Transformations of Silver Nanoparticles in Environmental Systems

Silver nanoparticles introduced into natural and engineered systems undergo a variety of chemical and physical modifications that dictate their fate, mobility and ecological impact. Key processes include oxidative dissolution, in which Ag⁰ cores release Ag⁺ ions; sulfidation, whereby sulphide species convert surface silver to sparingly soluble silver sulfide; aggregation driven by changes in ionic strength and natural organic matter; and the dynamic formation of surface coronas composed of proteins, humic substances or synthetic coatings. Environmental parameters such as pH, redox potential, sulphide concentration and biological complexity further modulate these transformations. In wastewater treatment plants, rapid sulfidation occurs during anaerobic digestion, vastly reducing ionic release but producing Ag₂S phases that may persist in biosolids. In soils and sediments, depth-dependent gradients of sulphide and oxygen drive heterogeneous particle ageing, resulting in mixed morphologies and variable bioavailability. Surface coatings and protein coronas influence both aggregation and chemical reactivity, altering uptake kinetics in biota. The sum of these processes determines nanoparticle transport, accumulation in organisms and long-term ecosystem effects. Understanding these transformations is essential for robust risk assessment, informed regulation and the design of silver-based materials with reduced environmental footprint.

Research from Nature Portfolio

Recent studies have elucidated the pivotal role of weakly and strongly bound proteins in directing silver nanoparticle sulphidation under biologically relevant conditions. Experiments in serum-containing media demonstrate that the tightly adsorbed protein corona provides nucleation sites for silver sulfide nanocrystal formation, whereas loosely bound proteins impede sulphidation in a concentration-dependent manner. The resulting Ag₂S layers effectively trap released silver ions, reducing acute toxicity. This work highlights how nanoparticle–biomolecule interactions fundamentally alter transformation pathways and toxicity profiles in complex biological matrices.

Transformations of Silver Nanoparticles in Environmental Systems publication trend

The graph below shows the total number of articles in transformations of silver nanoparticles in environmental systems across all publications each year (not limited to Nature Index journals).

Technical terms

Sulfidation: conversion of silver nanoparticles to silver sulfide under sulphide-rich conditions, reducing solubility and altering reactivity.

Protein corona: layer of biomolecules adsorbed onto nanoparticle surfaces that modulates surface chemistry, aggregation and biotransformation.

Mesocosm: controlled outdoor experimental system simulating natural environmental conditions to assess nanoparticle behaviour in complex communities.

Bioaccumulation factor (BAF): ratio of chemical concentration in an organism to that in its environment, reflecting uptake efficiency and retention potential.

Scanning transmission electron microscopy (STEM): high-resolution imaging method combining electron transmission with focused scanning to characterise nanoparticle transformations at the single-particle level.

References

1. Toxicokinetics of Ag from Ag2S NP exposure in Tenebrio molitor and Porcellio scaber: Comparing single-species tests to indoor mesocosm experiments. NanoImpact (2023).
2. Depth-dependent transformation of ZnO and Ag nanoparticles in sulfate-reducing sediments tracked using scanning transmission electron microscopy. Environmental Science Nano (2024).
3. Dynamic protein coronas revealed as a modulator of silver nanoparticle sulphidation in vitro. Nature Communications (2016).
4. Engineered silver nanoparticle (Ag-NP) behaviour in domestic on-site wastewater treatment plants and in sewage sludge amended-soils. The Science of The Total Environment (2020).