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Metal-mixtures in toenails of children living near an active industrial facility in Los Angeles County, California



Children residing in communities near metalworking industries are vulnerable to multiple toxic metal exposures. Understanding biomarkers of exposure to multiple toxic metals is important to characterize cumulative burden and to distinguish potential exposure sources in such environmental justice neighborhoods impacted by industrial operations. Exposure to metal mixtures has not been well-characterized among children residing in the United States, and is understudied in communities of color.


In this study we used toenail clippings, a noninvasive biomarker, to assess exposure to arsenic (As), cadmium (Cd), mercury (Hg), manganese (Mn), lead (Pb), antimony (Sb), selenium (Se), and vanadium (V). We used nonnegative matrix factorization (NMF) to identify “source” signatures and patterns of exposure among predominantly working class Latinx children residing near an industrial corridor in Southeast Los Angeles County. Additionally, we investigated the association between participant demographic, spatial, and dietary characteristics with identified metal signatures.


Through NMF, we identified three groupings (source factors) for the metal concentrations in children’s toenails. A grouping composed of Sb, Pb, As, and Cd, was identified as a potential industrial source factor, reflective of known airborne elemental emissions in the industrial corridor. We further identified a manganese source factor primarily composed of Mn, and a potential dietary source factor driven by Se and Hg. We observed differences in the industrial source factor by age of participants, while the dietary source factor varied by neighborhood.


Utilizing an unsupervised dimension reduction technique (NMF), we identified a “source signature” of contamination in toenail samples from children living near metalworking industry. Investigating patterns and sources of exposures in cumulatively burdened communities is necessary to identify appropriate public health interventions.

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Fig. 1: Map of study area.
Fig. 2: NMF analysis results.


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We would like to thank our study participants, our community partners, Dayane Duenas Barahona and all volunteers that supported our study staff for assistance with this study. Our deepest gratitude to the Dartmouth Trace Element Core Facility at Dartmouth College in Hanover, NH, which was established by grants from the National Institute of Health (NIH) and National Institute of Environmental Health Sciences (NIEHS) Superfund Research Program (P42ES007373) and the Norris Cotton Cancer Center at Dartmouth Hitchcock Medical Center.


Southern California Clinical and Translational Science Institute pilot grant pilot grant, NIEHS Southern California Environmental Health Centers (P30ES007048) pilot funding.

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Correspondence to Jill E. Johnston.

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Van Horne, Y.O., Farzan, S.F. & Johnston, J.E. Metal-mixtures in toenails of children living near an active industrial facility in Los Angeles County, California. J Expo Sci Environ Epidemiol 31, 427–441 (2021).

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  • Metal-mixtures
  • Environmental justice
  • Children’s health
  • Biomonitoring


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