The stability of Ag and ZnO engineered nanoparticles in Hoagland's nutrient water: the role of particle size and morphology

Abstract

The current study seeks to investigate the dissolution dynamics of silver (nAg) and zinc oxide (nZnO) engineered nanoparticles (ENPs), and how this affects their uptake by aquatic higher plants. First, the influence of particle size and morphology on the stability of nAg and nZnO in Hoagland’s nutrient medium will be investigated. The nutrient medium will be dosed with ENPs concentrations ranging from 1-1000 µg/L whereby the dissolved metal ions will be quantified using the ICP-OES with a detection limit of 1 µg/L. Dry powder ENPs will be characterised for size, size distribution, and morphology using TEM, surface area using BET, surface charge using Zetasizer, and surface crystallinity using XRD. In Hoagland’s media, the ENPs hydrodynamic size and surface charge as well as particle counts will be determined using Zetasizer and NTA, respectively. Secondly, the study will investigate the uptake dynamics of nAg and nZnO by an aquatic higher plant Spirodela punctuta, and evaluate their toxicity over a 20 day period. The role of hydrodynamic size, particle morphology as well as media ionic strength on ENP uptake and toxicity will be examined. Uptake investigations will be undertaken through SEM imaging inspection of plant sections whilst OxiSelect assay kits will be used to evaluate catalase activity, protein carbonyls, and free radical activity to ascertain potential ENPs linked induced toxicity. Through timeous analysis of chemical and physical state of ENPs, the proposed study envisages to generate detailed data useful to support sound hazard assessment and ultimately the risk assessment of metallic- and metal oxide-ENPs towards higher aquatic plants.