Investigating the ecotoxicity of zinc-oxide nanoparticles on the freshwater benthic diatom Nitzschia palea

Abstract

Zinc-oxide nanoparticles (ZnO-NPs) have gained considerable attention in the last few decades due to their desirable physico-chemical properties. ZnO-NPs are being used in an increasing number of applications in cosmetic, electronic and nanotechnology industries which has inevitably led to increased levels of ZnO-NP pollution in aquatic environments. The high reactivity of ZnO-NPs makes them a potential hazard to aquatic life. Previous studies have reported toxic impacts of ZnO-NPs to freshwater green microalgae, but very little research has focused on benthic species, particularly diatoms. Therefore, the principle aim of this thesis was to investigate the potential toxicity of ZnO-NPs to freshwater benthic diatom, Nitzschia palea. There are currently no standardised, universal toxicity testing guidelines specifically for nanomaterials so an assessment on the suitability of the OECD toxicity testing guidelines for use on N. palea was conducted. Suitable modified guidelines were developed and used in nano-toxicity tests. Inhibitory effects of ZnO-NPs on growth and photophysiology of N. palea occurred in cultures exposed to concentrations of 0.5, 1.0 and 1.5 mg/ L ZnO-NPs. Pulse amplitude modulation (PAM) fluorometry measurements detected changes in photophysiological parameters and was selected as a suitable additional method to determine toxicity. The most pronounced impacts on N. palea were during the first 24 hours of the experimental period. These findings suggest that N. palea is a relatively tolerant species compared to green algae. However, ZnO-NP pollution poses a risk to benthic diatoms which may cause significant disturbances to biofilms that naturally reside in the aquatic environment. N. palea was deemed to be a suitable toxicity testing species and the developed guidelines may provide guidance for future toxicity studies on benthic diatoms. Future studies are recommended to investigate the influence of varied environmental conditions of the toxicity of ZnO-NPs to benthic diatoms.

Date of Award	24 Jun 2021
Original language	English
Awarding Institution	University of Bristol
Supervisor	Marian L Yallop (Supervisor) & Gary L A Barker (Supervisor)