PARTITIONING AND TRANSPORT OF PB-210 IN THE OTTAWA RIVER WATERSHED

The partitioning of Pb-210 between dissolved and the suspended sediment phases of the Ottawa River waters has been studied. The results indicate high affinity of the radionuclide for particulates (K(d), 1.9 x 10(5) mL g-1). Companion studies on the precursor Ra-226 give an average K(d) value of 7.8 x 10(3) mL g-1. Nearly 77% of the total Pb-210 (i.e., dissolved plus particulate) and 99% of the total Ra-226 are transported through the system in the dissolved form. The suggestion is made that the low availability of particulates in the system promotes the export of Pb-210 in the dissolved form. The conventional approach gives a mean residence time of about 2000 yr for the atmospherically-derived Pb-210 in the watershed. However, if the flux of this Pb-210 falling directly on the river's surface is taken into account, a mean residence time of about 6200 yr is inferred for this radionuclide in the area soils. This aspect of the study is largely applicable to metals with geochemical behavior similar to that of Pb-210, for the radionuclide itself has a mean life of only 32.2 yr.