Tradescantia-Micronucleus (Trad-MCN) test on the genotoxicity of malathion.

The Tradescantia-Micronucleus (Trad-MCN) bioassay was utilized to determine the genotoxicity of Malathion, a common insecticide. Four different treatment procedures were applied: a) absorption of Malathion/water mixture (with or without DMSO and/or S-9) through the stem, b) spraying a Malathion/water mixture onto the plant cuttings in enclosed chambers, c) spraying a Malathion/water mixture on an open population of plants in the greenhouse, and d) absorption of Malathion fumes through the leaves and buds. Most treatments were administered for 6 hr, followed by a 24-hr recovery time. Slides were prepared from the samples and scored for micronucleus (MCN) frequencies. Results of 16 experiments indicated that the genotoxicity of liquid Malathion absorbed through the stem was very low and often masked by high toxicity, causing dead cells in the stem, leaves, and meiocytes. Malathion spray at the dosage of 0.435% in an enclosed chamber or on an open population of plants yielded negative responses. Malathion fumes at dosages of 0.15-0.25% induced significantly higher (0.05) MCN frequencies above the controls and altered the nuclear structure to form unequal sized nuclei and multiple breaks in each of the four cells of a tetrads. It also caused degeneration of nuclei, "protrusions on nuclei," and inhibition of cell growth. Higher dosages (above 0.25%) were toxic.