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Section 4
4.1 Distinguishing Between Endogenous and Exogenous Sources of Metals
All of the panelists agreed that using hair analysis as an exposure or diagnostic tool for metal contamination is severely limited by difficulties in distinguishing between internal and external sources of metals. It is further complicated by the natural occurrence of many of the trace elements (several of which are essential nutrients) within the body. The group recognized, however, that this distinction is not a limitation when a metabolite or a substance with no external source is being measured (e.g., organic compounds such as methyl mercury or many drugs of abuse).
Dr. Kosnett led discussions on the difficulties that exist in
distinguishing endogenous and exogenous substances in hair. Other
panelists expanded upon these issues. Individual points are summarized
below.
— Smith (1964) showed that detected concentrations of arsenic in
hair will vary depending on washing method, with no method shown
to be capable of removing all arsenic. The results of applying different
washing methods (to hair purposely externally contaminated with
12.08 ppm arsenic) are highlighted in Table 4-1. The arsenic concentration
in hair before contamination was measured at 0.14 ppm.
Table 4-1. Effect of washing method and time on arsenic levels in hair
Washing Method | Washing Time (mins) | Arsenic (ppm) |
Water | 5 | 9.16 |
15 | 5.78 | |
30 | 5.05 | |
60 | 5.03—6.21 | |
Detergent (5%) | 60 | 4.20—9.93 |
HCl (N) | 60 | 4.92—6.26 |
NaOH (N) | 60 | 0.40—0.70 |
Source: Smith 1964
— Van den Berg et al. (1968) showed similar findings. Depending
on the washing regime, this study revealed that even after 1,600
minutes of washing, externally deposited arsenic was still detected
(MK).
Measuring total concentrations in hair. Depending on the purpose of your testing, it may not be critical to distinguish between internal and external contamination. For example, in an industrial hygiene exposure investigation, identifying elevated levels of an element may be enough to suggest that the potential for exposure exists and protective measures are needed. While urine data may reveal that existing protective measures have prevented internal exposures, knowledge that employees have exposure potential may be important (e.g., contamination could be carried home) (MK, TC, MG). Several panelists reiterated, however, the limitations of using such data for clinical evaluation or interpretation.