Aquatic behavior and toxicity of polystyrene nanoplastic particles with different functional groups: Complex roles of pH, dissolved organic carbon and divalent cations

The Mobility of Plastic Nanoparticles in Aqueous and Soil Environments: A Critical Review

“…In the simplest systems containing only a monodispersed suspension of a single type of PNP in deionized water, the colloids will typically be highly stable. Uniform particles will exhibit a similar, non-zero, surface charge that is often retained across a wide range of pH conditions, − and this surface charge will cause them to electrostatically repel each other, helping to maintain their dispersion and stability (Figure a). − Given this stability and their extremely small size, PNPs in suspension are expected to be highly mobile in the environment unless additional variables act to limit their stability. Taking this high potential for mobility as a theoretical baseline, the following sections will discuss how several known environmental variables will affect PNP stability in solution in practice.…”

“…For the simplest systems, this loss of PNP stability can be attributed to the electrostatic charge screening effects of the cations. In the typical suspension containing predominantly negatively charged PNPs, increasing the concentration of metal cations in solution will limit the Debye radius of each particle’s net electrostatic effect. ,, This process minimizes the energy barrier that prevents the particles from approaching each other to the point at which van der Waals attraction will cause them to aggregate (Figure b). ,,, Therefore, PNPs are generally less stable in the water column as the ionic strength increases. ,,,− Multivalent cations (e.g., Ca, Mg, and Fe) will have a stronger charge screening effect at a given mass concentration than monovalent cations (e.g., Na). , In natural solutions, the high ionic strength of seawater, for example, causes a more dramatic increase in PNP aggregation compared to river water and groundwater. ,, In one study, the measured hydrodynamic diameter of unmodified polystyrene PNPs (net negative surface charge) in seawater was nearly doubled compared to that of river water and groundwater due to aggregation . Increasing the ionic strength will, in most cases, limit the fluid mobility of PNPs by decreasing the electrostatic repulsion between particles, causing increased aggregation.…”

“…In addition to their charge screening effects, some metal cations may be adsorbed by the PNPs, which will also decrease the fluid stability of the particles. The adsorption of these cations onto negatively charged PNPs will increase the net surface charge of the particles, moving their ζ potential closer to zero and thereby limiting the repulsive effects between them. ,, Again, limiting electrostatic repulsion between these colloids will increase the effects of van der Waals attraction between them. Larger particles are less prone to destabilization due to metal adsorption because more extensive sorption is required to limit their ζ potential to the point where the particles are no longer electrically stabilized, which may be attributable to the higher Gibbs free energy of adsorption for the larger particles. ,, Exposure to Ca 2+ , for example, was observed to decrease the absolute potential of 50 nm carboxylated polystyrene PNPs by 73%, compared to only 42% for comparable 200 nm particles .…”

Bioavailability and Effects of Polystyrene Nanoparticles in Hydra circumcincta

“…This suggests that the 100 nm NP were more bioavailable to hydra than the 50 nm NP. It is expected from the low salt content in the incubation media that the hydrodynamic behaviour of the NP would not overly change and minimal aggregation would occur [26]. The toxicity was determined in hydra based on morphological changes ( Table 1).…”

Stabilization of Fragmental Polystyrene Nanoplastic by Natural Organic Matter: Insight into Mechanisms

“…Nanoplastics' stability in water is generally determined by measuring changes in their size and sedimentation rates. Using this approach, the stability of nanoplastics has been assessed in natural waters [23][24][25][26][27][28][29][30][31][32][33] , in deionized water with various ionic compositions, ionic strengths, and pHs 21,22,25,31,[34][35][36][37][38][39][40] , in the presence of NOM and suspended sediments 22,23,27,31,33,34,36,[38][39][40][41] and in the presence of extracellular polymeric substances (EPS) 37,42 . Most studies have used polystyrene (PS) latex spheres, which are perfectly smooth, spherical, and monodisperse in size.…”