Ecologic study of mesoscale environments with excess disease prevalence

Paul R. Sheppard, Ph.D., Laboratory of Tree-Ring Research, University of Arizona, Tucson, AZ 85721, sheppard@ltrr.arizona.edu

Joachim D. Pleil, Ph.D., U.S. Environmental Protection Agency, Research Triangle Park, NC 27711, pleil.joachim@epa.gov

Robert J. Speakman, Museum Conservation Institute, Smithsonian Institution, 4210 Silver Hill Road, Suitland, MD 20746, speakmanj@si.edu

Gary Ridenour, M.D., 625 W. Williams, Suite B, Fallon, NV 89406, docridenour@charter.net

Mark L. Witten, Ph.D., Department of Pediatrics, Arizona Health Sciences Center, University of Arizona, Tucson, AZ 85721, mwitten@peds.arizona.edu

In an “ecologic” study of towns with statistically elevated adverse human health outcomes such as clusters of specific cancers, the whole town is considered the “case” subject to be described in environmental terms with respect to chemical loadings in air, water, or soil.  This approach differs from the more commonly used “case-comparison” study where individual sick people are compared with matched control subjects within the same community.  Although a positive relationship in case-comparison is considered to be a definitive indication of cause-effect, this approach is generally inconclusive for rare diseases with long-term latency, such as cancer.  To discern possible environmental associations, an ecologic method has been applied to the broad environmental analysis of a childhood leukemia cancer cluster experienced in Fallon, Nevada.  The chemistry of airborne and surface outdoor dust has been measured and described within Fallon (case) as well as in other nearby similar towns and outlying desert areas (comparison).  Multiple lines of evidence, including airborne dust filtered directly from air, deposited dust collected from ground surfaces, and lichens collected from native bedrock, indicate high levels of airborne tungsten and cobalt within Fallon relative to comparison towns and pristine desert.  Although this finding does not directly link exposure to airborne tungsten and cobalt to childhood leukemia, it does suggest new lines of biomedical research to evaluate if such linkages exist.  More generally, ecologic study can identify distinctive environmental qualities of towns, and those distinctions can then be investigated further in directed public health research.