Assessing indicators of arsenic toxicity using variable fluorescence in a commercially valuable microalgae: Physiological and toxicological aspects

Indicators signaling Arsenic (As) stress through physiology of microalgae using non-destructive methods like variable fluorescence are rare but requisite. This study reports stress markers indicating arsenic (As) toxicity (in two concentrations 11.25 mu g/L and 22.5 mu g/L compared to a control) exposed to a microalga (Diacronema lutheri), using fast repetition rate fluorometry (FRRf). Growth and physiological parameters such as cell density, chl a and the maximum quantum yield Fv/Fm showed coherence and impeded after the exponential phase (day 9 -day 12) in As treatments compared to the control (p < 0.05). On contrary photo-physiological constants were elevated showing higher optical (aLHII) and functional [Sigma (sigma PSII)] absorption cross-section for the As treatments (p < 0.05) further implying the lack of biomass production yet an increase in light absorption. In addition, As exposure increased the energy dissipation by heat (NPQ-NSV) showing a strong relationship with the de-epoxidation ratio (DR) involving photoprotective pigments. Total As bioaccumulation by D. lutheri showed a strong affinity with Fe adsorption throughout the algal growth curve. This study suggests some prompt photo- physiological proxies signaling As contamination and endorsing its usefulness in risk assessments, given the high toxicity and ubiquitous presence of As in the ecosystem.

Automated summary

Indicators of arsenic (As) stress in microalgae using non-destructive methods like variable fluorescence are rare but important. This study used fast repetition rate fluorometry (FRRf) to measure stress markers indicating As toxicity in Diacronema lutheri. The results showed inhibited growth and physiological parameters, as well as increased optical and functional absorption cross-sections in the As treatments. The study suggests that these photo-physiological proxies can be used to signal As contamination and assess risks.