Hair as a “witness” to exposure to fast-elimination chemicals

• Department of Precision Health
• Human Biomonitoring Research Unit

Hair analysis can be a good way of monitoring exposure to chemicals that are rapidly eliminated from the body. This has been demonstrated by a study conducted by the French National Health and Safety Agency (l’Agence nationale de sécurité sanitaire – ANSES), the Luxembourg Institute of Health and the French National Institute for the Industrial Environment and Risks (l’Institut national de l’environnement industriel et des risques – Ineris). This work has specified for which molecules this analysis is most relevant.

Bisphenols, phthalates and pesticides are some of the chemical substances to which we are exposed through our environment or food but are eliminated by our bodies in just a few hours. Coupled with frequent re-exposure, this can be an obstacle to assessing long-term exposure to them using blood or urine analyses. “We were confronted with this problem during a study on bisphenol A”, explains Claire Beausoleil, toxicologist within the ANSES Risk Assessment Department. Indeed, the results of several scientific studies concluded that there was no correlation between the effects studied in humans and the concentrations of bisphenol A measured in urine. Could this mean that the people studied had not been exposed to doses high enough to be detected in their urine? Or does it mean that the measurements did not adequately reflect exposure, mainly because the substance was eliminated too quickly, resulting in a high variability in urinary concentration? It is therefore essential to be able to trace internal exposure to a chemical substance in order to identify its long-term toxicity. Indeed, the health effects of a substance depend on its concentration within the body.

To find out which analysis method is the most appropriate for a given substance, the Anses, the LIH and the Ineris designed a dedicated study. The scientists wanted to know whether it was possible to use hair to measure exposure to certain pollutants, as hair sampling is simpler than blood or urine sampling and could better reflect the actual exposure of individuals.

Rats, used as models, were exposed by ingestion to a mixture of 17 pollutants, namely pesticides, phthalates, bisphenols and another plasticiser, DINCH. Hair and urine samples were then collected to measure the concentrations of metabolites produced by the transformation of these substances in the body.

The team found that, for 14 of the 17 substances to which the animals had been exposed, there was a good correlation between the dose of exposure by ingestion and the concentration of metabolites measured in the hair. This concentration was also proportional to that found in the urine, indicating that the substances had built up in the hair after being transported by the blood. 

For substances whose concentration in the hair is a good reflection of actual exposure, this measurement may even be more representative than blood analysis. This is because the substance may have been eliminated from the blood by the time the sample is collected, whereas hair retains traces of the pollutant for longer once it has attached itself to the keratin. Hair analysis reflects exposure over a longer period and is not subject to the short-term variations usually measured in blood or urine.

The incorporation of substances into hair depends on parameters such as the time taken for the molecules to be absorbed and eliminated. These parameters vary from one species to another. In order to extrapolate the data from the rat study to humans, a further adjustment is required to take account of the metabolic specificities of the two species.

The full study can be accessed here.