Abstract-The sensitivity of a freshwater mussel, Anodonta grandis, to DNA damage following lead (Pb) exposure was tested in laboratory and field experiments. Laboratory exposures were conducted for 4 weeks at the following Pb concentrations: 0 (controls), 50, 500, and 5000 g/L. Mussels were also collected from a strip-mine pond contaminated with trace amounts of lead, cadmium (Cd), and zinc (Zn). Significant DNA strand breakage was observed in foot tissue from mussels exposed in the laboratory to the lowest Pb concentration (50 g/L). No evidence of strand breakage was observed in any of the analyzed tissues from the mussels exposed to higher Pb concentrations (500 and 5000 g/L) or from the chronically exposed mussels collected from the strip-mine pond. These data suggest a threshold effect for DNA damage and repair resulting from low-level Pb exposure, whereby repair of DNA strand breaks may occur only if a certain body burden or exposure duration has been achieved.

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