Hair Analysis Panel Discussion: Section 3.3
Error processing SSI fileSection 3
3.3 Analytical Methods
The group noted that reliable analytical methodologies do exist to measure and verify the presence of various substances in hair. Several panelists specified methods currently used for hair analysis in their pre-meeting comments; throughout the meeting, they mentioned some of the methods' strengths and weaknesses, as well as their applicability. This section highlights the points made during the meeting, but should not be considered an exhaustive discussion of existing methodologies. The methods discussed include:
Cold Vapor Atomic Absorption (AA). It was noted
that this is the preferred methodology for measuring methyl
mercury.
Inductively Coupled Argon Plasma Mass Spectrometry
(ICP-MS). ICP-MS has widespread use in commercial laboratories.
It can be used to measure methyl mercury, but it is difficult
to get reproducible calibrations (DP). With certain types
of mass spectrometry, stable isotope studies can help show
the incorporation rates of certain elements in hair, which
may help to answer some of the toxicology questions. For
example, a 20-day delay has been shown between the appearance
of lead in blood and its appearance in hair (TC).
Inductively Coupled Argon Plasma Optical Emission
Spectrometry (ICP-OES) or Inductively Coupled Argon Plasma
Atomic Emission Spectrometry (ICP-AES). Of the commonly
used methods, ICP-OES/AES is used the most (DP). This method
makes it possible to generate a large amount of data on
a large number of elements. It is a "quick and dirty" way
of getting a global picture of the elemental composition
of a hair sample.
It was noted that, historically, CDC used Jarrell Ash Model
1160 AtomComp (e.g., to generate the data cited in DiPietro
et al. 1989). CDC presently uses a Jobin Yvon Ultima C (DP).
Neutron Activation Analysis (NAA). NAA has been
used in forensics to measure trace elements in small quantities
of hair. It can be used for segmental analysis of hair.
Segmental analysis can reveal isolated elevations of contamination
along the hair and provide information regarding the contamination
of the length of the hair over time. Identifying patterns
over time can help distinguish whether exposure is endogenous
or exogenous (see also Section 4).
These techniques are not widely commercially available,
however (MK).
X-ray Fluorescence. This technique is amenable,
nondestructive, and multi-element. It also has the advantage
of measuring the mass of hair as well as the amount of the
element present in that segment of hair (TC). Another panelist
noted that the distribution of mercury in segments along
the length of a single strand of hair may be determined
by x-ray fluorescence.
Proton Induced X-ray Emission (PIXE) Spectrometry. This method was brought into play approximately 30 years ago. This method studies a cross section of hair, enabling identification of external versus internal contamination. This method has not been used very much because the instrument is expensive (TC). One panelist noted that single-strand analysis can be problematic if hair is in the non-growing phase (RB), although it was noted that this is not a problem if the sample is taken from the root (TC).
Another panelist commented on the variable success of the PIXE method. For example, differentiating internal and external arsenic may not always be that straightforward. In cases of internal uptake, peaks of arsenic on the external shaft of hair may be a consequence of appreciable cysteine residues and sulphydral groups. In cases of external contamination, washing procedures may lead to greater incorporation of external contamination into the shaft (MK).
Given the various methodologies that might be used, several panelists pointed out the importance of understanding the method and analytical equipment used when interpreting hair analysis results, noting that it is the laboratory's responsibility to clearly report the method used, quality assurance measures taken, any possible interferences, etc. Further, the data user should carefully consider this information when evaluating the results.
As stated by one panelist, it is easy to standardize measurements by using good standards and good laboratory practice (use of blanks, use of external verification) (DP). While the group recognized that valid methods exist, several panelists stressed that the challenge lies in the interpretation (see Section 4 of this report)
