Hair Analysis Panel Discussion: Executive Summary

• Spanish Version (En Español)

Executive Summary

The Agency for Toxic Substances and Disease Registry (ATSDR) convened a seven-member panel to review and discuss the current state of the science related to hair analysis, specifically its use in assessing environmental exposures. ATSDR invited a cross section of scientific experts in the fields of hair analysis, toxicology, and medicine to participate in 1½ days of discussions on a variety of topics, including analytical methods, factors affecting the interpretation of analytical results, toxicologic considerations, and data gaps/research needs. The meeting was held June 12 and 13, 2001, in Atlanta, Georgia.

Background

ATSDR convened this panel in response to (1) a growing number of inquiries from community members looking for assistance in interpreting hair analysis results and (2) agency interest in learning more about the utility of hair analysis in evaluating exposures and health effects at hazardous waste sites. The agency hopes to use the input received from this effort to develop guidance for agency health assessors on the use and interpretation of hair analysis data.

The general questions that ATSDR seeks to answer include:

• For what substances do reliable hair analysis methods exist?
• When is it appropriate/inappropriate to consider hair analysis in assessing human exposures to environmental contamination?
• What data gaps exist that limit the interpretation and use of hair analysis in the assessment of environmental contaminants?

This summary report presents the findings of the panel discussions. Central discussion points are highlighted below.

Overview Of Discussions

Panelists engaged in a series of discussions to address ATSDR's questions, pointing to several limitations—having to do with the current state of the knowledge—on the usefulness of hair analysis in assessments of environmental exposures. Discussions focused primarily on metals and trace elements in scalp hair. Panelists considered the distinct differences between using hair analysis to identify exposures (Is the substance reaching people? Does a competed pathway exist?) and using it to predict, diagnose, or treat disease (What do hair concentrations tell us about the likelihood of harmful health effects?). Panelists noted that the latter is where the largest data gaps exist.

Although they were not required to reach consensus, the panelists did agree on the following summary statement related to the overall usefulness of hair analysis in evaluating environmental exposures:

For most substances, insufficient data currently exist that would allow the prediction of a health effect from the concentration of the substance in hair. The presence of a substance in hair may indicate exposure (both internal and external), but does not necessarily indicate the source of exposure.

For what substances do reliable hair analysis methods exist?

The group agreed that laboratory methods exist to measure the levels of some environmental contaminants in hair, but procedures need to be standardized to help ensure more accurate and reliable results (this includes ensuring that samples are collected by a trained person and establishing consistent sampling protocols, washing protocols, quality control/quality assurance procedures, etc.). Further, the panel agreed that testing should be targeted to the specific element of interest.

When is it appropriate/inappropriate to consider hair analysis in assessing human exposures to environmental contamination?

In general, panelists agreed that, before determining the appropriateness of hair analysis as an assessment tool, assessors should consider the following:

1. The exposure type and period. Take exposure histories to understand the likelihood that a particular substance will be in the hair at the time of testing and to identify other exposure sources (e.g., hair treatments).
2. Because the growth rate of hair is on average 12 centimeters per year, the panel concluded that hair analysis is not generally useful for evaluating very recent exposures or those longer ago than 1 year. Segmental analysis of hair (i.e., looking at concentration trends along the length of the hair) may have a role in documenting exposures over time (e.g., identification of a high-dose acute exposure). This would need to be considered on a subject-, substance-, and situation-specific basis.
   
3. The type of substance and its behavior in the body. Determine the biological plausibility that a particular substance will be present in hair and whether it is a marker of external contamination.
4. The group agreed that little is known about the transfer kinetics of substances into hair.
   
5. The clinical relevance of a negative or positive finding. Determine whether any dose-response relationship exists between chemical concentrations in hair and target organ effects/illness. Without an understanding of a dose-response relationship, useful interpretations will not be possible.

The panelists agreed that a relationship between contaminant concentrations in hair and any kind of measurable outcome have only been established for methyl mercury (e.g., the relation between maternal hair levels and observed developmental neurological abnormalities in offspring) and to a limited extent for arsenic (e.g., segmental analysis for forensic analysis), provided external contamination can be ruled out. There may be unique forensic settings for other substances.

The group also indicated the need to evaluate, on a substance- and exposure-specific basis, the extent to which hair analysis may be more advantageous than other biological sampling, such as blood or urine analysis.

What data gaps exist that limit the interpretation and use of hair analysis in the assessment of environmental contaminants?

The group identified several factors that limit the interpretation of even the most accurate, reliable, and reproducible laboratory results. These include:

• The lack of reference (or background) ranges in which to frame the interpretation of results. Assessors need a greater understanding of what is expected to be in hair in the absence of environmental exposures in order to determine whether detected levels are elevated as a result of environmental releases, including possible geographical or regional differences in background levels.
  
• Difficulties in distinguishing endogenous (internal) from exogenous (external) contamination in hair. Being able to make this distinction is important in evaluating internal doses of the substance of interest. The group voiced different views on the effectiveness of washing hair prior to analysis to eliminate external contamination. Some felt that the current literature suggests that there is no reliable washing method capable of separating external contamination from internal deposition of elements. It was suggested that identifying metabolites (or other unique markers of internal exposure) for substances of interest, where possible, is most helpful in distinguishing internal from external contamination.
  
• A lack of understanding of how and to what extent environmental contaminants are incorporated into the hair. Little scientific information is available on the uptake or incorporation of environmental contaminants into hair. Neither kinetic models nor metabolite data are known or fully understood for metals or environmentally relevant organic compounds.
  
• The lack of correlation between levels in hair and blood and other target tissues, as well as the lack of epidemiologic data linking substance-specific hair levels with adverse health effects. These correlations must be understood before hair analysis results can be used as a diagnostic tool or to predict health endpoints. The panel noted that hair analysis is not likely to play a role in evaluations of some of the more common health concerns associated with hazardous waste sites (e.g., cancer, birth defects).
  
• Little information is available pertinent to the study of environmentally relevant organic compounds in hair. The panel recommended taking advantage of what is known about hair analysis for testing drugs of abuse.

In moving forward, the panelists encouraged the standardization of sampling protocols and identified possible research areas. Before hair analysis can be considered a valid tool for any particular substance, research is needed to establish better reference ranges, gain a better understanding of hair biology and pharmacokinetics, further explore possible dose-response relationships, establish whether and when hair may serve as a better measure or predictor of disease than other biological samples (e.g., blood or urine), and learn more about organic compounds in hair.

Future ATSDR Activities

ATSDR plans to evaluate all the input received during the panel deliberations and generate a report on lessons learned from the panel discussions. In addition, the agency anticipates that the following activities will help all of ATSDR's divisions as well as professionals in the community.

• Providing education to physicians and other health professionals about hair analysis.
• Developing a generic fact sheet to help health assessors and communities communicate and understand hair analysis issues.
• Continuing to develop substance-specific toxicological profiles. The profiles are an excellent resource and contain information on biomarkers of exposure. In light of the panel discussions, additional language may be added regarding hair analysis (e.g., in terms of limitations, etc.).
• Developing guidance on hair analysis to support public health assessments and health studies conducted by the agency. That is, developing criteria for determining when to consider hair analysis as part of an ATSDR exposure investigation.

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