2023-06-29 08:47:36
In recent years in France, several cases of unexplained cancers, particularly in children, have made the news. In Loire-Atlantique, for example, an abnormal number of leukemias had been reported between 2015 and 2019, prompting families to seize the Regional Health Agency (ARS). Health surveys had been launched to identify possible environmental factors.
Tragically, at the end of 2021 in Franconville (Val-d’Oise), little Shiloh died of a rare breast cancer at the age of 13 after a long medical wandering. Her parents are still trying to understand the origins of their daughter’s illness.
In these different cases, the question that is in everyone’s mind is: are environmental contaminations involved? Metallic and/or organic pollutants are indeed suspected of causing cancer, in particular in industrialized, agricultural or mining areas.
In addition to the actions of the national health services, are all the toxicological analysis methods reliable and accessible to families who would like to know more?
We are going to come back here to a fundamental question: the interest of hair analyses.
Metals in the hair?
In the Orbiel valley (Aude), a suspicion of exposure to arsenic after the exceptional floods of 2018 led residents to worry about the health of their children – exposure which had been confirmed by the ARS .
More recently, as families in Loire-Atlantique and Shiloh also did, residents wanted to know what their level of exposure to pollutants was.
They therefore called on a private laboratory which proposed to measure the concentrations of metals in a lock of hair by induced plasma mass spectrometry : the reference technique for the determination of metals. Hair can indeed fix metals by one of its sulfur-rich proteins, keratin, metals having a great affinity for this element.
The results of the analyzes were sent to the families in the form of tables with a long list of more or less toxic metals, their total concentrations in the hair and a color code (green, orange, red) to indicate whether the concentration was low, medium or high. The physical and chemical forms of these metals, on which their toxicity depends, were not analysed. All without medical explanation.
In this long list, cases of concentrations above the displayed thresholds could legitimately create anxiety in the people concerned, even if the laboratories offered a support service in the event of high doses.
Was such a procedure relevant? Not necessarily… Because if hair can be a good marker of contamination for certain elements, this is not the case for all metals as we will explain.
A metal present on the surface or in depth?
There are three main routes of metal contamination: by skin contact, by inhalation (after passing through the lungs), and by ingestion (food, and for children, hand-to-mouth exposure). We then speak of absorption, and it testifies to the presence of metals inside the hair.
Certain ingested or inhaled metals can, depending on their chemical form and after different processes, pass into the blood. From there, they will, in part, end up in the appendages – including the hair – by binding to cysteine, a constituent of keratin. At the level of the hair follicle, they will be integrated into the growing hair fiber. This process is one of the natural ways of eliminating certain metals from the body.
For example, the presence of methylmercury, a neurotoxic chemical species of mercury, in the hair can, depending on its concentration, be the sign of contamination because it is mainly found in food; it is in very low concentration in the atmosphere.
The other process that may explain metal concentrations in hair is adsorption, which occurs when metals in the air come into contact with it. They will also bind to the sulfur present on the surface of the fiber, but without penetrating inside. This time, the metals did not pass through the body and are not indicative of contamination by ingestion.
In some cases, the metal may be both absorbed and adsorbed. This is the case, for example, of lead emitted by various industries. The concentration of toxic metal that will be measured there will not reflect the actual contamination. Only blood tests will accurately assess lead exposure.
Metals can be simply on the surface of the hair… or integrated into its composition. The causes, and the consequences, are very different – Giovanni Cancemi/Shutterstock
The limits of hair analysis
One might think that it is enough to wash the hair to “unhook” the metals… This is only partially true. In addition, washes can be too aggressive (acid or detergent for example) and dissolve a fraction of the hair fiber.
As the chemist Steven Steindel writes (Centers for Disease Control and Prevention federal) and pathologist Peter Howanitz (Brooklyn University):
Knowing that the separation of endogenous and exogenous elements is currently difficult, if not impossible, with conventional laboratory methods, it is complicated to know what is actually measured. Until the laboratories are sure of being able to assess what has been absorbed, it is impossible to link the measurements made […] under biological conditions. (JAMA, 2001)
Hair can therefore be used to identify contamination only for metals whose exposure by ingestion is much greater than atmospheric exposure.
This is the case, for example, of arsenic, methylmercury or selenium. For these metals, a relationship can be established between the concentration in the blood and that in the hair. Doses of toxicity based on the concentration of the metal in the hair may be given.
However, very few toxicity limits based on hair analysis are currently available. This is why, in the National Institute for Research and Safety Biotox database (INRS), which takes up the proposals of the National Health Security Agency (Anses), no metal dosage is done from the hair. It is the urine or the blood that is considered, depending on the elements that one wishes to analyze.
Each metal has its own tracking method
Three metals are subject to European monitoring in food since directive 2001/22-EC. If we want to know the contamination of these metals in exposed people, this is done as follows:
Lead, with measurement of blood lead where the level of lead is analyzed in the blood (as was the case after the fire of Notre-Dame de Paris for example, or in Guyana where lead poisoning is particularly followed in children),Le cadmium, cadmiuria in the urine this time, Methylmercury, in the blood or hair if people are not exposed to atmospheric mercury. For gold panners, exposed to liquid and vapor mercury, hair analysis is not adequate and urine is analyzed.
We can therefore see that each metal has a toxicity threshold specific to the type of exposure and its chemical form. The choice of an analysis matrix (blood, hair, urine, etc.) must therefore be made on a case-by-case basis, depending on each situation.
We therefore wish warn about the use of hair as a marker of contamination. If this can give an indication of the environment in which we live, it is necessary to carry out additional analyzes to assess the actual contamination. Living in a site where one is exposed to lead does not necessarily mean contamination: only a measurement of blood lead level (in the blood) can determine it.
Moreover, the results of the analyzes of the concentrations of metals in the hair cannot, under any circumstances, be used as evidence in court. Depending on the sources of contamination, urine or blood tests are more appropriate.
This recourse to such measures, which are not adapted, testifies to the difficulty of accessing analyzes of adequate metal impregnation – which must be prescribed by a doctor. If the exposure is occupational, the occupational physician can be contacted… but it is more difficult with a general practitioner for non-occupational exposure.
It should be noted that the occurrence of usually rare diseases in several people in the same geographical area is an indicator of environmental pollution: in these cases, the ARS must be alerted to the situation. It is she who will be in charge of the medical and environmental follow-up.
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This article is produced by The Conversation and hosted by 20 Minutes.
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