This study examines the application of population statistics to laboratory-derived toxicological data for the purpose of developing a predictive model that assesses the population consequences of pollutant and environmentally-induced stress. Life tables are used to calculate age-specific survivorship, fecundity, intrinsic rate of population increase (r), and reproductive value (Va), for populations of Mysidopsis bahia chronically exposed, in separate tests, to mercury and nickel. The population statistics, r, and Va, and pollutant dose are defined quantitatively, and the critical value (r=0) for the intrinsic rate of population increase is compared with traditional toxicological measures of acute and chronic toxicity. The effects of an environmental variable, predation, significantly reduce the critical value (r=0) for the intrinsic rate of growth and demonstrate the interactions of multiple stressors. The use of the population statistic, r, is recommended for estimating the ecological significance of toxicological data and for facilitating the assessment of interactions between pollutant-stressed populations and dynamic environmental pressures.