Effect of fluoride on the cell viability, cell organelle potential, and photosynthetic capacity of freshwater and soil algae.

Although fluoride occurs naturally in the environment, excessive amounts of fluoride in freshwater and terrestrial ecosystems can be harmful. We evaluated the toxicity of fluoride compounds on the growth, viability, and photosynthetic capacity of freshwater (Chlamydomonas reinhardtii and Pseudokirchneriella subcapitata) and terrestrial (Chlorococcum infusionum) algae. To measure algal growth inhibition, a flow cytometric method was adopted (i.e., cell size, granularity, and auto-fluorescence measurements), and algal yield was calculated to assess cell viability. Rhodamine123 and fluorescein diacetate were used to evaluate mitochondrial membrane potential (MMA, ΔΨ) and cell permeability. Nine parameters related to the photosynthetic capacity of algae were also evaluated. The results indicated that high concentrations of fluoride compounds affected cell viability, cell organelle potential, and photosynthetic functions. The cell viability measurements of the three algal species decreased, but apoptosis was only observed in C. infusionum. The MMA (ΔΨ) of cells exposed to fluoride varied among species, and the cell permeability of the three species generally decreased. The decrease in the photosynthetic activity of algae may be attributable to the combination of fluoride ions (F) with magnesium ions (Mg) in chlorophyll. Our results therefore provide strong evidence for the potential risks of fluoride compounds to microflora and microfauna in freshwater and terrestrial ecosystems.