DOSE-RESPONSE RELATIONSHIP OF ANABAENA-FLOS-AQUAE AND SELENASTRUM-CAPRICORNUTUM TO ATRAZINE AND HEXAZINONE USING CHLOROPHYLL (A) CONTENT AND C-14 UPTAKE

Atrazine and hexazinone were added to unicultural algal cultures of Anabaena flos-aquae (Lyng)(blue-green alga) and Selenastrum capricornutum (Printz) (green alga). Algal biomass was measured using chlorophyll (a) content and physiological activity was measured using C-14 uptake over 1,3,5 and 7 days. Untreated cultures increased in biomass over the first 5 days, leveling off after day 7. Control culture C-14 uptake per mg Chl(a) was highest on day 1 and declined over 7 days. A. flos-aquae biomass and C-14 uptake were inhibited by both herbicides on day 1 and began recovering on day 3 over concentration ranges of 0.1-1.05 mg/l atrazine and 0.7-2 mg/l hexazinone. C-14 uptake for both herbicide treatments was about half of the controls from day 1-3. S. capricornutum biomass and C-14 uptake were not significantly affected by concentrations up to 0.13 mg/l of atrazine; concentrations of 0.23-0.42 mg/l reduced both biomass and C-14 uptake. Hexazinone concentrations of 0.03-0.1 mg/l significantly reduced S. capricornutum biomass and C-14 over 7 days. Effects were generally related to herbicide dose.