De Schamphelaere K A C, Canli M, Van Lierde V, Forrez I, Vanhaecke F, Janssen C R
Laboratory of Environmental Toxicology and Aquatic Ecology, Faculty of Applied Biological Sciences, Ghent University, Jozef Plateaustraat 22, B-9000 Gent, Belgium.
Aquat Toxicol. 2004 Dec 10;70(3):233-44. doi: 10.1016/j.aquatox.2004.09.008.
Regulatory assessments of metals in freshwaters are mostly based on dissolved metal concentrations, assuming that toxicity is caused by waterborne metal only. Little attention has been directed to the toxicity of dietary metals to freshwater invertebrates. In this study the chronic toxicity of dietary zinc to Daphnia magna was investigated. The green alga Pseudokirchneriella subcapitata was exposed for 64 h to a control and three dissolved zinc concentrations, i.e. 23, 28 and 61 microg L(-1), resulting in internal zinc burdens in the algae of 130, 200, 320 and 490 microg g(-1) dry weight, respectively. These algae were used as a food source in chronic, 21-day bioassays with D. magna in a test medium to which no dissolved zinc was added. None of the treatments resulted in effects on feeding rates or somatic growth of D. magna. In contrast, a significant 40% decrease of total reproduction (number of juveniles per adult) was observed in the 28 and 61 microg L(-1) treatments. Time to first brood was not affected, whereas the mean brood size and the fraction of reproducing parent daphnids were reduced from the second brood onwards and the magnitude of these reductions increased with each subsequent brood. The reduced reproduction was accompanied with an elevated zinc accumulation in the 61 microg L(-1) treatment only, suggesting that total body burden is no good indicator of dietary zinc toxicity. Overall our data suggest that dietary zinc specifically targets reproduction in D. magna through accumulation in particular target sites, possibly cells or tissues where vitellogenin synthesis or processing occur. Further, our data illustrate that the potential importance of the dietary exposure route should be carefully considered and interpreted in regulatory assessments of zinc.
对淡水中金属的监管评估大多基于溶解态金属浓度，假定毒性仅由水中的金属引起。很少有人关注膳食金属对淡水无脊椎动物的毒性。在本研究中，调查了膳食锌对大型溞的慢性毒性。将绿藻小形假微型海链藻暴露于对照和三种溶解锌浓度（即23、28和61微克/升）下64小时，导致藻类体内锌含量分别为130、200、320和490微克/克干重。这些藻类被用作大型溞在无添加溶解锌的测试介质中进行21天慢性生物测定的食物来源。没有一种处理对大型溞的摄食率或体细胞生长产生影响。相反，在28和61微克/升处理中，观察到总繁殖量（每只成年个体的幼体数量）显著下降40%。首次产卵时间未受影响，而从第二次产卵开始，平均产卵量和繁殖的亲代大型溞比例降低，且这些降低的幅度随着后续每次产卵而增加。繁殖减少仅在61微克/升处理中伴随着锌积累增加，这表明全身负担不是膳食锌毒性的良好指标。总体而言，我们的数据表明，膳食锌通过在特定靶位点（可能是卵黄蛋白原合成或加工的细胞或组织）积累，特异性地靶向大型溞的繁殖。此外，我们的数据表明，在锌的监管评估中应仔细考虑和解释膳食暴露途径的潜在重要性。
