Abstract
Increased use of pesticide is causing detrimental effects on non-target species worldwide. In this study, we examined the lethal and sub-lethal effects of fipronil and imidacloprid, two commonly used insecticides, on juvenile brown shrimp (Farfantepenaeus aztecus), one of the most commercially and ecologically important species in the United States. The effects of six concentrations of fipronil (0.0, 0.005, 0.01, 0.1, 1.0, and 3.0 μg/L) and six concentrations of imidacloprid (0.0, 0.5, 1.0, 15.0, 34.5, 320.0 μg/L) were tested in a laboratory. We examined five different endpoints: growth, moulting interval, survivorship, behavioral change, and body color change. Growth of shrimp was reduced significantly under higher concentrations of both insecticides. Under fipronil exposure, shrimp in control showed the shortest inter-moult interval (7.57 ± 2.17 day) compared with other treatments; similarly, in the imidacloprid experiment, moulting increased from 8.43 ± 2.52 day in control to 11.95 ± 4.9 day in 0.5 μg/L treatment. Higher concentrations of fipronil (1.0 and 3.0 μg/L) showed a 0.0% survival rate compared with 100% survival in the control and 0.005 μg/L treatment. Under imidacloprid, survivorship decreased from 100% in the control to 33.33% in the 320.0 μg/L treatment. The 96-h LC50 of fipronil was 0.12 μg/L, which makes brown shrimp one of the most sensitive invertebrates to the pesticide. Changes in behavior and body color were observed under both insecticides after different durations of exposures depending on concentrations. We conclude that, at the corresponding EPA benchmark concentrations, fipronil had more lethal effects than imidacloprid, and imidacloprid had more sub-lethal effects than fipronil. Both effects are of serious concern, and we suggest monitoring is necessary in estuaries.
Highlights
The initial weight of shrimp exposed to fipronil was not significantly different among all treatments, and the treatment means ranged between 0.56 ± 0.04 g in the 0.01 μg/L treatment and 0.59 ± 0.03 g in the 0.005 μg/L treatment (ANOVA, P = 0.973)
Final weight of shrimp ranged between 1.02 ± 0.12 g in the 0.1 μg/L treatment and 1.31 ± 0.07 g in the control (0.0 μg/L), which was significantly different from other treatments except the 0.005 μg/L treatment under which the final weight was 1.30 ± 0.03 g (ANOVA, P < 0.0001) (Fig 1A and S3 Table)
Fipronil affected the percent weight gain of shrimp, and significant differences were observed between the control (125.92 ± 28.42%) and the 0.1 μg/L treatment (77.007 ± 21.83% weight gain) (ANOVA, P < 0.0001) whereas there was no significant difference between lower fipronil concentrations (0.005 μg/L and 0.01 μg/L) and the control
Summary
Because chemical pesticides eventually flow into the surface water, it is expected these toxicants to affect aquatic environments more than terrestrial environments [10]. These negative effects could be acute (lethal) or chronic (sub-lethal) and vary depending on species [11, 12], the majority of ecotoxicological studies neglect their sub-lethal effects [13, 14] and focus on selected model species, such as daphnia Daphnia magna and zebrafish Danio rerio [2, 15]. We present the results of experimental studies on the effects of fipronil (5-amino-1-[2, 6-dichloro4-4(trifluoromethyl) phenyl]-4[(trifluoromethyl) sulfinyl]1H- pyrazole-3-carbonitrile) and imidacloprid (1-[(6-Chloro-3-pyridinyl) methyl]-N-nitro2-imidazolidinimine), two of the most commonly used chemical pesticides worldwide on brown shrimp F. aztecus
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