Investigating the ecotoxicity of metals and metal-oxide nanoparticles in the benthic microalga Cylindrotheca closterium

  • R B Ogunjemilusi

Student thesis: Doctoral ThesisDoctor of Philosophy (PhD)


Coastal aquatic ecosystems such as estuaries are being modified as a result of human-induced environmental pollution. Microphytobenthic assemblages, made up of algae and cyanobacteria (usually dominated by diatoms) are major components of intertidal estuarine sediments. These assemblages occupy key positions as primary producers in aquatic ecosystems acting as source of food to numerous higher organisms (Anderson, 2005). However, despite their importance, these organisms are susceptible to metals and to metal nanoparticles. In this study, the toxicity of Cu and Zn in their ionic and nanoparticulate form was investigated in the benthic diatom C. closterium. The results indicate that the choice of medium can alter the physiology (EPS production, chlorophyll a per cell) and cell size of C. closterium. Media-dependent differences in the toxicity of copper to the diatom were also observed. Combined exposure of Cu and Zinc to the diatom also indicated that both metals may interact antagonistically on C. closterium depending on the concentration ratio of the mixture. The toxicity of metal nanoparticles was also observed to be influenced by the type of test medium. Higher toxicity of CuO and ZnO to the algae was observed in the media without EDTA compared to the medium containing EDTA. Evidence of species-specific sensitivity to nanoparticles was also observed, dependent on the test media in which the nanoparticles was dispersed and the endpoint assessed. The benthic diatom C. closterium (72 h EC50: 0.37 µg L-1) was more sensitive to ZnO NP than the planktonic diatom P. tricornutum (72 h EC50: 0.55 µg L-1) in media without EDTA, using algal growth rate as an endpoint. However, there was no difference in sensitivity between the two diatoms to CuO NP. This study corroborates published findings that have reported metal ions released from metal nanoparticles as the primary mechanism of nanotoxicity.
Date of Award28 Sept 2021
Original languageEnglish
Awarding Institution
  • University of Bristol
SupervisorMarian L Yallop (Supervisor) & Gary L A Barker (Supervisor)

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