EFFECT OF ALGAL FOOD CONCENTRATION ON TOXICITY OF 2 AGRICULTURAL PESTICIDES TO DAPHNIA-CARINATA

The effects of algal concentration (Selanastrum capricornatum) on the toxicity of the organochlorine pesticide endosulfan and the synthetic pyrethroid esfenvalerate to Daphnia carinata was investigated. The stu dy progressed through four stages: (1) A dose-response experiment on t he effects of endosulfan and esfenvalerate on the survival, growth, an d reproduction of D. carinata at a single nonlimiting food level. (2) An experiment to investigate the effects of five different food concen trations on survival, growth, and reproduction of D. carinata at suble thal concentrations of endosulfan and esfenvalerate compared with none xposed controls. (3) An experiment to investigate the effects of route of exposure (water, food-borne, or water + food-borne exposure) on th e toxicity of endosulfan to D. carinata. (4) An experiment to investig ate the effects of algal concentration on persistence of endosulfan in the water column and on the relative toxicity of the cu and beta isom ers and of endosulfan sulfate to D. carinata. In the first experiment all daphnids exposed to 500 ng/liter esfenvalerate died within 3 days. There was a significant effect of esfenvalerate on reproduction at 50 ng/liter by the second brood. Endosulfan did not cause significant mo rtality to daphnids but brood size was reduced at 320 mu g/liter. In t he second experiment the toxicity of esfenvalerate increased significa ntly with decreasing food concentration. In contrast, the toxicity of endosulfan to D. carinata was greatest at the higher food concentratio ns. Direct water-borne exposure to endosulfan was the most toxic route of exposure and the presence of algae decreased toxicity of this pest icide. The total amount of endosulfan (alpha + beta + endosulfan sulfa te) persisting in the water column after 24 hr was greater at high foo d levels, suggesting that this may be one mechanism for increased toxi city at high food concentrations. The 48-hr LC(50)s of technical endos ulfan, endosulfan sulfate, alpha-endosulfan, beta-endosulfan, and a 50 :50 mixture of alpha, and beta endosulfan were 478, 756, 249, 205, and 234 mu g/liter, respectively. (C) 1995 Academic Press, Inc.