Toxicity, Oxidative Stress, and Tissue Distribution of Butachlor in the Juvenile Chinese Mitten Crab (Eriocheir sinensis)

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The Chinese mitten crab (Eriocheir sinensis) is one of the most commercially important crustacean species in China. The aim of this study was to characterize the toxic effects of butachlor (an herbicide of the acetanilide class) on juvenile E. sinensis crabs. The lethal effects and the acute toxicity of butachlor on juvenile E. sinensis specimens were assessed through a semi-static in vitro experiment. We determined the activities of superoxide dismutase (SOD) and catalase (CAT) as well as the levels of glutathione (GSH) and malondialdehyde (MDA) in the gills and the hepatopancreas of the juvenile crabs, at different time points over a 14-day short-term exposure to butachlor. Moreover, we measured the residual levels of butachlor in three different tissues (gills, hepatopancreas, and muscles) of the juvenile crabs over a longer period. Our findings revealed that butachlor is highly toxic for juvenile E. sinensis crabs. In fact, the median lethal concentration (LC50) values of butachlor at 24, 48, 72, and 96 h were found to be 4.22, 1.84, 0.34, and 0.14 mg/L, respectively, while the safe concentration was 0.014 mg/L. The antioxidant defense ability of the juvenile E. sinensis crabs against butachlor was induced after exposure to the herbicide at a concentration of 0.01 mg/L. After 14 days of exposure to butachlor at 0.04 and 0.16 mg/L, both SOD and CAT were found to be significantly inhibited (p < 0.05), the GSH levels were found to be significantly decreased (p < 0.05) and the MDA levels were identified as significantly increased (p < 0.05). Moreover, after 14 days of exposure to butachlor at 0.16 mg/L, the activities of SOD and CAT as well as the content of GSH in the hepatopancreas were found to be significantly decreased (p < 0.05). Our results revealed that a high concentration of butachlor was capable of inducing oxidative stress and damage in juvenile E. sinensis crabs. The maximal residual value of butachlor was obtained in the gills, with a content of 4.56 μg/kg. Butachlor was not detected after 24 days in the aforementioned three tissues of the juvenile crabs, thereby indicating that it was effectively metabolized.