| dc.description.abstract | Chemical pesticides are widely used around the world, but at the same time, they may pose direct or indirect risks to many non-target organisms. Recent increased use of insecticides in coastal areas to control invasive species raises concern that insecticides may affect ecologically and/or commercially important species found in estuaries. In this study, a series of laboratory experiments was conducted to evaluate short-term (lethal) and long-term (sub-lethal) effects of fipronil and imidacloprid on juveniles of brown shrimp and white shrimp. Various concentrations of fipronil and imidacloprid in each experiment were used. The concentrations were determined based on previously observed concentrations in the aquatic environment by other researchers. In the first experiment, five nominal concentrations of fipronil (0.1, 1.0, 3.0, 6.4, and 10.0 μg/L) were used; whereas, in the second and third experiments, lower concentrations of fipronil (0.005, 0.01, 0.1, 1.0, and 3.0 μg/L) and five nominal concentrations of imidacloprid (0.5, 1.0, 15.0, 34.5, 320.0 μg/L) were used. The endpoints of the studies were survivorship, the nominal median lethal concentration (LC50), the nominal median lethal time (LT50), development (weight gain and inter-molt intervals), behavioral and physical changes, and whole-body chemical composition. The main results were as following: (1) Both insecticides affected brown shrimp and white shrimp growth, survival, body composition, body color, and behavior in a concentration-dependent manner; (2) Brown shrimp juveniles were more sensitive to fipronil exposure than white shrimp, with 96-hour LC50 = 0.12 μg/L, which makes brown shrimp one of the most sensitive invertebrates to fipronil studied so far; (3) Under their environmental concentrations, fipronil showed higher impact on juvenile brown shrimp compared with imidacloprid; (4) Fipronil and imidacloprid caused noticeable sub-lethal effects to brown shrimp and white shrimp at concentrations lower than their chronic levels in the aquatic life benchmark of the U.S. EPA. Our results suggest that monitoring of fipronil and imidacloprid should be recommended in estuaries and other areas along the coast near the locations where either fipronil or imidacloprid is used. In addition, it is of importance to reduce the usage of these insecticides especially during the seasons of penaeid shrimp migration to inshore annual nursery areas. Revising the acute and chronic levels of the U.S. EPA aquatic life benchmarks for fipronil and imidacloprid is also recommended to improve the health of estuaries and increase the abundance of shrimp populations in the Gulf of Mexico region. | en |
