Differences in Engineered Nanoparticle Surface Physicochemistry Revealed by Investigation of Changes in Copper Bioavailability During Sorption to Nanoparticles in the Aqueous Phase

Abstract

Sorption of chemical substances to nanoparticles (NPs) in the aqueous phase strongly influences NP physicochemisty, and investigations of these complex interactions can provide important insights into the environmental fate of NPs. The objective of the present study was to use differences in copper (Cu) bioavailability to investigate aqueous-phase sorption with NPs that had different physicochemical characteristics (silicon [Si], perovskite, and titanium dioxide NPs [TiO2 NPs]). Sorption of Cu with NPs was assessed by the presence of adsorbent in water and onto the NP surface after ultracentrifugation, and by changes in Cu bioavailability under static conditions during exposure of larval zebrafish, as well as under conditions of continuous agitation during exposure of the alga Chlorella vulgaris. The presence of TiO2 NPs reduced total Cu in the water column and Cu bioavailability (measured by growth inhibition, mortality, and metallothionein 2 gene expression), confirming Cu sorption to TiO2 NPs. Nanoparticle surface area was the most important factor that affected Cu sorption, as indicated by less bioavailable Cu in the presence of smaller TiO2 NPs. The surface area effect was consistent regardless of exposure conditions (alga, continuous agitation; zebrafish, static water) and was further supported by the fact that the lowest total Cu concentration in the water column was found in the presence of the smallest NP. The results differed with other NP types, for example, silicon NPs, in which Cu sorption was indicated by analytical chemistry, but sorption was not sufficient to significantly alter Cu bioavailability. The bioavailability tests did not indicate Cu sorption with perovskite NPs. The results demonstrate that surface area critically influences sorption, that Cu sorption as measured by bioavailability is not affected by agitation or static conditions, and that Cu sorption differs among types of NPs, indicating differences in their surface physicochemistry.