Comet and Micronucleus Assays for Detecting Benzo (a) Pyrene Genotoxicity in Blood Cells of Nile Tilapia (Oreochromis Niloticus) from the Shatt Al-Arab River in Southern Iraq

Abstract

On days 0, 1, 3, 6, and 12, the proportion of DNA strand breakage (determined using the comet test) and micronucleus formation in blood cells were observed in Nile tilapia (O. niloticus) exposed to benzo(a)pyrene at doses of 0, 15, and 30 μg/L. The comet test results showed that the proportion of strand breaks increased with increasing concentrations of benzo(a)pyrene, but levels of DNA damage decreased significantly after 12 days of exposure at all tested concentrations, indicating that the patterns of changes in DNA breakage levels can be explained by the threshold-dependent DNA repair theory. Furthermore, the relatively sluggish development of the DNA damage response and recovery in Nile tilapia blood cells in comparison to prior research utilizing O. niloticus livers suggests that the DNA modification response to benzo (a) pyrene exposure in this species is tissue-specific. Monitoring the frequency of micronucleus formation in fish blood cells during the exposure period revealed a dose-time-response relationship. The significant association between micronucleus induction and DNA strand breaking suggests a probable cause-and-effect relationship between the two types of damage. We propose that genotoxin exposure in the marine environment can be detected by DNA strand breakage and micronucleus formation in fish blood cells.