title: Chronologically matched toenail-Hg to hair-Hg ratio: temporal analysis within the Japanese community (U.S.).
abstract: BACKGROUND
  Toenail-Hg levels are being used as a marker of methylmercury (MeHg) exposure in efforts to associate exposure with effects such as cardiovascular disease. There is a need to correlate this marker with more established biomarkers that presently underlie existing dose-response relationships in order to compare these relationships across studies.
  
  
  METHODS
  As part of the Arsenic Mercury Intake Biometric Study, toenail clippings were collected at three time points over a period of one year amongst females from within the population of Japanese living near Puget Sound in Washington State (US). Variability in temporal intra-individual toenail-Hg levels was examined and chronologically matched hair and toenail samples were compared to more accurately define the toxicokinetic variability of Hg levels observed between the two compartments.
  
  
  RESULTS
  Mean toenail-Hg values (n=43) for the 1st, 2nd and 3rd visits were 0.60, 0.60 and 0.56 ng/mg. Correlations were as follows: r=0.92 between 1st and 2nd clinic visits, r=0.75 between 1st and 3rd visits and r=0.87 between 2nd and 3rd visits. With few exceptions, toenail-Hg values from any visit were within 50-150% of the individual's mean toenail-Hg level. Nearly all participants had less than a two-fold change in toenail-Hg levels across the study period. A regression model of the relationship between toenail-Hg and hair-Hg (n = 41) levels representing the same time period of exposure, gave a slope (Hg ng/mg) of 2.79 for hair relative to toenail (r=0.954).
  
  
  CONCLUSIONS
  A chronologically matched hair-Hg to toenail-Hg ratio has been identified within a population that consumes fish regularly and in quantity. Intra-individual variation in toenail-Hg levels was less than two-fold and may represent dietary-based fluctuations in body burden for individuals consuming various fish species with different contaminant levels. The chronologically matched ratio will be useful for relating MeHg exposure and dose-response derived from toenail-Hg measurements to those derived from hair-Hg measurements in other studies, and may be useful in future investigations as an indicator of stable MeHg body burden within a population.
authors.affiliation: National Exposure Research Laboratory, U.S. Environmental Protection Agency, Las Vegas, NV, USA.
authors.forename: Thomas
authors.initials: T
authors.lastname: Hinners
authors.forename: Ami
authors.initials: A
authors.lastname: Tsuchiya
authors.forename: Alan H
authors.initials: AH
authors.lastname: Stern
authors.forename: Thomas M
authors.initials: TM
authors.lastname: Burbacher
authors.forename: Elaine M
authors.initials: EM
authors.lastname: Faustman
authors.forename: Koenraad
authors.initials: K
authors.lastname: Mariën
mesh_terms: D000293:Adolescent; D000328:Adult; D044466:Asian People; D004784:Environmental Monitoring; D004785:Environmental Pollutants / Q000032:analysis*; D005260:Female; D006197:Hair / Q000737:chemistry*; D006801:Humans; D008628:Mercury / Q000032:analysis*; D008875:Middle Aged; D009262:Nails / Q000737:chemistry*; D013997:Time Factors; D055815:Young Adult
chemical_list: D004785:Environmental Pollutants; D008628:Mercury