In the Search for Nanospecific Effects of Dissolution of Metallic Nanoparticles at Freshwater-Like Conditions: A Critical Review

Abstract

Knowledge on relations between particle properties and dissolution/transformation characteristics of metal and metal oxide nanoparticles (NPs) in freshwater is important for risk assessment and product development. This critical review aims to elucidate nanospecific effects on dissolution of metallic NPs in freshwater and similar media. Dissolution rate constants are compiled and analyzed for NPs of silver (Ag), copper (Cu), copper oxide/hydroxide (CuO, Cu­(OH)2), zinc oxide (ZnO), manganese (Mn), and aluminum (Al), showing largely varying (orders of magnitude) constants when modeled using first order kinetics. An effect of small primary sizes (<15 nm) was observed, leading to increased dissolution rate constants and solubility in some cases. However, the often extensive particle agglomeration can result in reduced nanospecific effects on dissolution and also an increased uncertainty related to the surface area, a parameter that largely influence the extent of dissolution. Promising ways to model surface areas of NPs in solution using fractal dimensions and size distributions are discussed in addition to nanospecific aspects related to other processes such as corrosion, adsorption of natural organic matter (NOM), presence of capping agents, and existence of surface defects. The importance of the experimental design on the results of dissolution experiments of metal and metal oxide NPs is moreover highlighted, including the influence of ionic metal solubility and choice of particle dispersion methodology.

A Review on the Environmental Fate Models for Predicting the Distribution of Engineered Nanomaterials in Surface Waters

“…Dissolution of ENMs can be considered as chemical transformation processes of ENMs from particulate forms into dissolved ions as shown in Figure 1 . Dissolution is particularly relevant for metallic and metal oxide ENMs, such as AgNPs, ZnO NPs, and copper oxide nanoparticles (CuO NPs), which have been shown to dissolve to Ag + , Zn 2+ , and Cu 2+ , respectively, in aqueous solutions [ 83 , 84 , 85 , 86 , 87 ]. In contrast, metal oxide nanoparticles, such as TiO 2 NPs, CeO 2 NPs, and silicon dioxide nanoparticles (SiO 2 NPs), are fairly insoluble in environmental waters [ 31 ].…”

“…Water chemistry factors also affect the dissolution of ENMs. Generally, decreased pH increases the dissolution of metallic and metal oxide ENMs [ 83 , 84 , 85 , 86 , 87 ]. Additionally, agglomeration of ENMs tends to diminish the dissolution rate by reducing the diffusion of species involved in dissolution reactions [ 82 , 87 ].…”

“…Generally, decreased pH increases the dissolution of metallic and metal oxide ENMs [ 83 , 84 , 85 , 86 , 87 ]. Additionally, agglomeration of ENMs tends to diminish the dissolution rate by reducing the diffusion of species involved in dissolution reactions [ 82 , 87 ]. On the other hand, the presence of natural organic matters (NOMs), which are ubiquitous in surface waters, could increase dissolution by enhancing metal solubility through complexation with dissolved metal ions from ENMs [ 87 ].…”

“…Additionally, agglomeration of ENMs tends to diminish the dissolution rate by reducing the diffusion of species involved in dissolution reactions [ 82 , 87 ]. On the other hand, the presence of natural organic matters (NOMs), which are ubiquitous in surface waters, could increase dissolution by enhancing metal solubility through complexation with dissolved metal ions from ENMs [ 87 ]. For carbon-based ENMs, dissolution and aqueous solubility are generally not applicable, although fullerene C 60′ s hypothetical aqueous solubility has been reported at a fairly low concentration of 7.96 ng/L [ 88 , 89 ].…”

Irrigation Water Quality—A Contemporary Perspective

“…Both carbon-based and metal-based nanoparticles are of concern and it has been reported these particles are persistent in water [214,215]. Nanomaterial transformation in fresh water systems is an active field of research [216]. Nanoparticle assessments have concluded that fine particulate matter occurs in a variety of water sources [217][218][219][220][221], so its impact on irrigation water, accumulation in soil, and potential for crop uptake is of paramount significance.…”