P Arayesh - Environment Department, Islamic Azad University, Roudehen, Iran
S Motahari - Environment Department, Islamic Azad University, Roudehen, Iran
R Kazempoor - Department of Biology, Roudehen Branch, Islamic Azad University, Roudehen, Iran
M Farahani - Department of Environment, Roudehen Branch, Islamic Azad University, Roudehen, Iran

The herbicides used in agriculture threaten aquatic ecosystems and biodiversity on a global scale. There are several reports on the residues of currently used herbicides in the tissues of aquatic organisms. This study aimed to determine the effect of concentration on the accumulation of Butachlor in liver tissue in zebrafish fish exposed to sub-lethal concentrations of the toxin. In this study, we investigated the losses and residual toxins in the water and the liver of the zebrafish exposed to sub-lethal concentrations of Butachlor herbicide. This study was performed on ۶۸۰ zebrafish. Initially, to determine the LC۵۰-۹۶ h value, a preliminary pilot study was performed, according to which, the main experiment was then conducted considering four treatments each with three replicates for ۳۰ days. The experimental groups included T۱ (exposure to ۴۰% of the LC۵۰-۹۶ h concentration of Butachlor), T۲ (exposure to ۶۰% of LC۵۰-۹۶ h), T۳ (exposure to ۸۰% of LC۵۰-۹۶ h), and control (C). Mortality was recorded daily. Sampling was conducted from water and liver tissues on the first day and the days ۱۵ and ۳۰ to determine Butachlor residues using gas chromatography (GC). The results showed that Butachlor residue in water was associated with the concentration of the toxin and the exposure time, (T۳>T۲>T۱ groups; p <۰.۰۵). According to the results, the highest mortality and residual Butachlor in the liver tissue were related to the T۲>T۳>T۱> C groups on days ۱۵ and ۳۰ after exposure (p <۰.۰۵) respectively. According to the results of this study, Butachlor herbicide can accumulate in liver tissues of zebrafish even when it is used in low concentrations. Also the behavioral and clinical features following Butachlor use included restlessness, rapid respiration, air swallowing at the surface of the water, loss of balance, and disoriented swimming was observed. Regarding the importance of fish as the protein source in humans’ food, this phenomenon can be a potential threat to human health. Therefore, it is necessary to reduce the application of this toxin and replace it with alternative compounds.

Butachlor, Herbicide, Zebrafish, Bioaccumulation