The environmental distribution and sources of strontium in the case of natural anomaly within the river floodplains

Strontium (Sr) is an alkaline earth metal that substitutes for calcium (Ca) in minerals and could be incorporated into biogenic carbonates and sediments precipitated from water. In the case of the geochemical anomaly of high Sr levels in rocks and sediments, this study determined the origin and spreading among environmental components. The three floodplain zones in the Tula region (Russia) with the suggested high levels of Sr were selected for environmental study. The details of the mineral presence of Sr in typical environment components were found and discussed. The sedimentary rocks as the probable sources of Sr were analyzed by scanning electron microscopy, photon-counting computed tomography, and X-ray diffraction. The levels of Sr were analyzed in components of floodplain ecosystems: substrates, buttercup and shells of the several species of freshwater molluscs. It could be assumed that the strontium-containing mineral in the studied rocks from Zone 1 was celestine (SrSO₄). The highest level of Sr in water (>20 mg/L) was in the underground spring (brook) in Zone 2, which was higher than the established drinking sanitary limit of 7 mg/L. The obtained values in buttercup (Ranunculus repens) were of the same order of magnitude as in plants—hyperaccumulators Alstonia scholaris or Vicia cracca. This indicates the high abundance of Sr in the studied zones, which is reflected in its enrichment in typical aquatic vegetation. The sediments from the studied zones showed an excess of Sr (2635 mg/kg) in the brook at st. 5 and swamp at st. 6 (3336 mg/kg). These values are significantly higher in comparison with the sediments from another regions. The highest levels in shells of freshwater molluscs were found for Zone 3 (10000-12000 mg/kg) on the Ista river. It was concluded that in general, the levels of Sr decreased in the case of high turbidity and low water mineralization.