COMPARISON OF 2 FRESH-WATER TURTLE SPECIES AS MONITORS OF RADIONUCLIDE AND CHEMICAL CONTAMINATION - DNA-DAMAGE AND RESIDUE ANALYSIS

Two species of turtles that occupy different ecological niches were co mpared for their usefulness as monitors of freshwater ecosystems where both low-level radioactive and nonradioactive contaminants are presen t. The pond slider (Trachemys scripta) and common snapping turtle (Che lydra serpentina) were analyzed for the presence of Sr-90, Cs-137, Co- 60, and Hg, radionuclides and chemicals known to be present at the con taminated site, and single-strand breaks in liver DNA. The integrity o f the DNA was examined by the alkaline unwinding assay, a technique th at detects strand breaks as a biological marker of possible exposure t o genotoxic agents. This measure of DNA damage was significantly incre ased in both species of turtles at the contaminated site compared with turtles of the same species at a reference site, and shows that conta minant-''posed populations were under more severe genotoxic stress tha n those at the reference site. The level of strand breaks observed at the contaminated site was high and in the range reported for other aqu atic species exposed to deleterious concentrations of genotoxic agents such as chemicals and ionizing radiation. Statistically significantly higher concentrations of radionuclides and Hg were detected in the tu rtles from the contaminated area. Mercury concentrations were signific antly higher in the more carnivorous snapping turtle compared with the slider; however, both species were effective monitors of the contamin ants.