Mechanisms of atrazine selective toxicity in freshwater algae

Atrazine toxicity was determined for a number freshwater green algae and diatoms based on measurements of cell density and chlorophyll a content. Atrazine was extremely toxic to all freshwater algae tested, although there was a broad range of sensitivity among species and between divisions of the algae tested. In general, green algae were more sensitive to atrazine than diatoms. Atrazine uptake and bioconcentration were also investigated. Atrazine was taken up extremely rapidly by all freshwater algae tested. Within each division, different species had different bioconcentration capacities, although the accumulation of atrazine was consistently higher in green algae than diatoms. Atrazine concentrations in the algal cells were much higher than in the medium, although the total amount of atrazine taken up by algae was small relative to the total atrazine in solution (1-3%). The ability to bioconcentrate atrazine in the algae was highly correlated with algal cell volume and surface area, and atrazine uptake was also influenced by atrazine concentrations and algal biomass. A strong relationship was observed between algal sensitivity to atrazine and atrazine bioconcentration or cell volume and surface area. This investigation represents the first examination of detoxification enzymes from freshwater algae and provides evidence of differences among different algal species and groups in detoxification abilities. Freshwater algae have detoxification enzyme systems, especially for glutathione S-transferase and general esterase. Microsomal cytochrome P450 monooxygenase was not detected. Different algal species exhibited differences in detoxification enzyme activity. However, these differences in enzyme activities did not provide strong evidence for explaining the differential responses of algae to atrazine. Results from this study suggest that different sensitivity to atrazine is attributable to different uptake capacity of freshwater algae. Metabolic detoxification may play a minor or no role in determining atrazine toxicity to algae. Relationships observed between cell volume or cell surface area and bioconcentration of atrazine implicate algal cell size as a significant factor in alga/pesticide interaction and subsequent vulnerability to xenobiotics