7.3 percent, respectively), of people with incomes below the poverty level (19.0 and 13.1 percent, respectively), and of people on welfare (13.3 and 8.3 percent, respectively). These results are congruent with those from the United Church of Christ Commission for Racial Justice.

American Indians have also been the focus of concerns about exposure to environmental hazards. For example, uranium ore was discarded on Navajo lands in New Mexico during the 1950s (Johnson and Coulberson, 1993). An investigation by the Agency for Toxic Substances and Disease Registry found radiation levels in private residences high enough to cause health concerns, and the discarded ore was removed by the Environmental Protection Agency (EPA) and the Navajo Superfund office. Although it is not currently possible to know the extent to which the environmental concerns faced by American Indians are unique to them, additional site-specific health surveillance studies of this population are under way (Johnson and Coulberson, 1993).

The establishment of causal relationships between a health condition and the siting of environmental hazards in proximity to low-income or minority communities is a complicated and debatable exercise. Were waste sites purposely located in these communities because of discriminatory motivations, because of the lack of politically effective opposition, because land was cheap, or because of a combination of these and other factors? Were the communities characterized by the same socioeconomic and racial or ethnic indicators when the waste sites were originally established, or did the composition of the communities evolve later, as a result of economic or other factors? The economics of land values, job opportunities, and transportation undoubtedly assert a strong influence on these outcomes, and the circumstances undoubtedly vary greatly from locale to locale. For the purposes of this report, however, the committee did not believe that it was essential to try to reach conclusions about causality or motivation; no matter how a particular condition came to be, if it represents an environmental health hazard and if the burdens of such a hazard are borne inequitably, then it is appropriate to assess the scope and severity of the health burden and to evaluate potential means of ameliorating it.

Characterizing Exposure

Proximity to a source is an inexact surrogate of actual contact with toxicants from the source. Quantification of the actual emissions from the source moves the analysis a step closer to measuring actual human exposure to an environmental health hazard. This requires estimating the rate of release and the path of the material into and through the environment. For example, in one community that the committee visited (Tucson, Arizona), a common industrial practice, begun in the 1940s, was dumping organic-solvent waste into earthen ponds. This source released toxicants in two ways: (1) the solvents evaporated from the ponds, creating an airborne means of exposure for workers and the residents in surrounding communities, and (2) the solvents migrated from the ponds into the



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