Article pubs.acs.org/est
Origin and Dynamics of Rare Earth Elements during Flood Events in Contaminated River Basins: Sr−Nd−Pb Isotopic Evidence Christophe Hissler,*,† Peter Stille,‡ Jean François Iffly,† Cédric Guignard,† François Chabaux,‡ and Laurent Pfister† †
CAT/WATER/ERIN/LIST, 41 rue du Brill, 4422 Belvaux, Luxembourg LHyGeS - UMR 7517 CNRS - EOST/UdS, 1 rue Blessig, 67084 Strasbourg Cedex, France
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S Supporting Information *
ABSTRACT: In order to precisely quantify the contribution of anthropogenic activities and geogenic sources to the dissolved and suspended loads of rivers we have combined for the first time Rare Earth Element (REE) concentrations with Sr−Nd−Pb isotope ratios. We observed enrichments in Anthropogenic Rare Earth Elements (AREE) for dissolved (Gd) and suspended (Ce and Nd) loads of river water. During flood events, AREE anomalies progressively disappeared and gave way to the geogenic chemical signature of the basin in both dissolved and suspended loads. The isotopic data confirm these observations and shed new light on the trace elements sources. On the one hand, dissolved loads have peculiar isotopic characteristics and carry mainly limestone-derived and anthropogenic Sr and Nd as well as significant amounts of anthropogenic Pb. On the other hand, the results clearly indicate that anthropogenic contributions impact the suspended loads in all hydrological conditions. This study demonstrates that anthropogenic contributions to the river may change not only Pb but also Sr and Nd isotopic compositions in both dissolved and suspended loads. This is of importance for future provenance studies.
1. INTRODUCTION Processes controlling the chemical composition of natural waters are of major interest for geochemists, hydrologists, and ecologists because they integrate the lithological and chemical variability of their environment and are the main drivers for the transport of elements and particles to the ocean.1−5 The geogenic background is characterized by important variations at regional and local scales. However, elements currently recognized to be undisturbed by human activities and used as tracers of continental crust derived material have become more and more involved in man-induced processes and, therefore, enriched in the environment. Rare earth elements (REE) are now well-established as emergent micropollutants in the dissolved, colloidal, and particulate fractions of river water worldwide.7−10 As a consequence, the natural cycle of all REE is significantly disturbed in river basins impacted by human activities7 and the contribution of anthropogenic rare earth elements (AREE) to surface waters interferes with the geogenic REE sources. However, the identification of the origin of AREE in river systems and the quantification of their impact on ecosystems are still challenging in particular for AREE that may derive from various industrial and urban activities. As stated by ref 9, the composition of the AREE pool is site-dependent and, for a given river system, controlled by the different anthropogenic contributions to the river, which may change from one polluted site to another. For the quantification of the different contributions, it is therefore necessary to use © XXXX American Chemical Society
monitoring tools that allow distinguishment between the REE of different anthropogenic and geogenic origins. The AREE anomaly is a good proxy to quantify anthropogenic contributions for dissolved Gd,3,11 colloidal La and Sm,7 or particulate Ce9,10 but does not always allow for the detection of all anthropogenic pollution in river systems. In order to better constrain the relative contributions of both anthropogenic and geogenic trace element sources we propose using a multitracer approach combining elemental and isotopic tracers such as 87Sr/86Sr, 143Nd/144Nd, and 206Pb/207Pb isotopic ratios. Pb isotopes have been successfully used for a long time in tracer studies and for source discrimination, especially for deciphering anthropogenic and geogenic sources in environmental studies.12,13 Sr and Nd isotopic ratios have been shown to be powerful tracers for source identification in natural surface waters.3,14−16 The approach combining Sr−Nd−Pb isotopic ratios has very recently been successfully tested for the identification and tracing of anthropogenic contributions of atmospheric depositions in urban and industrial areas.17−21 However, the use of these three separate isotopic systems together with REE concentrations is new in the field of anthropogenic source identification. Received: October 1, 2015 Revised: March 22, 2016 Accepted: April 5, 2016
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DOI: 10.1021/acs.est.5b03660 Environ. Sci. Technol. XXXX, XXX, XXX−XXX
Article
Environmental Science & Technology
Figure 1. Characteristics of the upper Alzette River basin and sampling site locations (AS: Alzette Spring; T*: remote location of the Alzette tributaries; T: outlet location of the Alzette tributaries; UA: Upper Alzette; AO; basin Outlet; SI: Steel Industry; S: wastewater treatment plant; WI: waste incinerator). The geological and land cover information came from refs 22 and 23 and were put in ArcGIS to create the maps.
characteristics (limestone, sandstone, marl, waste incinerator (WI), and WWTPs, respectively). The surface water and the WWTP effluent samples were filtered in the laboratory through
