The concentrations of dissolved uranium and radium isotopes have been determined in the waters of several Indian rivers. The concentration of uranium (U-238) is found to vary between 0·01–7·0 micrograms/litre, depending primarily on the terrain through which the river flows. From the available data on the activity ratios, U-234/U-238, concentration of U-238 in rivers and the amount of uranium depositing on the ocean floor, a material balance calculation has been attempted. This shows that the supply of uranium to sea by rivers based on above measurements, is inadequate to explain the observed concentrations of U-238 and U-234 in the oceans.

The Ra-226 concentration of river waters is found to be of the order of 0·1 dpm/litre (varying between 0·05–0·2 dpm/litre). The activity ratios, Ra-228/Ra-226, range between 1 and 4. This large variation is clearly related to the fact that the concentrations of the parent nuclides of Ra-226 and Ra-228 are different. The observed ratios are consistent with those expected from leaching of clays/soils; however, analogous to the situation in the case of uranium, the observed concentrations of radium isotopes in the oceans are too large to be explained by their influx by rivers.

Analyses of uranium extracted from South Pacific waters by thein-situ extraction method point to a uniform depth independent value of 1·14 ±0 02 for the U²³⁴/U²³⁸ activity ratio. This value is also the same, within one standard deviation, as that determined for the N. Pacific, S. Indian and Atlantic waters.