足类动物墨西哥裸腹溞和受镉污染的小球藻作为食物来源进行了为期4周和10周的慢性毒性试验。小球藻在不同镉浓度下培养，从溶液中过滤、冲洗、干燥并研磨成墨西哥裸腹溞的食物薄片。与水源中的镉毒性不同，生长被发现是比生存更敏感的毒理学终点，食物中镉的计算50%和25%效应浓度（分别为EC50和EC25）分别为5.43和2.82 nmol/g。根据小球藻中镉与过滤后培养基中镉的回归关系，EC50和EC25分别对应于溶解镉浓度11.30和5.09 nmol/L。在喂食受污染食物的墨西哥裸腹溞组织中几乎没有发现镉的生物积累。这些结果表明，受镉污染的小球藻对墨西哥裸腹溞有明显的毒理学效应（直接或间接），且与镉积累无关。受镉污染的小球藻的毒性在最敏感终点（生长与生存）以及毒性与生物积累的关系方面与水体镉毒性不同。因此，与通过水暴露的镉毒性不同，墨西哥裸腹溞对镉的生物积累不能用于推断小球藻饮食中镉的毒性。尽管在本研究中最终降低墨西哥裸腹溞生长的藻类培养基中镉的浓度高于水中的镉浓度，而在先前的仅水测试中水中的镉导致墨西哥裸腹溞死亡，但仍需要进一步研究饮食镉对总体镉毒性的贡献，以验证基于仅水暴露的水质指南和风险评估是否具有充分的保护作用。
