DNA STRAND BREAKAGE IN FRESH-WATER MUSSELS (ANODONTA-GRANDIS) EXPOSEDTO LEAD IN THE LABORATORY AND FIELD

The sensitivity of a freshwater mussel, Anodonta grandis, to DNA damag e following lead (Pb) exposure was tested in laboratory and field expe riments. Laboratory exposures were conducted for 4 weeks at the follow ing Pb concentrations: 0 (controls), 50, 500, and 5000 mu g/L. Mussels were also collected from a strip-mine pond contaminated with trace am ounts of lead, cadmium (Cd), and zinc (Zn). Significant DNA strand bre akage was observed in foot tissue from mussels exposed in the laborato ry to the lowest Pb concentration (50 mu g/L). No evidence of strand b reakage was observed in any of the analyzed tissues from the mussels e xposed to higher Pb concentrations (500 and 5000 mu g/L) or from the c hronically exposed mussels collected from the strip-mine pond. These d ata suggest a threshold effect for DNA damage and repair resulting fro m low-level Pb exposure, whereby repair of DNA strand breaks may occur only if a certain body burden or exposure duration has been achieved.