Bielmyer Gretchen K, Grosell Martin, Paquin Paul R, Mathews Rooni, Wu Kuen B, Santore Robert C, Brix Kevin V
University of North Florida, Jacksonville, Florida 32256, USA.
Environ Toxicol Chem. 2007 Oct;26(10):2241-6. doi: 10.1897/06-634R.1.
An important final step in development of an acute biotic ligand model for silver is to validate predictive capabilities of the biotic ligand model developed for fish and invertebrates. To accomplish this, eight natural waters, collected from across North America, were characterized with respect to ionic composition, pH, dissolved organic carbon, and sulfide. Tests were conducted with the cladoceran Ceriodaphnia dubia (48-h static) and the fish Pimephales promelas (96-h static renewal) to determine the concentrations causing lethality to 50% of the organisms (LC50s) for silver in each of these waters. Overall, the biotic ligand model adequately predicted silver toxicity to C. dubia; however, in some cases, predicted LC50 values exceeded measured values. The accuracy of the biotic ligand model predictions was less convincing for silver toxicity to P. promelas with pronounced problems in low-ionic strength waters. Another issue was the use of acclimated organisms in toxicity studies because the biotic ligand model has been developed with the use of a mix of studies with acclimated and nonacclimated test organisms of varying ages and sizes. To evaluate whether effects of acclimation to test waters influence biotic ligand model predictions, a subset of the natural waters were also tested with P. promelas that had been acclimated to the natural water for 7 d before testing. These experiments revealed no differences in toxicity between acclimated and nonacclimated P. promelas. To determine the influence of organism size, which has been previously correlated to Na(+) turnover and acute silver toxicity across multiple species, Na(+) and Cl(-) influx rates were measured in P. promelas of different sizes. Our results show that Na(+) and Cl(-) influx rates were inversely related to fish mass and positively correlated with silver sensitivity.
开发银的急性生物配体模型的最后一个重要步骤是验证为鱼类和无脊椎动物开发的生物配体模型的预测能力。为实现这一目标，从北美各地采集了8种天然水体，对其离子组成、pH值、溶解有机碳和硫化物进行了表征。使用枝角类的杜氏宽水蚤（48小时静态试验）和鱼类黑头软口鲦（96小时静态更新试验）进行测试，以确定这些水体中银对50%的生物体造成致死的浓度（半数致死浓度LC50）。总体而言，生物配体模型充分预测了银对杜氏宽水蚤的毒性；然而，在某些情况下，预测的LC50值超过了实测值。生物配体模型对银对黑头软口鲦毒性的预测准确性不太令人信服，在低离子强度水体中存在明显问题。另一个问题是在毒性研究中使用了驯化的生物体，因为生物配体模型是通过使用不同年龄和大小的驯化和未驯化试验生物体的混合研究而开发的。为了评估适应试验水体的影响是否会影响生物配体模型的预测，还使用在测试前已在天然水中适应7天的黑头软口鲦对一部分天然水体进行了测试。这些实验表明，驯化和未驯化的黑头软口鲦在毒性方面没有差异。为了确定生物体大小的影响，此前已发现其与多种物种的Na(+)周转率和急性银毒性相关，对不同大小的黑头软口鲦测量了Na(+)和Cl(-)的流入速率。我们的结果表明，Na(+)和Cl(-)的流入速率与鱼的体重呈负相关，与银敏感性呈正相关。
