Estimating mutagen mass in indeterminate mixtures: micronuclei in Tradescantia

Short-term biological tests are used to evaluate environmental damage caused by toxic chemicals. Risk or damage to an ecological system exposed to chemicals is assessed using ecological studies or inferences derived from biological-effect data after identification and quantification of contaminants. The compositions of environmental contaminant mixtures are generally indeterminate; there are no direct methods for identifying and comprehensively quantifying all the mutagens, carcinogens, and other types of biologically active chemicals in these mixtures. We present a method for using the induction of micronuclei (MCN) in Tradescantia during the tetrad stage of meiosis to estimate the total quantity of active chemicals. Component identification is not needed. The lognormal distributions of the estimated minimum effective dose (EMED) for 23 compounds tested in solution and 11 tested as vapors (Ma, T. H., Harris, M. M., Anderson, V. A., Ahmed, I., Mohammed, K., Bare, J. L., and Lin, G., 1984, Mutat. Res. 138, 157-167) are used to determine the median-mutagen activity for each exposure route. These activities are 203 mg/liter for aqueous exposures and 14,854 ppm-min for vapor exposures. The method is illustrated using the responses of Tradescantia exposed to a hexachloroethane/zinc chloride aerosol for 30 min at 50 and 100 m. The response at 50 m was equivalent to exposure to a median-active mutagen at 365 ppm for 30 min.