Newton Teresa J, Bartsch Michelle R
U.S. Geological Survey, Upper Midwest Environmental Sciences Center, 2630 Fanta Reed Road, La Crosse, Wisconsin 54603, USA.
Environ Toxicol Chem. 2007 Oct;26(10):2057-65. doi: 10.1897/06-245R.1.
We compared the sensitivity of two juvenile unionid mussels (Lampsilis cardium and Lampsilis higginsii) to ammonia in 96-h water-only and sediment tests by use of mortality and growth measurements. Twenty mussels were placed in chambers buried 2.5 cm into reference sediments to approximate pore-water exposure (sediment tests) or elevated above the bottom of the experimental units (water-only tests). In the sediment tests, a pH gradient existed between the overlying water (mean 8.0), sediment- water interface (mean 7.7), and 2.5 cm depth (mean 7.4). We assumed that mussels were exposed to ammonia in pore water and report effect concentrations in pore water, but if they were exposed to the higher pH water, more of the ammonia would be in the toxic un-ionized (NH(3)) form. The only differences in toxicity and growth between mussel species occurred in some of the water-only tests. In sediment tests, median lethal concentrations (LC50s) ranged from 124 to 125 microg NH(3)-N/L. In water-only tests, LC50s ranged from 157 to 372 microg NH(3)-N/L. In sediment tests, median effective concentrations (EC50s based on growth) ranged from 30 to 32 microg NH(3)-N/L. Juvenile mussels in the water-only tests grew poorly and did not exhibit a dose-response relation. These data demonstrate that growth is a sensitive and valuable endpoint for studies on ammonia toxicity with juvenile freshwater mussels and that growth should be measured via sediment tests.
我们通过死亡率和生长测量，比较了两种幼年珠蚌（心形丽蚌和希金斯丽蚌）在96小时仅水暴露和沉积物试验中对氨的敏感性。将20只蚌放入埋入参考沉积物2.5厘米深处的试验箱中，以模拟孔隙水暴露（沉积物试验），或将其置于实验装置底部上方（仅水暴露试验）。在沉积物试验中，上覆水（平均pH值8.0）、沉积物 - 水界面（平均pH值7.7）和2.5厘米深度处（平均pH值7.4）存在pH梯度。我们假设蚌暴露于孔隙水中的氨，并报告孔隙水中的效应浓度，但如果它们暴露于较高pH值的水中，更多的氨将以有毒的未电离（NH₃）形式存在。蚌类物种之间毒性和生长的唯一差异出现在一些仅水暴露试验中。在沉积物试验中，半数致死浓度（LC50s）范围为124至125微克NH₃ - N/L。在仅水暴露试验中，LC50s范围为157至372微克NH₃ - N/L。在沉积物试验中，半数有效浓度（基于生长的EC50s）范围为30至32微克NH₃ - N/L。仅水暴露试验中的幼年蚌生长不佳，且未表现出剂量 - 反应关系。这些数据表明，生长是研究幼年淡水蚌氨毒性的一个敏感且有价值的终点指标，并且生长应通过沉积物试验来测量。
