Studying the Effect of Soil pH on the Dissolution and Binding of Engineered ZnO Nanoparticles in Soil.

The objective of this research is to explore the role of pH on the binding and dissolution of engineered ZnO nanoparticles (NPs) in soil. Zinc deficiency in crops is widespread across the planet due to low geogenic soil Zn and/or low phytoavailable because of high soil pH, high phosphorous, carbonates, and organic matter content. These factors restrict the efficacy of conventional metal salt fertilizers such as ZnSO₄. In this experiment, we studied the effect of soil pH on the dissolution and partitioning of ZnO NPs to soil water and compared that to ZnSO₄. In addition to naked ZnO nanoparticles, we tested particles with various coatings (phosphate (P), dextran (Dex), and dextran sulfate (Dex-SO₄). Sadler soil obtained from Princeton, Kentucky was adjusted to pH 6 and pH 8 using MgCO₃ and MgO, respectively. Soil was then spiked with the different Zn treatments at 100 mg Zn/kg soil. After 2 weeks of incubation, pressure filtration was performed to extract soil water and inductively coupled plasma mass spectrometry was used to measure the concentration of total and dissolved (after centrifugation) Zn in soil water. We found that at both pH levels 6 and 8, the concentration of total Zn in soil water associated with P- and Dex ZnO NPs was significantly higher than total Zn associated with ZnSO₄. There were significantly higher dissolved Zn concentrations in ZnSO₄ spiked soils water compared to the rest of ZnO NPs at soil pH6, whereas at pH 8, there was no statistically significant difference in dissolved Zn concentration across all nano and ionic Zn treatments. The results indicate that higher total Zn concentrations can be obtained in pore water using engineered ZnO NPs than ZnSO₄. Ongoing studies are being conducted to determine the effect on Zn bioavailability to winter wheat