Unraveling the hidden pathways: Bioaccumulation and metabolism of atrazine, acetochlor, and metolachlor in aquatic organisms

Abstract

Atrazine (ATZ), acetochlor (ACE), and metolachlor (MET) are widely used herbicides whose residues persist in the environment, contributing to the mixed pollution of aquatic ecosystems. However, the mechanisms underlying their environmental behavior and biological effects remain poorly understood. In this study, we systematically investigated the transfer, bioaccumulation, and elimination of ATZ, ACE, and MET in fish (Procypris merus) under single and combined exposure conditions. The results indicate that after exposure in water, ATZ, ACE, and MET extensively accumulate in the muscle tissue of P. merus, accounting for 71 %–84 % of the total pesticide accumulation, making it the primary storage site for these herbicides. Under mixed exposure conditions, the three herbicides exhibited time-dependent synergistic toxic effects. Combined exposure to ATZ, ACE, and MET significantly increased the concentrations of ATZ and ACE in the liver, as well as the K_up and BCF of ACE and MET. During the purification and detoxification phases, the gills exhibited the highest purification rate, nearly twice that of the intestines and liver. The distribution of herbicides in various tissues was positively correlated with hydrophobicity (log Kow) and lipid content. Using UPLC-ESI-QTOF-MS/MS, the metabolites of ATZ, ACE, and MET were identified and analyzed. The three pesticides were primarily metabolized in the lotus carp through dealkylation, hydroxylation, and conjugation with glutathione/glucose. A total of 9 ATZ metabolites, 11 ACE metabolites, and 10 MET metabolites were identified, 19 of which were detected in fish for the first time. rac-MET displayed distinct stereoselective behavior, with the liver preferentially enriching the 1′S, α′R-MET isomer. This study provides a robust dataset for understanding the environmental and dietary risks of the target herbicides associated with residues that persist for prolonged periods.