Though circular buffer zones are commonly used in environmental equity assessment, the results obtained may not be entirely accurate because physical processes rarely operate in a perfectly symmetrical manner. An integrated approach, known as geographic plume analysis, accounts for directional biases in the distribution of hazards by using a chemical dispersion model to identify areas that are likely to be exposed to toxic releases. In this paper we implement, evaluate, and compare circular and plume-based approaches to environmental equity analysis in the city of Des Moines, Iowa. For each approach, three strategies were selected to define the spatial extent and form of the buffer used to compute the population at risk. In all cases, the analyses are based on census data units and on locations of hazardous facilities listed in EPA's 1994 Toxic Release Inventory (TRI) database. At each toxic site we generated: (i) circles of radii 0.5 and 1 mile, and (ii) a composite plume footprint based on the chemical released in the largest quantity at each TRI site, and a set of averaged weather conditions. Using 1990 Census data at the block group level of aggregation, the racial and economic characteristics of the population residing within these buffer zones are estimated. The results from each approach were compared to the socio-demographic distribution for the entire city, and to the population that resides outside each type of buffer zone in the city. Our findings indicate that the results of environmental equity are sensitive to both the shape and size of the buffer and the method used to delineate the buffer. In general, a larger proportion of non-whites and individuals below the poverty line are found to reside within the buffers generated using geographic plume analysis.