GENOTOXICITY OF MALATHION IN HUMAN-LYMPHOCYTES ASSESSED USING THE MICRONUCLEUS ASSAY IN-VITRO AND IN-VIVO - A STUDY OF MALATHION-EXPOSED WORKERS

The aerial application of malathion, a widely used organophosphate ins ecticide, has raised public concerns about potential adverse health ef fects. We therefore studied micronucleus formation in human lymphocyte s as a biomarker of genotoxicity both in vitro and in vivo. Lymphocyte s were cultured either as whole blood or after Ficoll isolation and tr eated with malathion in doses from 5 to 100 mu g/ml for 48 h. A signif icant increase in micronucleated cells (47.5/1000 versus 16.0/1000 in DMSO control, p < 0.001) was found in isolated lymphocytes at high dos e levels (75-100 mu g/ml), concurrent with cytotoxicity and a strong i nhibition of proliferation (p < 0.001). Many of the treated cells also possessed multiple micronuclei. Antikinetochore-antibody staining rev ealed that the majority of malathion-induced micronuclei were kinetoch ore-negative. A significant dose-response was also observed in whole b lood cultures, although the increase in micronucleated cells was lower than in isolated lymphocyte cultures (p = 0.03). When the same techni que was applied to lymphocytes of 38 intermittently malathion-exposed workers involved in the Mediterranean Fruit Fly Eradication Program in California, no change in either proliferation or micronucleus level w as observed compared with an unexposed control group. We conclude that malathion has a relatively low potential to cause chromosome damage i n vitro, and corresponding doses are much higher than ones that even p rofessional applicators are likely to be exposed to in vivo. The poten tial risk of chromosome damage for malathion exposure in vivo is there fore relatively low. More studies are needed to assess the possibility of interaction of malathion with other pesticides through combined ex posure.