External Contamination in HTMA: Sources, Risks and Laboratory Mitigation

Why contamination matters in HTMA

Hair is continuously exposed to the external environment. Minerals and metals may accumulate not only through endogenous incorporation during hair growth, but also from environmental contact after the hair emerges from the scalp.

Potential contamination may affect interpretation of:

• toxic metals,
• trace elements,
• mineral ratios,
• longitudinal comparisons.

For this reason, pre-analytical handling and laboratory methodology are critically important.

Common sources of external contamination

• shampoos and conditioners,
• hair dyes and bleaching agents,
• swimming pool exposure,
• hard water minerals,
• occupational exposure,
• environmental dust and pollution,
• cosmetic sprays and styling products,
• metallic workplace particles,
• cigarette smoke.

Some elements such as aluminum, lead and mercury may be particularly vulnerable to external deposition, which can complicate the distinction between endogenous incorporation and surface contamination.

Hair washing protocols in laboratories

Before elemental analysis, laboratories typically apply standardized washing procedures intended to reduce surface contamination.

Common approaches include:

• non-ionic detergents,
• acetone washes,
• deionized water rinsing,
• multi-step cleaning protocols.

However, no universal protocol exists across all laboratories.

Different washing methods may:

• remove contaminants,
• partially remove endogenous minerals,
• influence reproducibility between laboratories.

ICP-OES and contamination control

Modern HTMA laboratories commonly use ICP-OES or ICP-MS instrumentation for elemental measurement.

Analytical precision of the instrument itself does not eliminate pre-analytical variability.

Laboratory quality depends on:

• standardized sample preparation,
• contamination control,
• calibration,
• reference materials,
• reproducibility testing.

Hair dyes and cosmetic treatment

Can dyed hair still be analyzed?

Hair coloring and chemical treatment may alter elemental concentrations depending on:

• dye composition,
• bleaching intensity,
• frequency of treatment,
• analyzed element.

Some laboratories still accept treated hair with caution, while others recommend untreated samples whenever possible. Neutral interpretation is essential.

Scientific debate and reproducibility

Scientific literature on HTMA reproducibility remains mixed.

Some studies report:

• acceptable reproducibility under controlled conditions,
• utility in exposure assessment,
• long-term trend observation.

Other publications highlight:

• variability between commercial laboratories,
• lack of methodological standardization,
• inconsistent interpretation models.

This remains an active methodological discussion within the field.

How contamination risk can be reduced

• collect hair close to the scalp,
• avoid recently dyed hair if possible,
• use clean stainless steel scissors,
• avoid styling products before sampling,
• follow laboratory collection instructions carefully,
• use consistent laboratories for longitudinal comparison.

Conclusion

External contamination is a genuine limitation of HTMA and should always be considered during interpretation.

Laboratory preparation methods can reduce contamination risk, but they cannot completely eliminate all pre-analytical variability.

Responsible interpretation requires:

• awareness of methodology,
• standardized collection procedures,
• understanding of laboratory limitations,
• cautious scientific interpretation.

HTMA should therefore be viewed as a contextual analytical tool rather than a standalone diagnostic method.

Frequently Asked Questions

References

1. Seidel S et al. Assessment of commercial laboratories performing hair mineral analysis. JAMA.
2. Kempson IM, Lombi E. Hair analysis as a biomonitor for toxicology, disease and health status. Chemical Society Reviews.
3. Eastman RR et al. Hair as a biomarker of environmental manganese exposure. Environmental Science & Technology.
4. World Health Organization. Environmental Health Criteria: Trace Elements in Human Hair.
5. Mikulewicz M et al. The comparison of hair and serum trace element concentrations.