Barium (Ba) contamination in aquatic environments is a growing concern due to its potential adverse effects on ecological systems and human health. Thus, this novel and exploratory study aimed to investigate the potential of a marine and a freshwater microalgae species for barium remediation, with a special focus on the role of intracellular structures known as micropearls, for Ba sequestration.
Through a series of laboratory experiments the marine green microalga Tetraselmis chui, the diatom Phaeodactylum tricornutum and three freshwater (fw) microalgae species (Desmodesmus sp., Tetradesmus sp. and Chlorella sp., all originating from Lake Geneva, Switzerland) were exposed to different Ba concentrations (0.1, 1, 10, 100 and 200 mg/ L) to investigate their overall tolerance to Ba. Resulting growth curves showed no significant differences between 0.1, 1 and 10 mg/L Ba compared to the control, for all five tested microalgae species. The bioremediation experiments testing for Ba accumulation were conducted with T. chui and Desmodesmus sp. using bubble column reactors where they were exposed to 1 mg/L and 10 mg/L Ba concentrations. The uptake of barium by the microalgae was quantified using Microwave Plasma- Atomic Emission Spectroscopy (MP-AES) and revealed a low accumulation of Ba on the biomass of T. chui (with a maximum Ba uptake of 1.9 mg/g for the 10 mg/ L Ba condition and 0.2 mg/g for 1 mg/L condition). For Desmodesmus sp. a Ba uptake of 4.2 mg/g was measured in the biomass after being exposed to 10 mg/ L Ba and 0.8 mg/g in the 1 mg/L Ba condition. No Ba containing micropearls were identified in the fw species used during the experiments. However, scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) revealed the formation of micropearls containing Ba in T. chui.
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