Evaluation of DNA damage induced by environmental exposure to mercury in Liza aurata using the comet assay

Mercury (Hg) is one of the major aquatic contaminants even though emissions have been reduced over the years. Despite the relative abundance of investigations carried out on Hg toxicity, there is a scarcity of studies on its DNA damaging effects in fish under realistic exposure conditions. This study assessed the Hg genotoxicity in Golden grey mullets (Liza aurata) at Laranjo basin, a particularly contaminated area of Ria de Aveiro (Portugal) well known for its Hg contamination gradient. (1) Fish were seasonally caught at Laranjo basin and at a reference site (S. Jacinto), and (2) animals from the reference site were transplanted and caged (at bottom and surface), for 3 days, in two different locations within Laranjo basin. Using the comet assay, blood was analyzed for genetic damage and apoptotic cell frequency. The seasonal survey showed greater DNA damage in the Hg-contaminated area for all sampling seasons excluding winter. The temporal variation pattern of DNA lesions was: summer approximately autumn > winter > spring. Fish caged at Laranjo also exhibited greater DNA damage than those caged at the reference site, highlighting the importance of gill uptake on the toxicity of this metal. No increased susceptibility to apoptosis was detected in either wild or caged fish, indicating that mercury damages DNA of blood cells by a nonapoptotic mechanism. Both L. aurata and the comet assay proved to be sensitive and suitable for genotoxicity biomonitoring in mercury-contaminated coastal systems.