Understanding the stability of nanoplastics in aqueous environments: effect of ionic strength, temperature, dissolved organic matter, clay, and heavy metals

Abstract

Impact of environmental factors such as temperature, dissolved organic matter, ionic strength and clay colloids on the stability of nanoplastics.

Behavior and Bio-Interactions of Anthropogenic Particles in Marine Environment for a More Realistic Ecological Risk Assessment

“…Stability of plain PS NPs in NSW has been reported in the first hours after the preparation of the suspensions (Mishra et al, 2019), though time-dependent agglomeration that occurred later at 24 and 48 h (Brandts et al, 2018;Tallec et al, 2018;Mishra et al, 2019). From DLS data, Brandts et al (2018) also suggested the sorption capacity of carbamazepine, one of the most common pharmaceuticals found in the environment, onto PS NPs, while NP interaction with heavy metals mostly depends on their speciation in the aquatic environments (Singh et al, 2019). Differently from plain and PS-COOH NPs, once suspended in NSW, positively charged PS NPs usually display a hydrodynamic size close to their nominal diameter (Wu et al, 2019).…”

“…Negatively charged PS NPs, such as PS-COOH NPs, are usually prone to agglomerate in the range of 0.9-1.8 µm soon after dispersion in aqueous media characterized by high ionic strength (>38 ), basic pH, and NOM. Such agglomeration phenomena are largely supported by the DLVO theory and related extensions (Cai et al, 2018;Singh et al, 2019;Wu et al, 2019). Examples are represented by microalgae culture medium (Bergami et al, 2017) and NSW (Della Torre et al, 2014;Bergami et al, 2016;Manfra et al, 2017;Tallec et al, 2018;Grassi et al, 2019), where slight differences in NP agglomerates and size distribution are potentially related to the spatial and temporal variability in seawater chemical composition (i.e., organic matter and ions).…”

“…Once in the marine environment, anthropogenic NPs should not be conceived as single entities, but as a dynamic system of particles interacting with the surrounding ionic species and other colloids. To address these features, several heteroaggregation studies have investigated the individual role of monovalent (NaCl) and divalent salts (MgCl 2 , CaCl 2 ) and their valences on NP behavior and stability as well as NOM model compounds such as fulvic acid (FA), tannic acid (TA), and humic acid (HA) in simplified systems (Romanello and Fidalgo de Cortalezzi, 2013;Cai et al, 2018;Danielsson et al, 2018;Singh et al, 2019).…”

“…On the contrary, once adsorbed onto positively charged PS-NH 2 NPs, HA was able to reverse the surface charge at HA concentrations above 5 mg L −1 , inducing PS-NH 2 to agglomerate at 10 mg L −1 HA (Wu et al, 2019). Divalent cations (e.g., Ca 2+ and Mg 2+ ) present in seawater can induce higher agglomeration of PS NPs, compared to monovalent ones (Na + ) (Cai et al, 2018;Singh et al, 2019). In a CaCl 2 solution containing HA, high ionic valence was found to facilitate bridging effect between nanoplastics and HA, enhancing complexation (Singh et al, 2019).…”

“…Divalent cations (e.g., Ca 2+ and Mg 2+ ) present in seawater can induce higher agglomeration of PS NPs, compared to monovalent ones (Na + ) (Cai et al, 2018;Singh et al, 2019). In a CaCl 2 solution containing HA, high ionic valence was found to facilitate bridging effect between nanoplastics and HA, enhancing complexation (Singh et al, 2019). PS NPs (25 nm) with different surface functionalization have also been shown to easily assemble with DOM in NSW due to hydrophobic interactions, with potential repercussions on carbon dynamics in marine environments even at low NP concentrations (10 µg L −1 ) (Chen et al, 2018).…”