Subcellular Accumulation and Depuration of Zinc in Periphytic Algae during Episodic and Continuous Exposures

As the severity of extreme precipitation events increases with global climate change, so will episodic pulses of contamination into lotic systems. Periphytic algae represents bioindicator species in most freshwater systems due to their rapid accumulation of toxicants; therefore, it is vital to understand how accumulation in this group differs across temporally variable exposure regimes. The ability to rapidly accrue contaminants has additional implications for the trophic transfer of metals to primary consumers. While dietary toxicity has been studied in algivorous consumers, techniques used to prepare contaminated periphytic algae for consumption have not been compared. This study used a modified subcellular fractionation method to compare the partitioning of zinc (Zn) in periphyton cultures exposed for various durations (cultured in the presence of Zn and 15 min, 24 h, and 48 h exposures). Three exposure groups were additionally depurated over a period of 24 h in order to compare retention of Zn, an important aspect of preparing diets used in dietary toxicity studies. The results not only provide evidence for increased retention by periphytic algae cultured in the presence of Zn but reveal relationships among treatments and subcellular partitioning that suggest time-dependent accumulation and detoxification. These relationships suggest that episodic exposure of periphytic algae to contaminants may pose a greater risk than that of chronic regimes. Based on these results, we additionally advocate for culturing periphytic algae in the presence of contamination to produce a more reliable diet for dietary exposure testing in algivorous organisms.