An extensive series of laboratory experiments was conducted in soil microcosms to study the respiratory response of microorganisms to toxicant amendments within different types of soils. Our analysis of test results demonstrates that coupled biological and environmental factors within soil can be scaled (i.e., commensurably and analogously grouped by means of two rate constants, one characterizing the diffusion of CO2 in the soil matrix and another the biological production of CO2. The two rate constants were used to classify the impact of metal compounds on diverse soil types and to predict the loss or gain of total respiratory CO2 of amended soils relative to intact soils. This method exemplifies a more general approach, potentially useful for scaling complex physical and biological interactions in environmental assessments.