RADIUM ISOTOPES IN THE LOWER MISSISSIPPI RIVER

Radium isotopes have been measured in Mississippi River water at several locations between St. Francisville and Venice, Louisiana. Measured activities averaged 11.1 dpm/100 L (disintegrations per minute per 100 L) for dissolved Ra-226 with a Ra-228/Ra-226 activity ratio of 1.04 and a Ra-224/Ra-228 activity ratio of 1.06 for the section of river above a phosphogypsum waste-discharge input. Down river from this site, the dissolved Ra-226 activity averaged 22.4 dpm/100 L with a Ra-228/Ra-226 activity ratio of 0.55 and a Ra-224/Ra-228 activity ratio of 0.87. Chemical and isotopic reequilibration of the radium in the waste with that in the river water and suspended sediments occurs very rapidly. Fluxes of Ra-226 are calculated to be 2.44 x 10(14) dpm/yr (disintegrations per minute per year) for the main stem of the Mississippi during phosphogypsum disposal compared to 0.98 x 10(14) dpm/yr when no phosphogypsum disposal is occurring. Ra-228 flux is calculated to be 1.06 x 10(14) dpm/yr during disposal and 1.01 x 10(14) dpm/yr in the absence of disposal. The radium flux is estimated to be 45% in the dissolved state and 55% in the adsorbed state.