Changes in acetylcholinesterase activity in freshwater fish following environmental mercury exposure

Mercury (Hg) is a potent neurotoxin that can become biomagnified via food chains, leading to serious ecological and human health risks. However, despite national monitoring efforts in the Republic of Korea, the neurochemical effects of environmentally relevant Hg levels on freshwater fish remain unclear. Here, we investigate the total and organic Hg levels in 17 freshwater fish species from the Yeongsan River system in Korea, finding total concentrations of 39-1,423 ppb, with organic Hg accounting for 85.7% of this on average. Approximately 25% of specimens exceeded the US EPA consumption guidelines (0.3 ng g-1), indicating potential dietary exposure risks. A significant size-dependent increase in Hg was also observed in Lepomis macrochirus and Zacco platypus, while concentrations of Hg in the brain were negatively correlated with acetylcholinesterase activity. These findings indicate that ecologically consequential neurochemical changes occur following exposure to Hg at environmentally relevant levels and highlight the need for the continuous monitoring of Hg in freshwater ecosystems.