Parkinson's disease mortality and the industrial use of heavy metals in Michigan

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Abstract
Parkinson's disease (PD) mortality rates in Michigan counties for 1986–1988 were calculated with respect to potential heavey metal exposure (iron, zinc, copper, mercury, magnesium, and manganese) from industry based on recent census data. Individuals were counted as a PD death if the diagnosis was listed as an “underlying” or “related” cause of death on the death certificate. Counties with an industry in the paper, chemical, iron, or copper related‐industrial categories (ICs) had statiscally significantly (p < 0.05) higher PD death rates than counties without these industries. Significant correlations of chemical (rs =0.22;p = 0.05), paper (rs =0.22;p = 0.05) and iron (rs =0.29;p = 0.008) industry densities with PD death rates were also present. Counties were divided into high (>15/100,000 individuals 45 years old and over) and low (< = 15/100.000) PD death rate counties by cluster analysis. Geographically, counties with high PD mortality were located mainly in the southern half of the lower peninsula and eastern half of the upper peninsula; low PD death rate counties formed two distinct clusters in the western edge of the upper peninsula and the north‐central portion of the lower peninsula. Other possible risk factors that may explain the varied distribution of PD death rates in Michigan were examined. Those significantly correlated with PD mortality included population density (rs =0.31;p= 0.005), farming density (rs= 0.25;p =0.02), and well water use (rs =−0.24;p =0.03). These ecologic findings suggest a geographic association between PD mortality and the industrial use of heavy metals.