Investigations of the partitioning of ²¹⁰Po and ²¹⁰Pb in a riverine system in Southeast Michigan, USA

Some of the daughter products in the ²²²Rn-decay series, such as ²¹⁰Po and ²¹⁰Pb, have been widely used as tracers and chronometers in aqueous systems. We measured the concentrations of ²¹⁰Pb and ²¹⁰Po in the dissolved, bulk and particulate phases collected in the Clinton Riverin the Lake St.Clair watershed in Southeast Michigan in order to investigate their partitioning. Activity measurements on the dissolved and particulate phase revealed that approximately 38% and 33% of the total ²¹⁰Pb and ²¹⁰Po in the water column was found in the particulate phase. The activity of dissolved and total ²¹⁰Pb was higher than that of ²¹⁰Po because of the higher atmospheric depositional fluxes of ²¹⁰Pb compared to ²¹⁰Po. Although the calculated K_d values of ²¹⁰Pb and ²¹⁰Po were similar, there was an inverse relationship between the K_ds and suspended particulate matter concentration indicating the presence of particle concentration effect and we attribute this observation to the presence of significant amounts of colloidal ²¹⁰Po and ²¹⁰Pb in the dissolved phase. The fractionation factors for Po and Pb were found to be less than 1 in most cases. The first-order box model calculation-based residence times with respect to scavenging varied from 2 to 25 days for ²¹⁰Pb and 19 to 78 days for ²¹⁰Po. (author)