Metal Mixtures in Urban and Rural Population in the United States: Evidence from the Multi-Ethnic Study of Atherosclerosis and the Strong Heart Study
Embargo until
Date
2015-04-22
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Johns Hopkins University
Abstract
Introduction: Natural and anthropogenic sources of metal exposure are different for residents of urban and rural areas. The objectives of this study were to evaluate metal-mixtures and allocate potential environmental sources of different urinary metals, and to compare metal-mixtures in two population-based studies in the United States: the Multi-Ethnic Study of Atherosclerosis (MESA) conducted in 6 urban areas, and the Strong Heart Study (SHS) conducted in 3 rural areas.
Methods: We studied 308 White, Chinese, Black and Hispanic adult participants in MESA (2000-2002 examination), and 105 American Indian adult participants in SHS (1998-2003 examination). Participants were selected at random and stratified by site for metal measurements. Nine metals (As, Cd, Mo, Pb, Sb, Se, U, W and Zn) were measured in spot urine specimens by inductively coupled plasma-mass spectrometry. For arsenic, we used the sum of inorganic and methylated species (∑As). We used principal component analysis (PCA), cluster analysis (CA), and linear discriminant analysis (LDA) to evaluate metal-mixtures. We accounted for urine dilution by standardizing metal concentrations by specific gravity.
Results: Levels of ∑As, Cd, U, W and Zn were higher in SHS participants as compared with MESA participants. PCA and CA revealed consistent patterns in SHS, suggesting 4 distinct principal components (PC) or clusters (∑As-U-W, Mo-Se, Pb-Sb, Cd-Zn). In MESA, CA showed 2 large clusters (∑As-Mo-Sb-U-W, Cd-Pb-Se-Zn), while PCA showed 4 components (Sb-Se-Zn, Pb-U-W, Cd-Mo, ∑As-Pb). After adjusting for rice intake in MESA, PCA and CA showed more similar findings. LDA indicated that ∑As was the most discriminant variable distinguishing MESA and SHS participants.
Conclusions: The ∑As-U-W urinary cluster and PC in SHS might reflect groundwater contamination in rural areas. The Cd-Zn cluster and PC in SHS could reflect common sources from processed meat and interactions in metabolic pathways for those metals. Among our 9 metals, ∑As had the highest discriminant ability to distinguish participants from MESA and SHS, reflecting disproportionate inorganic arsenic exposure in rural tribal communities compared to urban communities around the US.
Description
Keywords
metal