Groundwater radon, radium and uranium concentrations in Região dos Lagos, Rio de Janeiro State, Brazil

Ground water from Região dos Lagos, a coastal area of Rio de Janeiro state, was analysed for 226Ra, 228Ra, 222Rn, 238U, major ion concentrations, and physico-chemical parameters were also measured. Concentrations values ranged from <0.002 to 0.492 Bq l−1 for 226Ra, from <0.01 to 1.50 Bq l−1 for 228Ra and from <1.0×10−4 to 8.0×10−2 Bq l−1 for 238U. Detectable 222Rn concentrations (>3 Bq l−1) were found only in two samples. The spatial distribution of Ra concentration delineated one distinct area and some hot spots with high Ra concentration. Low pH value is the most important water parameter linked to high radium concentration. This is probably related to limited adsorption of radium on soil ferric oxides and hydroxides at low pH range. There was a significant correlation between uranium concentrations and electrical conductivity values, and also between uranium concentrations and concentrations of Ca, Mg, Na, K, and Cl, indicating sea water impact. Uranium concentrations were lower than maximum contaminant level for drinking water, whereas 17 out of the 88 ground water samples had levels of radium that exceeded the maximum contaminant level for tap water. The total annual effective dose for adult due to the water consumption reaches values up to 0.8 mSv.