Silver release from silver nanoparticles in natural waters.

Area of Science:

• Environmental Science
• Nanotechnology
• Ecotoxicology

Background:

• Increasing use of silver nanoparticles (AgNPs) in consumer products due to antimicrobial properties raises ecological concerns.
• The environmental fate and toxicity of AgNPs depend on their chemical form (zero-valent silver or Ag+ ions), necessitating characterization of AgNP persistence.
• Understanding AgNP dissolution is crucial for predicting their ecotoxicological potential.

Purpose of the Study:

• To evaluate the release of silver (Ag) from AgNPs of varying sizes and capping agents when exposed to river and lake water.
• To determine the influence of nanoparticle size, capping agent, and water chemistry on AgNP dissolution rates.
• To assess the persistence of AgNPs in aquatic environments over a 4-month period.

Main Methods:

• Exposure of 5, 10, and 50 nm AgNPs with polyvinylpyrrolidone (PVP), tannic acid (Tan), or citric acid (Cit) capping agents to river and lake water.
• Monitoring of silver ion (Ag+) release over 4 months.
• Analysis of AgNP dissolution based on mass and surface area.

Main Results:

• Larger AgNPs (50 nm) showed greater resistance to dissolution on a mass basis compared to smaller AgNPs (5, 10 nm) in oxic water.
• Surface-area normalization reduced the observed differences in Ag loss between nanoparticle sizes, highlighting the role of surface area.
• PVP- and Tan-AgNPs exhibited higher Ag+ release rates than Cit-AgNPs.
• Rapid initial Ag+ release was attributed to desorption, with slower oxidative dissolution also occurring.

Conclusions:

• Small AgNPs (5 nm), particularly those capped with PVP or Tan, dissolve rapidly and almost completely in aquatic environments.
• Larger AgNPs (50 nm) can persist for extended periods, potentially serving as a continuous source of Ag+ ions.
• Nanoparticle size and capping agent significantly influence AgNP dissolution and environmental persistence, impacting their ecotoxicological risk.