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

Silver sulfide nanoparticles (Ag₂SNPs) are considered to be stable in the environment due to the extreme low solubility of Ag₂S (K_sp: 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.