Genotoxic damage by acute and chronic Benzo[a]Pyrene exposure in Geukensia demissa

Benzo(a)Pyrene (B[a]P), an ubiquitous environmental contaminant, is a polycyclic aromatic hydrocarbon (PAH) that is produced by anthropogenic activity during incomplete combustion. B[a]P is a strong carcinogen, which induces tumors via metabolites in animals. B[a]P is becoming more prevalent in aquatic ecosystems due to mass industrialization, which makes research on its effects on aquatic life crucial. This product can enter into aquatic ecosystems from sources such as urban runoff, fuel exhaust, and oil shipping and refineries. We hypothesized that chronic and acute B[a]P exposure may induce the most potent type of DNA mutation, double stranded DNA breaks (DSBs), and subsequently activate DBS DNA Homologous Recombination (HR) repair pathways. HR is a crucial, error resistant DNA repair pathway, so observing its activity in the presence of DSBs is important to understand how organisms are coping with this genotoxin. Using a molluscan model (Geukensia demissa), we assessed DSB and HR activity, by observing expression of phosphorylated H2AX (y-H2AX) and Rad51, in relation to acute and chronic B[a]P exposure. To asses the effect of chronic, low dose B[a]P exposure, we chose to examine mussels living in an urban B[a]P contaminated site, the Bronx River, and compared them to mussels from a relatively clean site, Greenwich Cove. Western blot analysis of field collected mussels showed that y-H2AX and Rad51 expression was greater in mussels from the urbanized Bronx River than those from Greenwich Cove. y-H2AX is a widely used biomarker for DSBs, and Rad51 is a key enzyme in HR. These data strongly suggests that the chronic low concentration of B[a]P caused increased DSBs and increased HR activity. In addition, our in lab exposures showed a direct causation of DSBs and Rad51 increased expression by B[a]P after both 90 minutes and 24 hours.