Effects of temperature on baseline and genotoxicant-induced DNA damage in haemocytes of Dreissena polymorpha

The potential application of the comet assay for monitoring genotoxicity on freshwater mussel Dreissena polymorpha was explored. A preliminary investigation of the baseline levels of DNA damage in mussel haemocytes and how they were affected by temperature was undertaken. Mussels were kept at four different constant temperatures (4°-18°-28°-37°C) overnight. The withdrawn haemocytes were treated with sodium hypochlorite or melphalan at the established temperatures for 1h. The data obtained showed an amount of DNA damage at increasing temperature both in untreated and treated cells (for example, control tail moment value was 9.04±0.65 at 4°C, 13.40±1.45 at 18°C, 15.50±1.17 at 28°C, and 30.56±0.22 at 37°C). Cell manipulation seems to induce more DNA damage if compared to the control. Furthermore a significant (P<0.001, Student’s t test) interindividual variability appears, probably due to genetic and epigenetic factors (stress, age, diet, reproductive period). In particular the differences observed after treatment could be related to the different response in metabolic terms. A clear dose-response effect is displayed after melphalan treatment. Hypochlorite treatment significantly increases DNA damage even if at lower level than Melphalan treatment. This study demonstrates the potential application of the Comet Assay to haemocytes of D.polymorpha. However, these findings suggest that water temperature could alter both DNA damage baseline levels in untreated animals and their sensitivity towards environmental pollutants. Therefore, more information needs about the seasonal variations and the natural background levels of DNA damage in the wild living mussels before their use for monitoring of genotoxic effects in the aquatic environment.