The Desorption of Silver and Thallium from Soils in the Presence of a Chelating Resin with Thiol Functional Groups

Silver (Ag) and thallium (Tl) are non-essential elements that are toxic to many biota at trace levels, but are rarely studied in soil environments. Ag sorbs strongly to soils, especially those rich in organic matter whereas Tl sorption is influenced by clay content. However, the mobility and bioavailability of Tl and Ag are ultimately affected less by the soil sorptive capacity than by the ease with which these elements desorb from soils. In that context, the strength of Ag and Tl sorption to illite-rich mineral soils with differing textures and an organic peaty-muck soil, from New York State, was investigated by studying their desorption using, as a sink for the metals, a resin (Duolite G-73) containing a thiol functional group. Desorption was monitored over time (1 h, 4 weeks) from soils previously equilibrated with Tl+ or Ag+ for 24 h (steady-state) or for up to 1 year. Within 24 h, 60% of the sorbed Tl was recovered by the resin. Within 2 weeks, 80–100% of the Tl desorbed from all four soils equilibrated for both 24 h and 1 year periods. Ag was not effectively recovered from the resin. However, qualitative review indicates that more Ag was desorbed after the 24 h sorption period than after the 1 year period. More Ag desorbed from the sandy soil than from the peaty-muck soil or the mineral soils with higher clay contents. However, within two weeks silver was mobilized from the peaty-muck soil. The observed release of Ag and Tl from soils, coupled with their toxicity at trace levels to a broad range of soil organisms, suggests that they may pose an environmental concern when present in soils at elevated concentrations.