title: The complexity of hair/blood mercury concentration ratios and its implications.
abstract: BACKGROUND
  The World Health Organization (WHO) recommends a mercury (Hg) hair-to-blood ratio of 250 for the conversion of Hg hair levels to those in whole blood. This encouraged the selection of hair as the preferred analyte because it minimizes collection, storage, and transportation issues. In spite of these advantages, there is concern about inherent uncertainties in the use of this ratio.
  
  
  OBJECTIVE
  To evaluate the appropriateness of the WHO ratio, we investigated total hair and total blood Hg concentrations in 1333 individuals from 9 First Nations (Aboriginal) communities in northern Québec, Canada.
  
  
  METHODS
  We grouped participants by sex, age, and community and performed a 3-factor (M)ANOVA for total Hg in hair (0-2 cm), total Hg in blood, and their ratio. In addition, we calculated the percent error associated with the use of the WHO ratio in predicting blood Hg concentrations from hair Hg. For group comparisons, Estimated Marginal Means (EMMS) were calculated following ANOVA.
  
  
  RESULTS
  At the community level, the error in blood Hg estimated from hair Hg ranged -25% to +24%. Systematic underestimation (-8.4%) occurred for females and overestimation for males (+5.8%). At the individual level, the corresponding error range was -98.7% to 1040%, with observed hair-to-blood ratios spanning 3 to 2845.
  
  
  CONCLUSIONS
  The application of the ratio endorsed by the WHO would be unreliable for determining individual follow-up. We propose that Hg exposure be assessed by blood measurements when there are human health concerns, and that the singular use of hair and the hair-to-blood concentration conversion be discouraged in establishing individual risk.
authors.affiliation: School of Occupational and Public Health, Ryerson University, Toronto, ON, Canada. Electronic address: eric.liberda@ryerson.ca.
authors.forename: Eric N
authors.initials: EN
authors.lastname: Liberda
authors.affiliation: Health Studies, and the Department of Physical and Environmental Sciences, University of Toronto Scarborough, Toronto, ON, Canada.
authors.forename: Leonard J S
authors.initials: LJ
authors.lastname: Tsuji
authors.affiliation: Health Studies, and the Department of Physical and Environmental Sciences, University of Toronto Scarborough, Toronto, ON, Canada.
authors.forename: Ian D
authors.initials: ID
authors.lastname: Martin
authors.affiliation: Centre de Recherche du CHU de Québec, QC, Canada.
authors.forename: Pierre
authors.initials: P
authors.lastname: Ayotte
authors.affiliation: Centre de Recherche du CHU de Québec, QC, Canada.
authors.forename: Eric
authors.initials: E
authors.lastname: Dewailly
authors.affiliation: Department of Biochemistry and Biomedical Sciences, McMaster University, Hamilton, ON, Canada.
authors.forename: Evert
authors.initials: E
authors.lastname: Nieboer
mesh_terms: D000293:Adolescent; D000328:Adult; D002648:Child; D005260:Female; D006197:Hair / Q000737:chemistry*; D006801:Humans; D008297:Male; D008628:Mercury / Q000032:analysis* / Q000097:blood; D035501:Uncertainty; D055815:Young Adult
chemical_list: D008628:Mercury
keywords: Aboriginal communities; Hair-to-blood ratio; Methyl mercury; Total mercury