Groundwater Contamination by Uranium and Mercury at the Ridaura Aquifer (Girona, NE Spain).

Andrés Navarro,Manuel Viladevall,Xavier Font

doi:10.3390/toxics4030016

Andrés Navarro, Manuel Viladevall + Show 1 more

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https://doi.org/10.3390/toxics4030016

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Abstract

Elevated concentrations of uranium and mercury have been detected in drinking water from public supply and agricultural wells in alluvial and granitic aquifers of the Ridaura basin located at Catalan Coastal Ranges (CCR). The samples showed high concentrations of U above the U.S. standards and the World Health Organization regulations which set a maximum value of 30 µg/L. Further, high mercury concentrations above the European Drinking Water Standards (1 μg/L) were found. Spatial distribution of U in groundwater and geochemical evolution of groundwater suggest that U levels appear to be highest in granitic areas where groundwater has long residence times and a significant salinity. The presence of high U concentrations in alluvial groundwater samples could be associated with hydraulic connection through fractures between the alluvial system and deep granite system. According to this model, oxidizing groundwater moving through fractures in the leucocratic/biotitic granite containing anomalous U contents are the most likely to acquire high levels of U. The distribution of Hg showed concentrations above 1 μg/L in 10 alluvial samples, mainly located near the limit of alluvial aquifer with igneous rocks, which suggests a possible migration of Hg from granitic materials. Also, some samples showed Hg concentrations comprised between 0.9 and 1.5 μg/L, from wells located in agricultural areas.

Highlights

Elevated concentrations of uranium (U) have been detected in drinking and mineral water in several countries through the world [1]
Ranges (CCR), which consists of two lava mountainous flows, basaltic dikes and necks and hydrothermal volcanic materials belonging to the Quaternary, alignments N60E direction and an elongated basin filled by Tertiary sediments, lava and aflows, set ofbasaltic alluvial terraces, which the most important aquifersbelonging in the region (Figure 1)
Results from this study indicated that U content of major lithologies, mineralizations and sediments reveals that none are extremely enriched uranium

Summary

Introduction

Elevated concentrations of uranium (U) have been detected in drinking and mineral water in several countries through the world [1]. Set a maximum value of 30 μg/L, and the World Health Organization proposed a maximum value of 30 μg/L [3], the European and Spanish legislation [4] does not consider U limitations. Uranium is the most abundant actinide element, reaching values of 2.2–15 ppm in granite [5] showing higher natural concentrations in groundwater related with granitic rocks, rarely these values exceed 20 μg/L. Mean U crustal concentrations are comprised between 0.9 and 1.7 ppm, being somewhat higher in the case of acidic igneous rocks: 2.5–6 ppm [6]. Uranium can show different oxidation states: +4, +5 and +6, being the most abundant species in nature U (IV) and U (VI). In USA aquifers, groundwater affected by the existence of U mineralizations showed concentrations between 1 and 120 μg/L, while in groundwater near U mines concentrations of

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