Abstract
Bedrock rivers, whose sedimentary geochemistry has been scarcely investigated, are suitable to test geochemical approaches in order to assess the existence and extent of human alterations in the natural abundance of rare earth elements. This work presents the study of REE contents in fine-grained sediments of the (bedrock) Miño River, in an urban reach of its middle course. Different statistical procedures were employed in order to decipher the abundances and patterns of distribution of REE in different environments, showing a higher REE accumulation in surface sediments trapped by potholes and other rock cavities. Background contents were estimated by iterative simple regression. After checking several possible reference elements, Y showed the highest potential for the series of REE from La to Lu. The regression result, namely background function, is very useful to minimize the effect of the natural variability in sediment contents. Background functions also allow for environmental assessment by the calculation of the so-called local enrichment factors. As a general conclusion, contamination, if it exists, is negligible in the area and low enrichments can be attributed to postdepositional processes related to organic matter and the geochemistry of Fe and Mn.
Highlights
Chemical elements that can be found in relatively small contents in the earth’s crust have been used for a variety of proposes since the very beginning of human culture
This work presents the study of Rare earth elements (REE) contents in fine-grained sediments of the Miño River, in an urban reach of its middle course
Different statistical procedures were employed in order to decipher the abundances and patterns of distribution of REE in different environments, showing a higher REE accumulation in surface sediments trapped by potholes and other rock cavities
Summary
Chemical elements that can be found in relatively small contents in the earth’s crust (trace elements, e.g., Au, Ag, Cu, Sn, Pb, Zn) have been used for a variety of proposes since the very beginning of human culture. Developed for common contaminant trace elements should be tested for their potential application to REE In this regard, river sediments are of particular interest, because rivers are principal receivers of human byproducts and wastes. In previous works exploring fluvial potholes and other sculpted forms in bedrock rivers [19,20], the capacity of rock cavities to retain sediments was evidenced, which raised the question of how contaminants accumulate in these peculiar microenvironments. It explored their utility as sediment traps [21]. Last but not the least, background estimation was tested to perform a proper environmental assessment of the measured REE
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