Investigating The Effects Of Titanium Nanoparticles On Freshwater Benthic Algae

Abstract

Titanium dioxide nanoparticles (n-TiO2s) possess a range of unique physico-chemical properties, which makes them differ greatly from their bulk counterparts. These unique properties make them highly desirable, and they are used in a broad range of cosmetic, textile and medical products. Increasing consumer demands are expected to drive worldwide production up to 2.5 million tonnes/year by 2025. The amount of n-TiO2s entering freshwater bodies is increasing, causing concerns about the potential toxic impacts on freshwater biota, including microalgae. Previous studies have shown that freshwater algae are negatively affected by the presence of n-TiO2s, however, most of this research has focused on the effects on green, planktonic algal species. Due to the high sedimentation rate of n-TiO2s, the benthic sediment may be a temporary repository, and benthic algae may be more at risk of n-TiO2 exposure.

The main aim of this thesis was to investigate the impacts of n-TiO2 on benthic freshwater algae. The two main objectives were (i) to quantify the impacts of n-TiO2s on the growth and photophysiology on a single species benthic diatom, Nitzschia palea and (ii) to quantify the impacts of n-TiO2s on the biomass, photophysiology and species composition of whole benthic biofilm communities in outdoor artificial mesocosms using river water from the River Frome (Dorset, UK).

Increasing n-TiO2 concentration exerted an acute toxic effect on benthic algae. Exposure to n-TiO2 negatively impacted the growth and photophysiology of N. palea in the laboratory and negatively impacted the photophysiology and pigment concentration of biofilm communities in the field. Negative impacts were more pronounced in the field, as biofilms were impacted by lower n-TiO2 concentrations, suggesting N. palea may be a relatively tolerant species. Negative effects, both in the laboratory and field, were less pronounced after 72 hours.

This research confirms that n-TiO2s negatively impact benthic algal communities and highlights the need for extensive testing of n-TiO2 on benthic species. The use of mesocosm experiments in nanotoxicology is vital for understanding the toxicity impacts in the field, which may be under-estimated in the laboratory due to field conditions potentially altering the toxicity of n-TiO2s. Due to the variability in algal response to n-TiO2 throughout the literature, future research should consider how methodological variations can change the toxicity profile of n-TiO2s, leading to the production non-comparable and non-reproducible data.

Date of Award	1 Oct 2019
Original language	English
Awarding Institution	University of Bristol
Supervisor	Marian Yallop (Supervisor) & Gary Barker (Supervisor)