Nutrient availability alters alkyl polyglucoside toxicity to the freshwater microalga Chlorella sp.

Surfactants and nutrients enter aquatic systems simultaneously, forming mixtures that can adversely affect aquatic microalgae in a different way compared to each contaminant alone. Surfactants, such as alkyl poly-glucosides (APG), reduce algal photosynthesis and growth, but the presence of nutrients has been shown to alter the toxicity of some contaminants. We aimed to determine whether the addition of nutrients affects the response of the freshwater microalga Chlorella sp. to APG. Two laboratory experiments were conducted with the same concentration of APG but different nutrient treatments. In the first experiment (+N), algae were exposed to nitrate (NO3-) added in one concentration with or without APG, while in the second experiment (+N+P) NO3- and phosphate (PO43-) were added in two concentrations with or without APG. In the +N experiment, exposure to APG alone decreased cell density by 25 % while the addition of NO3- and APG resulted in densities similar to the control. In the +N+P experiment, the combination of high nutrient concentrations and APG increased cell density to nearly double that in the control and APG-only treatments. The results of this study underscore the importance of determining effects of contaminant mixtures on primary producers in order to better inform water policy and resource management.