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. Environ Toxicol Chem 2019;9999:1–11. © 2019 SETAC

Time-Related Alteration of Aqueous-Phase Anthracene and Phenanthrene Photoproducts in the Presence of TiO2 Nanoparticles

“…Irradiated ANT + TiO 2 –NP exposures showed significantly increased cyp 1 a and ephx 2 expression at 4 hpe compared to non-irradiated ANT + TiO 2 –NP exposures (Figure ). Several studies have confirmed that the presence of TiO 2 –NPs enhances ANT photodegradation and results in the production of bioavailable OPAH and OHPAH photoproducts, which is probably responsible for the observed induction of ephx 2 expression in the current study’s irradiated ANT exposures. , Results suggest that initially, photoproducts formed and quickly degraded, but the continued formation caused photoproduct accumulation, thus ensuing biotransformation. , The reduced expression of cyp 1 a (responsible for PPAH metabolism) in non-irradiated ANT + TiO 2 –NP exposures compared to exposures of ANT alone might indicate that ANT was not bioavailable and adsorption to the TiO 2 –NP surface may have occurred, which is consistent with previous studies (Figure S2C; 10, 18). These data further support photocatalytic capabilities of TiO 2 –NPs, considering that ephx 2 (responsible for encoding enzymes that metabolize OPAHs) were further induced in irradiated ANT + TiO 2 –NP exposures compared to exposures of ANT alone (Figure S2A).…”

“…GC–MS analyses for OPAHs and OHPAHs were performed using an Agilent 7890B GC system coupled to an Agilent 5977A mass spectrometer (MS) detector with electron impact ionization. OPAH and OHPAHs were analyzed with optimized methods previously published. ,,, All analyses were run in the selected ion monitoring mode. GC–MS analyses for all analytes were performed in triplicate using an Agilent DB-5MS (30 m × 0.25 mm I.D.…”

“…OPAH and OHPAHs were analyzed with optimized methods previously published. 10,12,14,15 All analyses were run in the selected ion monitoring mode. GC−MS analyses for all analytes were performed in triplicate using an Agilent DB-5MS (30 m × 0.25 mm I.D.…”

“…Several studies have confirmed that the presence of TiO 2 −NPs enhances ANT photodegradation and results in the production of bioavailable OPAH and OHPAH photoproducts, which is probably responsible for the observed induction of ephx2 expression in the current study's irradiated ANT exposures. 10,17 Results suggest that initially, photoproducts formed and quickly degraded, but the continued formation caused photoproduct accumulation, thus ensuing biotransformation. 11,17 The reduced expression of cyp1a (responsible for PPAH metabolism) in non-irradiated ANT + TiO 2 −NP exposures compared to exposures of ANT alone might indicate that ANT was not bioavailable and adsorption to the TiO 2 −NP surface may have occurred, which is consistent with previous studies (Figure S2C; 10, 18).…”

“…Zebrafish (Danio rerio) are incredibly useful in exploring molecular mechanisms of PAH metabolism due to their proven genetic specificity and sensitivity to PAH and NP exposures that have elucidated subsequent changes in the bioavailability of PAHs and their photoproducts, particularly in the presence of TiO 2 –NPs. , In this study, the zebrafish model was employed as a “bioindicator” for the presence of parent PAHs (PPAHs) and their photoproducts through the analysis of genes that encode for enzymes responsible for distinct metabolic events that occur during PAH biotransformation (Phase I: cyp 1 a ; Phase II: ephx 1, ephx 2, and sod 1) to enable unique investigations into the interplay between biotransformation and photodegradation of PAHs over time. In combination with targeted gene expression analyses, diverse OPAHs and OHPAHs were identified and quantified following UVA irradiation of ANT and PHE in both the absence and presence of TiO 2 –NPs.…”