Genetic monitoring of malathion-exposed agricultural workers

The aerial application of malathion over large urban populations in Southern California during the early 1990s raised concerns about adverse health effects, including the potential to cause genetic damage. Workers in the Mediterranean fruit fly eradication program, which involved application of malathion as ground treatment, were studied to examine micronucleus formation and mutation frequencies assessed by the glycophorin A (GPA) assay. In the 1992 pilot project the mean micronuclei level appeared higher in lymphocytes of exposed workers (n = 13) compared to controls (n = 4) (20.1 +/- 7.1 vs 14.3 +/- 7.2 respectively, P = 0.09). During the 1993 season, neither of the cohorts examined showed a higher level of micronuclei in workers exposed to malathion compared to unexposed, nor did the pooled total (n = 53; means = 17.8 +/- 7.2 vs 18.5 +/- 6.3, respectively), even after adjustment by multiple regression. The GPA variant frequency was not associated with malathion exposure in any of the cohorts. These results suggest that any potential risk of genotoxic damage from exposure to malathion is relatively low, but other assays may be more sensitive, and the sample size was small.