DNA damage in mononuclear leukocytes of farmers measured using the alkaline comet assay: discussion of critical parameters and evaluation of seasonal variations in relation to pesticide exposure

The alkaline comet assay was used to quantify, using visual and image analyses, the level of DNA damage in mononuclear leukocytes of farmers who were occupationally exposed to pesticides. Hematological parameters were also measured on the same samples. Enrollment of farmers was based on handling of heavily used pesticides at particular periods during one spraying season. Forty-one blood samples from 29 different farmers were collected at the beginning of the season (n = 11) and at the intermediate (n = 14) and final (n = 16) periods of intense spraying activity. The mean numbers of lymphocytes and eosinophils were nonsignificantly higher in groups 3, 1, and 4 than they were in group 2. No individual characteristics significantly influenced the mean number of lymphocytes or eosinophils, and no correlation was observed between pesticide exposure-related parameters and hematological parameters. The level of DNA damage was significantly (P < 0.01) higher in groups 3, 1, and 4 than it was in group 2. In addition, DNA damage quantification was not significantly different among investigators or among slides. Prescription medicine, alcohol consumption, and age had no statistically significant effect on DNA damage level. Conversely, smoking (smokers versus non- and ex-smokers) significantly influenced DNA damage level (P < 0.0001). A significant (P < 0.05) negative correlation was detected between the number of days without pesticide spraying and DNA damage level, particularly among non- and ex-smokers. DNA damage detected by the alkaline comet assay seems to reflect ongoing exposure to genotoxic agents but not an accumulation of damage.