期刊
ENVIRONMENTAL SCIENCE & TECHNOLOGY
卷 45, 期 20, 页码 9003-9008出版社
AMER CHEMICAL SOC
DOI: 10.1021/es201918f
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资金
- U.S.-EPA [EPA -G2008-STAR-R1]
- U.K.-NERC-ESPRC [EPA -G2008-STAR-R1]
The antibacterial activity of silver nanoparticles (AgNPs) is partially due to the release of Ag+, although discerning the contribution of AgNPs vs Ag+ is challenging due to their common co-occurrence. We discerned the toxicity of Ag+ versus a commercially available AgNP (35.4 +/- 5.1 nm, coated with amorphous carbon) by conducting antibacterial assays under anaerobic conditions that preclude Ag(0) oxidation, which is a prerequisite for Ag+ release. These AgNPs were 20x less toxic to E. coli than Ag+ (EC50: 2.04 +/- 0.07 vs 0.10 +/- 0.01 mg/L), and their toxicity increased 2.3-fold after exposure to air for 0.5 h (EC50: 0.87 +/- 0.03 mg/L) which promoted Ag+ release. No significant difference in Ag+ toxicity was observed between anaerobic and aerobic conditions, which rules out oxidative stress by ROS as an important antibacterial mechanism for Ag+. The toxicity of Ag+ (2.94 mu mol/L) was eliminated by equivalent cysteine or sulfide; the latter exceeded the solubility product equilibrium constant (K-sp), which is conducive to silver precipitation. Equivalent chloride and phosphate concentrations also reduced Ag+ toxicity without exceeding K-sp. Thus, some common ligands can hinder the bioavailability and mitigate the toxicity of Ag+ at relatively low concentrations that do not induce silver precipitation. Furthermore, low concentrations of chloride (0.1 mg/L) mitigated the toxicity of Ag+ but not that of AgNPs, suggesting that previous reports of higher AgNPs toxicity than their equivalent Ag+ concentration might be due to the presence of common ligands that preferentially decrease the bioavailability and toxicity of Ag+. Overall, these results show that the presence of O-2 or common ligands can differentially affect the toxicity of AgNPs vs Ag+, and underscore the importance of water chemistry in the mode of action of AgNPs.
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