Abstract: Sulfur dioxide (SO₂) is a common air pollutant, present at low concentrations in the urban air, and at high concentrations under occupational exposures. It was produced by combustion and processing of sulfur-containing fossil fuels and was a main component of the gaseous pollutants contributing to the formation of acid rain in China. Consequently, it has become important to study the toxic effects of SO₂ in the environment to human. Vicia faba has been used for evaluating chromosomal aberrations since the early 1920s, and has been proven to be an efficient test system for genotoxicity monitoring of environmental pollutants. It is sensitive and convenient, and produces objective results. The test of Vicia faba was carried out according to Kanaya et al. Dry seeds were soaked for 36 h in distilled water and allowed to germinate on layers of moist cotton at 23℃±1℃ in the dark. Seedlings of Vicia faba, which reached about 20 cm in height, were divided into two groups. One group was exposed to 2.80 mg·m^-3 SO₂ for various durations (4, 4×2, 4×3, 4×4, 4×5, 4×6 h), and the other group was exposed to 28 mg·m^-3 SO₂ for 4 or 4×2 h, each followed by 20 h recovery. Cytogenetic damage was investigated in root and leaf meristematic cells after seedlings of Vicia faba exposed to SO₂. The results showed that mitotic index (MI) decreased, but micronuclei (MN) frequencies increased significantly in both root and leaf meristematic cells comparing to those of the seedlings still incubated in sand. The results also showed that the frequencies of micronuclei in root tips were lower than those in leaf cells when a lay of paraffin was added above the roots incubated in tap water, and higher than those in leaf cells without the separating of paraffin, indicating the importance of water during SO₂ toxic effects occurrence to plants. Present results suggest that SO₂ is genotoxic to root and leaf cells of Vicia faba, and roots of Vicia faba is better to be used as a test system for genotoxicity monitoring of SO₂.

Key words: sulfur dioxide, Vicia faba, micronucleus, cytogenetic damage