New Insights into the Stability of Silver Sulfide Nanoparticles in Surface Water: Dissolution through Hypochlorite Oxidation.

Silver sulfide nanoparticles (Ag2SNPs) are considered to be stable in the environment due to the extreme low solubility of Ag2S (Ksp: 6.3 × 10-50). Little is known about the stability of Ag2SNPs in surface water disinfected with aqueous chlorine, one of the globally most used disinfectants. Our results suggested that both uncoated and polyvinylpyrrolidone (PVP)-coated Ag2SNPs (100 μg/L) underwent dissolution in surface water disinfected with aqueous chlorine at a dose of 4 mg/L, showing the highest dissolved silver ion concentrations of 22.3 and 10.5 μg/L within 45 min, respectively. The natural organic matter (NOM) and dissolved oxygen (DO) posed effects on the Ag2SNPs dissolution by chlorine; NOM accelerated Ag2SNPs dissolution while DO reduced the rate and extent of Ag2SNPs dissolution. We further demonstrated that Ag2SNPs dissolution was primarily attributed to active oxidative substances including hydroxyl radical and H2O2 originating from the hypochlorite oxidation. Additionally, water containing Ag2SNPs disinfected with hypochlorite showed stronger interference on the zebra fish (Danio rerio) embryo hatching than Ag2SNPs and hypochlorite on their own. This work documented that Ag2SNPs could undergo dissolution in surface water through hypochlorite oxidation, posing potential risks to aquatic organisms, and therefore showed new insights into the stability of Ag2SNPs in natural environment.