Effects of inorganic ions and natural organic matter on the aggregation of nanoplastics

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

“…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).…”

“…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).…”

“…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).…”

“…In order to describe these complex interactions, the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory is commonly applied (Romanello and Fidalgo de Cortalezzi, 2013;Cai et al, 2018), although it is restrictive to the balance between electrostatic and van der Waals forces. Several extensions of the DLVO theory have also been proposed to model inter-NP interactions in suspensions, for example, considering surface roughness, hydration forces, and steric effects (Wu et al, 1999;Walsh et al, 2012;Cardellini et al, 2019;Praetorius et al, 2020).…”

“…In order to ascertain NP features in natural exposure media, light scattering [i.e., dynamic light scattering (DLS)] and electrophoretic mobility (EM) analyses are among the most common techniques employed, providing information about NP hydrodynamic size, agglomeration kinetics, and surface charge (da Silva et al, 2011;Ribeiro et al, 2017;Cai et al, 2018;Mourdikoudis et al, 2018). The measurement of ζ-potential (mV) by EM can be used as an indicator of the NP surface charge and, thus, colloidal stability in the medium, with low absolute values usually associated with the screening of NP surface charge (Mourdikoudis et al, 2018).…”