Speciation and mobilization of radium in brackish groundwater of agricultural ecosystems

Brackish type groundwater (TDS > 1000 mgL^-1) samples from alluvial aquifers of agricultural ecosystem were analyzed for ²²⁶Ra, ²²⁸Ra, total dissolved U, and physico-chemical parameters. Concentrations values ranged 85 - 479 mBq L^-1 for ²²⁶Ra, 1.7 - 6.6 mBqL^-1 for ²²⁸Ra and 59 - 206 μgL^-1 for total dissolved uranium. The relatively higher ²²⁶Ra activities than ²²⁸Ra could be attributed to local enrichments of dissolved U in groundwaters as obtained by strong positive correlations (R² = 0.50) between ²²⁶Ra-U. However, ²²⁶Ra did not show any correlation (R² = 0.03) with ²²⁸Ra, though both have similar chemical properties, confirming that their input in groundwaters are from different sources such as ²²⁶Ra from decay of dissolved ²³⁸U and ²²⁸Ra from ²³²Th. The positive significant correlation between ²²⁶Ra - salinity and ²²⁶Ra - TDS suggested that radium mobility is being controlled by adsorption-desorption processes. (author)