Cytogenetic Evaluation of Malathion Toxicity in Sprague- Dawley Rats

Among organophosphorus pesticides, malathion is considered a relatively safe compound. Malathion, however, functions by inhibiting cholinesterase (ChE) enzymes of the nervous system in both vertebrate and invertebrate organisms. The inactivation of ChE by malathion is therefore a useful indicator of exposure. Because of the increased application of these pesticides, their entry into various environmental systems has become eminent; prompting concern from public health officials. The main objective of this study was to further elucidate the genotoxic potential of malathion using mitotic index (MI) and Structural Chromosome aberrations (SCA) as toxicological endpoints in bone marrow cells of Sprague-Dawley rats. Four groups of 4 male rats each weighing an average of 60±2g were used in this study. Malathion was intraperitoneally injected at the doses of 2.5, 5. 10, and 20mg/kg body weight (BW), and one dose per 24h given for 5 days. A control group was also made of 4 animals injected with 1%DMSO without chemical. Following anesthesia, bone marrow cells were immediately collected from the femur bone. Using standard procedures the mitotic index (MI) and structural chromosome aberrations (SCA) were determined. It was found that the mitotic index significantly decreased as the malathion doses increased. Mitotic indices of 18.4±0.75, 16.1±0.99, 14.1±0.96, 8.87±0.40, and 5.87±0.67% were recorded for malathion doses of 0, 2.5, 5, 10, and 20mg/kg BW, respectively. The results of the chromosomal aberration assay in bone-marrow cells after intraperitoneal treatments with malathion showed an increase in a dose-dependent manner. The mean percentages of induced chromosome aberrations were 1.33±0.58, 5.3±2.5, 7.66±2.1, 11.3±1.5, and 17±2% at malathion doses of 0, 2.5, 5, 10, and 20mg/kg BW respectively. Our results indicate that malathion has the potential to produce genotoxic damage as measured by the mitotic index and chromosomal aberration assays.