title: Evaluation of γ-radiation-induced DNA damage in two species of bivalves and their relative sensitivity using comet assay.
abstract: Ionizing radiation is known to induce genetic damage in diverse groups of organisms. Under accidental situations, large quantities of radioactive elements get released into the environment and radiation emitted from these radionuclides may adversely affect both the man and the non-human biota. The present study is aimed (a) to know the genotoxic effect of gamma radiation on aquatic fauna employing two species of selected bivalves, (b) to evaluate the possible use of 'Comet assay' for detecting genetic damage in haemocytes of bivalves as a biomarker for environmental biomonitoring and also (c) to compare the relative sensitivity of two species of bivalves viz. Paphia malabarica and Meretrix casta to gamma radiation. The comet assays was optimized and validated using different concentrations (18, 32 and 56 mg/L) of ethyl methanesulfonate (EMS), a direct-acting reference genotoxic agent, to which the bivalves were exposed for various times (24, 48 and 72 h). Bivalves were irradiated (single acute exposure) with 5 different doses (viz. 2, 4, 6, 8 and 10 Gy) of gamma radiation and their genotoxic effects on the haemocytes were studied using the comet assay. Haemolymph was collected from the adductor muscle at 24, 48 and 72 h of both EMS-exposed and irradiated bivalves and comet assay was carried out using standard protocol. A significant increase in DNA damage was observed as indicated by an increase in % tail DNA damage at different concentrations of EMS and all the doses of gamma radiation as compared to controls in both bivalve species. This showed a dose-dependent increase of genetic damage induced in bivalves by EMS as well as gamma radiation. Further, the highest DNA damage was observed at 24h. The damage gradually decreased with time, i.e. was smaller at 48 and 72 h than at 24h post irradiation in both species of bivalves. This may indicate repair of the damaged DNA and/or loss of heavily damaged cells as the post irradiation time advanced. The present study reveals that gamma radiation induces single strand breaks in DNA as measured by alkaline comet assay in bivalves and comet assay serves as a sensitive and rapid method to detect genotoxicity of gamma radiation. This study further indicates that both M. casta and P. malabarica exhibit almost identical sensitivity to gamma radiation as measured by DNA damage.
authors.affiliation: Department of Zoology, Goa University, Goa 403206, India. Electronic address: here.praveen@gmail.com.
authors.forename: M K
authors.initials: MK
authors.lastname: Praveen Kumar
authors.affiliation: Department of Zoology, Goa University, Goa 403206, India. Electronic address: skshyama@gmail.com.
authors.forename: S K
authors.initials: SK
authors.lastname: Shyama
authors.affiliation: Department of Radiation Oncology, Goa Medical College, Goa, India.
authors.forename: B S
authors.initials: BS
authors.lastname: Sonaye
authors.affiliation: Department of Zoology, Goa University, Goa 403206, India.
authors.forename: U Roshini
authors.initials: UR
authors.lastname: Naik
authors.affiliation: Department of Zoology, Goa University, Goa 403206, India.
authors.forename: S B
authors.initials: SB
authors.lastname: Kadam
authors.affiliation: Department of Zoology, Goa University, Goa 403206, India.
authors.forename: P D
authors.initials: PD
authors.lastname: Bipin
authors.affiliation: Department of Zoology, Goa University, Goa 403206, India.
authors.forename: A
authors.initials: A
authors.lastname: D'costa
authors.affiliation: Radiation Biology & Health Science Division, Bhabha Atomic Research Centre, Mumbai, India.
authors.forename: R C
authors.initials: RC
authors.lastname: Chaubey
mesh_terms: D000818:Animals; D015415:Biomarkers / Q000032:analysis; D049872:Bivalvia / Q000528:radiation effects*; D020552:Comet Assay; D004247:DNA / Q000528:radiation effects; D004249:DNA Damage / Q000528:radiation effects*; D005720:Gamma Rays; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D014875:Water Pollutants, Radioactive / Q000633:toxicity*
chemical_list: D015415:Biomarkers; D014875:Water Pollutants, Radioactive; D004247:DNA
keywords: Comet assay; Genotoxicity; Haemocyte; Meretrix casta; Paphia malabarica; γ-Radiation