Cytogenetic effects of the insecticide methamidophos in mouse bone marrow and cultured mouse spleen cells.

The cytogenetic effect of the insecticide methamidophos (0,S-dimethylphosphoroamidothiolate) was studied in mouse bone marrow and mouse spleen cells in culture. In vivo the ability of methamidophos to induce micronuclei and sisterchromatid exchange in mouse bone marrow was investigated. In vitro mouse spleen cells in culture were used to assess the ability of the insecticide to induce chromosomal aberrations and sister chromatid exchange. Three different routes of application for the pure insecticide were tested so as to cover the different possibilities for human exposure to the insecticide. Intraperitoneal, oral and dermal treatment with methamidophos caused toxicity to marrow as indicated by a significant increase in the percentage of polychromatic erythrocytes (PEs) over that of the control. Methamidophos showed mutagenic potential as evidenced by a positive response in the micronucleus and chromosomal aberrations assays. Thus, single and multiple i.p. injections at 6 and 4.5 mg methamidophos/kg body wt., oral administration of the insecticide for 14 consecutive days at a dietary level of 100 ppm and multiple dermal treatments (total 4) with 24 mg/kg body wt. induced a statistically significant increase in the frequency of PEs with micronuclei in mouse bone marrow. Moreover, the tested concentrations of methamidophos as low as 0.25 microgram/ml induced a high percentage of metaphases with chromosomal aberrations in cultured mouse spleen cells. Methamidophos is a weak inducer of SCEs in mouse bone marrow and cultured mouse spleen cells.