Fate and lability of silver in soils: Effect of ageing

• Rapid ageing of Ag was observed after 14 days with a decrease in lability of 20–90%.
• A further decrease of 10–40% was observed after 6 months.
• Over time Ag+ formed metallic Ag which was positively correlated to non-labile Ag.
• A positive correlation was found between organic carbon and Ag bonded with sulfur.

The fate and lability of added soluble Ag in soils over time was examined by measurement of labile metal (E-value) by isotopic dilution using the 110mAg radioactive isotope and the solid-phase speciation of Ag by X-ray absorption near edge structure (XANES) spectroscopy. After two weeks of ageing the E-values for Ag decreased by 20–90% with a further decrease of 10–40% after six months. The overall decrease in labile Ag for all soils after the 6 month ageing period was 50–100%. The ageing was more rapid and pronounced in the alkaline soils. XANES results for Ag in soils indicated that for the majority of soils the added Ag+ was reduced to metallic Ag over time, and associations with Fe-oxohydroxides and reduced S groups in organic matter also decreased Ag lability. Strong positive correlations were found between metallic Ag and non-labile Ag and between organic carbon and Ag bonded with S species.