AbstractThe dramatically escalating increase in the production and application of titanium dioxide nanoparticles (nano-TiO2) has raised concerns of their risk, due to their extremely small size and high surface area to volume ratio. Increasing amounts of nano-TiO2 are released into the environment intentionally or accidentally, and they are anticipated to accumulate in the estuarine sediments and could impact microorganisms in biofilms. The negative impacts of nano-TiO2 on algae have been widely recorded. However, most of the previous studies have been carried out with planktonic species, with little focus on the benthic species. This research focused on the impact of a commercially available nano-TiO2 product, P25, on selected species of estuarine benthic diatoms from Portishead, Severn Estuary, UK.
Ultraviolet radiation (UVR) was found to play an importance role in determining the impact of nano-TiO2 on the estuarine benthic diatoms. In the presence of fluorescent lighting containing a negligible amount of UVR, the cell density yield and growth rate of Nitzschia cf. clausii, Navicula gregaria, and Cylindrotheca closterium were significantly stimulated by the presence of 100 mg/L nano-TiO2. In the presence of lighting containing a considerable amount of UVR, the cell density yield and growth rate of Cylindrotheca closterium were significantly inhibited by the presence of nano-TiO2, with the 72 h-IC50 being 8.73 mg/L (95% confidence interval of 8.54 – 8.94 mg/L). In the presence of lighting containing a considerable amount of UVR, the total chlorophyll a content in an estuarine microphytobenthos (MPB) community (dominated by benthic diatoms) exposed to 50 – 200 mg/L nano-TiO2 was not significantly different from the untreated MPB, but the phaeopigment concentrations in the treated MPBs were significantly higher, after 1 week and 2 weeks of exposure to nano-TiO2. The genera composition of the MPB diatom community, derived from field samples exposed to 50 – 200 mg/L nano-TiO2, was not significantly different from the untreated MPB, after 1 week of exposure; however, after 2 weeks of exposure, a significant shift was recorded in the genera composition of the diatom community in the treated MPB, with an increase in the relative abundance of the genus Entomoneis and decreases in the relative abundance of genus Navicula and Cylindrotheca, compared to the untreated MPB.
Estuarine benthic diatoms growing on mudflats are subjected to UVR exposure, especially when the tide goes out. Results from this research highlighted that nano-TiO2 could negatively impact the benthic diatom community in the intertidal mudflats of estuaries, which may have further impacts on estuarine primary production.
|Date of Award||24 Mar 2020|
|Supervisor||Marian L Yallop (Supervisor)|