Kuhn Isadora Aumond, Roisenberg Ari
Brazilian Geological Survey, Brazil.
Federal University of Rio Grande do Sul, Brazil.
J Environ Radioact. 2017 Oct;177:24-31. doi: 10.1016/j.jenvrad.2017.05.013. Epub 2017 May 31.
The Rio dos Sinos Watershed area is located at the Middle-West region of the Rio Grande do Sul State, Southern Brazil, along thirty two municipalities and affecting 1.5 million inhabitants and many important industrial centers. Three main aquifers are recognized in the study area: the unconfined-fractured Serra Geral Aquifer System, the porous Guarani Aquifer System, and the Permian Aquitard. This study aims to understand groundwater, surface water and human activity interactions in the Rio dos Sinos Watershed, evaluating the application of stable lead isotopic ratios analyzed for this propose. Thirty six groundwater samples, 8 surface water samples and 5 liquid effluents of tanneries and landfills samples were measured using a Thermal Ionization Mass Spectrometer Thermo-Finnigan and a Neptune Multi-Collector Inductively Coupled Plasma Mass Spectrometer. Groundwater isotopic ratios have a wider range compared to the surface water, with less radiogenic averages Pb/Pb = 38.1837 vs 38.4050 (standard deviation = 0.2921 vs 0.1343) and Pb/Pb = 18.2947 vs 18.4766 (standard deviation = 0.2215 vs 0.1059), respectively. Industrial liquid effluents (tanneries and industrial landfill) have averages Pb/Pb = 38.1956 and Pb/Pb = 18.3169, distinct from effluent samples of domestic sanitary landfill (averages Pb/Pb = 38.2353 and Pb/Pb = 18.6607). Hierarchical cluster analysis led to distinguish six groups of groundwater, representing the three aquifers that occur in the area, two clusters suggesting groundwater mixtures and one demonstrating a highly contaminated groundwater. By analyzing the cluster results and wells' stratigraphic profiles it was possible to distinguish the different aquifers in the area. The Serra Geral Aquifer System has Pb/Pb ratios between 18.4718 and 18.7089; Pb/Pb between 15.6692 and 15.6777; Pb/Pb between 38.6826 and 38.7616; Pb/Pb between 0.8372 and 0.8623; Pb/Pb between 2.0671 and 2.0964 and the Guarani Aquifer System has a wider range (Pb/Pb ranged from 37.9393 to 38.1279 and Pb/Pb ranged from 18.0892 to 18.3217). Water mixing of these two aquifer systems is reflected by transitional results. The results confirm that the hierarchical cluster analysis of lead isotopes is a useful tool to discriminate different aquifer conditions, reflecting mostly the influence of the natural lead isotopic composition of the aquifers instead of the anthropogenic activities (urban and industrial), except when the groundwater is highly contaminated by human activity.
西诺斯河流域位于巴西南部南里奥格兰德州的中西部地区，涵盖32个市镇，影响着150万居民以及众多重要的工业中心。研究区域内识别出三个主要含水层：非承压裂隙热拉尔含水层系统、多孔瓜拉尼含水层系统以及二叠纪弱透水层。本研究旨在了解西诺斯河流域地下水、地表水与人类活动之间的相互作用，评估为此目的而分析的稳定铅同位素比值的应用。使用热电离质谱仪Thermo - Finnigan和海王星多接收电感耦合等离子体质谱仪对36个地下水样本、8个地表水样本以及5个制革厂和垃圾填埋场的液体废水样本进行了测量。与地表水相比，地下水同位素比值范围更广，放射性较低的平均值分别为Pb/Pb = 38.1837对比38.4050（标准差 = 0.2921对比(0.1343)）以及Pb/Pb = 18.2947对比18.4766（标准差 = 0.2215对比(0.1059)）。工业液体废水（制革厂和工业垃圾填埋场）的平均值为Pb/Pb = 38.1956和Pb/Pb = 18.3169，与生活卫生垃圾填埋场的废水样本（平均值为Pb/Pb = 38.2353和Pb/Pb = 18.6607）不同。层次聚类分析区分出六组地下水，代表该地区存在的三个含水层，两组表明地下水混合，一组显示出高度污染的地下水。通过分析聚类结果和水井的地层剖面，可以区分该地区不同的含水层。热拉尔含水层系统的Pb/Pb比值在18.4718至18.7089之间；Pb/Pb在15.6692至15.6777之间；Pb/Pb在38.6826至38.7616之间；Pb/Pb在0.8372至0.8623之间；Pb/Pb在2.0671至2.0964之间，瓜拉尼含水层系统的范围更广（Pb/Pb范围从37.9393至38.1279，Pb/Pb范围从18.0892至18.3217）。这两个含水层系统的水混合情况通过过渡性结果得以体现。结果证实，铅同位素的层次聚类分析是区分不同含水层条件的有用工具，主要反映了含水层天然铅同位素组成的影响，而非人为活动（城市和工业）的影响，除非地下水受到人类活动的高度污染。
