Verplanck Philip L, Taylor Howard E, Nordstrom D Kirk, Barber Larry B
U.S. Geological Survey, Box 25046, MS973, Denver, Colorado 80225, USA.
Environ Sci Technol. 2005 Sep 15;39(18):6923-9. doi: 10.1021/es048456u.
In many surface waters, sewage treatment plant (STP) effluent is a substantial source of both regulated and unregulated contaminants, including a suite of complex organic compounds derived from household chemicals, pharmaceuticals, and industrial and medical byproducts. In addition, STP effluents in some urban areas have also been shown to have a positive gadolinium (Gd) anomaly in the rare earth element (REE) pattern, with the Gd derived from its use in medical facilities. REE concentrations are relatively easy to measure compared to many organic wastewater compounds and may provide a more widely utilized tracer of STP effluents. To evaluate whether sewage treatment plant-associated Gd is a useful tracer of treatment plant effluent, an investigation of the occurrence, fate, and transport of rare earth elements was undertaken. The rare earth element patterns of four of five STP effluents sampled display positive Gd anomalies. The one site that did not have a Gd anomaly serves a small community, population 1200, with no medical facilities. Biosolids from a large metropolitan STP are not enriched in Gd even though the effluent is, suggesting that a substantial fraction of Gd remains in the aqueous phase through routine treatment plant operation. To evaluate whether STP-derived Gd persists in the fluvial environment, a 14-km study reach downstream of an STP was sampled. Gadolinium anomalies were present at all five downstream sites, but the magnitude of the anomaly decreased. Effluent from STPs is a complex mixture of organic and inorganic constituents, and to better understand the chemical interactions and their effect on REEs, the aqueous speciation was modeled using comprehensive chemical analyses of water samples collected downstream of STP input. These calculations suggest that the REEs will likely remain dissolved because phosphate and carbonate complexes dominate over free REE ions. This study supports the application of Gd anomalies as a useful tracer of urban wastewater.
在许多地表水中，污水处理厂（STP）排放的废水是受管制和不受管制污染物的重要来源，其中包括一系列源自家用化学品、药品以及工业和医疗副产品的复杂有机化合物。此外，一些城市地区的污水处理厂排放的废水中，稀土元素（REE）模式还显示出正钆（Gd）异常，其中的钆来自医疗设施的使用。与许多有机废水化合物相比，稀土元素浓度相对容易测量，并且可能成为更广泛使用的污水处理厂废水示踪剂。为了评估与污水处理厂相关的钆是否是处理厂废水的有用示踪剂，开展了一项关于稀土元素的发生、归宿和迁移的调查。所采集的五个污水处理厂排放废水中的四个，其稀土元素模式显示出正钆异常。没有钆异常的那个站点服务于一个小社区，人口为1200，且没有医疗设施。尽管污水处理厂排放的废水中钆含量较高，但来自一个大城市污水处理厂的生物固体中钆并未富集，这表明通过污水处理厂的常规运行，相当一部分钆仍留在水相中。为了评估污水处理厂排放的钆在河流环境中是否会持续存在，对一个污水处理厂下游14公里长的研究河段进行了采样。下游的所有五个站点都存在钆异常，但异常程度有所降低。污水处理厂排放的废水是有机和无机成分的复杂混合物，为了更好地理解化学相互作用及其对稀土元素的影响，利用对污水处理厂排放口下游采集的水样进行的综合化学分析，对水相形态进行了建模。这些计算结果表明，稀土元素可能会保持溶解状态，因为磷酸盐和碳酸盐络合物比游离稀土离子占主导地位。这项研究支持将钆异常用作城市废水的有用示踪剂。
