Submitted to: Ecotoxicology and Environmental Safety
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 25, 2005
Publication Date: April 5, 2005
Citation: Stark, J.D., Vargas, R.I. 2005. Population toxicity of the insecticide fipronil to daphnia pulex. Ecotoxicology and Environmental Safety. 62 (1): 11-16. Available:www.sciencedirect.com
Interpretive Summary: In recent years the insecticide fipronil has been used throughout Australia and the Pacific for eradication of invasive fruit fly species. In order to measure non-target effects of this chemical we measured its impact on Daphnia pulex, an important aquatic indicator species. We determined the concentration of fipronil that would lead to extinction of D. pulex populations after single and continuous exposure. We estimated the concentration of fipronil likely to be in the environment based the label recommended application rate. From this information we determined that fipronil could cause damage to wild populations of D. pulex.
The toxicity of the insecticide, fipronil (Regent 4SC), was assessed against Daphnia pulex (Leydig) lethal concentration estimates while chronic toxicity was evaluated with two population growth rate studies. In the first population growth rate study, the instantaneous rate of increase was evaluated after exposure where the pesticide was allowed to degrade over the 10 d time interval. In this study extinction of D. pulex populations occurred after exposure to 0.08 mg/l of fipronil. In the second growth rate study, pesticide concentrations were renewed every other day resulting in exposure to approximately the same concentration over a life-time. The acute LC50 was estimated to be 0.0156 (0.0088-0.083) mg/l. Life tables were developed after exposure to two insecticide concentrations and a control. Exposure to 0.015 mg/l, the approximate 48 h acute LC50, resulted in only a slight decrease in the net reproductive rate compared to the control. Exposure to 0.03 mg/l, the approximate 48 h acute LC60, resulted in a 57% decline in the net reproductive rate. The stable age distribution (after 60 d) of D. pulex changed after exposure to fipronil. Increasing concentrations of fipronil resulted in a decrease in the percent of individuals in juvenile stages, an increase in the adult stage, and no change in the adolescent stage. An expected environmental concentration (EEC) in fresh water lakes/ponds based on an application rate of 123 g ai/ha to corn was estimated to be 0.082 mg/l. This EEC was higher than the LC50, indicating that fipronil could cause damage to wild populations of D. pulex.