On the measurement of particulate association of americium in freshwater

A laboratory investigation tested various filtration methods to study the particulate-water fractionation of ²⁴¹Am added to filtered freshwater (Monaco tap water) adjusted to different pH's. By using a system of washed Nuclepore polycarbonate filters, the particulate association (>0.2 or >1 μm) was found to increase hyperbolically with pH and with time, so that less than 1% of the Am was filterable (i.e. retained by a filter) at pH 4.2 and about 5% was filterable at pH 8.2 after 1 day; light had no apparent effect on the filterability of the Am. These values are somewhat greater than those for particle association of Am in seawater but substantially lower than previous estimates of Am particulate association in filtered freshwater. Filter adsorption problems are identified for other filtration systems commonly employed to assess metal particulate association. The results suggest that Am in freshwater is unlikely to form particles to an appreciable extent at pH's ≤8.