Eckley Chris S, Eagles-Smith Collin, Luxton Todd P, Hoffman Joel, Janssen Sarah
U.S. EPA, Region 10, Seattle, WA, United States.
U.S. Geological Survey, Forest and Rangeland Ecosystem Science Center, Corvallis, OR, United States.
Front Environ Chem. 2023;4:1096199. doi: 10.3389/fenvc.2023.1096199. Epub 2023 Feb 9.
Ecosystems downstream of mercury (Hg) contaminated sites can be impacted by both localized releases as well as Hg deposited to the watershed from atmospheric transport. Identifying the source of Hg in water, sediment, and fish downstream of contaminated sites is important for determining the effectiveness of source-control remediation actions. This study uses measurements of Hg stable isotopes in soil, sediment, water, and fish to differentiate between Hg from an abandoned Hg mine from non-mine-related sources. The study site is located within the Willamette River watershed (Oregon, United States), which includes free-flowing river segments and a reservoir downstream of the mine. The concentrations of total-Hg (THg) in the reservoir fish were 4-fold higher than those further downstream (>90 km) from the mine site in free-flowing sections of the river. Mercury stable isotope fractionation analysis showed that the mine tailings (δHg: -0.36‰ ± 0.03‰) had a distinctive isotopic composition compared to background soils (δHg: -2.30‰ ± 0.25‰). Similar differences in isotopic composition were observed between stream water that flowed through the tailings (particulate bound δHg: -0.58‰; dissolved: -0.91‰) versus a background stream (particle-bound δHg: -2.36‰; dissolved: -2.09‰). Within the reservoir sediment, the Hg isotopic composition indicated that the proportion of the Hg related to mine-release increased with THg concentrations. However, in the fish samples the opposite trend was observed-the degree of mine-related Hg was lower in fish with the higher THg concentrations. While sediment concentrations clearly show the influence of the mine, the relationship in fish is more complicated due to differences in methylmercury (MeHg) formation and the foraging behavior of different fish species. The fish tissue δC and ΔHg values indicate that there is a higher influence of mine-sourced Hg in fish feeding in a more sediment-based food web and less so in planktonic and littoral-based food webs. Identifying the relative proportion of Hg from local contaminated site can help inform remediation decisions, especially when the relationship between total Hg concentrations and sources do not show similar covariation between abiotic and biotic media.
汞（Hg）污染场地下游的生态系统可能会受到局部汞释放以及大气传输沉降至流域的汞的影响。确定污染场地下游水体、沉积物和鱼类中汞的来源，对于评估源头控制修复行动的有效性至关重要。本研究利用土壤、沉积物、水和鱼类中汞稳定同位素的测量结果，区分废弃汞矿中的汞与非矿山相关来源的汞。研究地点位于美国俄勒冈州的威拉米特河流域，该流域包括河流的自由流动段和矿山下游的一座水库。水库鱼类中的总汞（THg）浓度比矿山下游90多公里处河流自由流动段的鱼类高出4倍。汞稳定同位素分馏分析表明，与背景土壤（δHg：-2.30‰±0.25‰）相比，矿尾矿（δHg：-0.36‰±0.03‰）具有独特的同位素组成。流经尾矿的溪流水（颗粒态结合δHg：-0.58‰；溶解态：-0.91‰）与背景溪流（颗粒态结合δHg：-2.36‰；溶解态：-2.09‰）之间也观察到类似的同位素组成差异。在水库沉积物中，汞同位素组成表明，与矿山释放相关的汞的比例随总汞浓度增加而增加。然而，在鱼类样本中观察到相反的趋势——总汞浓度较高的鱼类中，与矿山相关的汞的比例较低。虽然沉积物浓度清楚地显示了矿山的影响，但由于甲基汞（MeHg）形成的差异和不同鱼类的觅食行为，鱼类中的关系更为复杂。鱼类组织的δC和ΔHg值表明，在以沉积物为基础的食物网中觅食的鱼类受矿山来源汞的影响更大，而在以浮游生物和沿岸生物为基础的食物网中觅食的鱼类受影响较小。确定来自当地污染场地的汞的相对比例有助于指导修复决策，特别是当总汞浓度与来源之间的关系在非生物和生物介质之间没有显示出类似的协变关系时。
