Toenails as a biomarker of arsenic exposure in Michigan: Refinements in characterization, validation, and application.

Toenails are used in epidemiological studies to assess arsenic exposure from various environmental pathways. To ensure sound application of the biomarker, validity of this tool must first be considered. The objective of this research is to refine knowledge surrounding toenails as an arsenic exposure biomarker, with application to an ongoing population-based case-control study. Utilizing data from 400 bladder cancer cases and 500 controls, this work aims to establish the exposure-biomarker relationship, investigate intra-individual variability of measurements, and assess the relationship between the biomarker value and disease. Participants residing in an eleven-county region of Michigan with historically high groundwater arsenic concentrations answered questions on demographics, smoking, dietary intake and drinking water intake. Drinking water and toenail samples were collected and analyzed for total arsenic. A subpopulation (n=330) was selected for a follow-up visit during which additional drinking water and toenail samples and drinking water intake data were collected. Drinking water arsenic concentration was a significant predictor (p2=0.32). Inclusion of arsenic intake from consumption of beverages made from tap water markedly increased the correlation (R2=0.48). Arsenic concentrations in drinking water samples were highly correlated over time (r=0.88, p<0.0001, n=196), while a substantial amount of variability was detected between toenail samples collected roughly 14 months apart (r=0.43, p