The accumulation of trace metals in the environmental compartments of coastal rivers is a global and complex environmental issue, requiring multiple tools to constrain the various anthropogenic sources and biogeochemical processes affecting the water quality of these environments. The Valao fluvio-estuarine system (Rio de Janeiro, Brazil) presents a challenging case of a coastal river contaminated by both modern and historical anthropogenic metal sources, located in the land and in the intra-estuary, continuously mixed by tidal cycles. This study employed a combination of spatial distribution analysis of trace metals including gadolinium (Gd), zinc (Zn) isotopic analyses, and X-ray absorption spectroscopy (XAS) to distinguish between these sources. The concentrations of metals in both dissolved (water samples) and surficial sediment compartments (Suspended Particulate Matter and sediment samples) display an overall enrichment trend from upstream to downstream. Multivariate statistical analysis allows to discriminate geogenic elements derived from watershed geology (Ti, K, and Mg) vs anthropogenic contaminants from urban runoff and domestic sewage discharges (Cu, Cr, Pb, Zn, and Gd); and legacy metal contaminants (Zn and Cd) remobilized from ancient metallurgical wastes and transported upstream in the estuary during tidal cycles. The anthropogenic Gd concentration in the dissolved compartment increases along the watercourse, highlighting continuous ongoing sewage discharge. Zinc solid speciation also indicates that Zn contribution from legacy metallurgy waste is primarily associated with sulfide-Zn and Zn-phyllosilicate in the outlet estuary, while in upstream sediments of fluvio-estuarine system, Zn is found bound to organic matter. Zinc isotope systematically reveals a progressive downstream shift to heavier isotope compositions. Upstream, the relatively pristine site and the urbanized section of the river exhibit a relatively uniform δ66/64Zn value (+0.20 ± 0.07 ‰) in suspended particulate matter (SPM) and surficial sediments. These results indicate that domestic sewage discharges contribute to Zn enrichment in sediments of the Valao fluvio-estuarine system but without modifying its isotope signature in sediments. The sediment of the downstream estuarine section shows a heavier δ66/64Zn value (+0.48 ± 0.08 ‰), indicating the strong influence of the intra-estuarine source identified as the historical metallurgic contamination. An integrated view of the geochemical tracers allows thus inferring that the untreated sewage and legacy metallurgical contamination are the primary sources of anthropogenic Zn contamination. It highlights the progressive mixing along the estuarine gradient under tidal dynamics. The influence of the former source continuously expands from the headland towards the estuary.

中文翻译：

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通过结合元素、同位素和物种形成方法，理清城市化沿海河流中过去和现代锌人为来源的贡献


痕量金属在沿海河流环境隔间中的积累是一个全球性的复杂环境问题，需要多种工具来限制影响这些环境水质的各种人为来源和生物地球化学过程。Valao 河流-河口系统（巴西里约热内卢）提出了一个具有挑战性的案例，即一条沿海河流被现代和历史上的人为金属来源污染，位于陆地和河口内，不断受到潮汐循环的混合。本研究结合了痕量金属的空间分布分析，包括钆 （Gd）、锌 （Zn） 同位素分析和 X 射线吸收光谱 （XAS） 来区分这些来源。溶解（水样）和表层沉积物隔室（悬浮颗粒物和沉积物样品）中的金属浓度均显示出从上游到下游的整体富集趋势。多变量统计分析可以区分流域地质产生的地质因素（Ti、K 和 Mg）与城市径流和生活污水排放的人为污染物（Cu、Cr、Pb、Zn 和 Gd）;以及从古代冶金废料中重新移动并在潮汐循环期间输送到河口上游的遗留金属污染物（Zn 和 Cd）。溶解隔室中的人为 Gd 浓度沿河道增加，突出了持续持续的污水排放。锌固体形态还表明，传统冶金废料的 Zn 贡献主要与出口河口的硫化物 Zn 和 Zn-层状硅酸盐有关，而在河流-河口系统的上游沉积物中，Zn 与有机物结合。 锌同位素系统地揭示了向更重同位素组成的下游逐渐转变。上游、相对原始的地点和河流的城市化部分在悬浮颗粒物 （SPM） 和表层沉积物中表现出相对均匀的 δ66/64Zn 值（+0.20 ± 0.07 ‰）。这些结果表明，生活污水排放有助于 Valao 河流-河口系统沉积物中锌的富集，但不会改变其在沉积物中的同位素特征。下游河口剖面的沉积物显示出较重的 δ66/64Zn 值 （+0.48 ± 0.08 ‰），表明河口内来源被确定为历史冶金污染的强烈影响。地球化学示踪剂的综合视图可以推断出未经处理的污水和遗留的冶金污染是人为锌污染的主要来源。它突出了潮汐动力学下沿河口梯度的逐渐混合。前一个源的影响不断从岬角向河口扩大。