Application in Forensics (Mercury)
As hair is a “growing” tissue, and once formed is metabolically inert, it can record toxic metal exposure over time (i.e., what is happening in your blood). The period of time where we can go back depends on the length of the hair; essentially about 1 cm of hair length equals 1 month of growth. This approach cannot be conducted on all metals due to the propensity for external contamination once the hair leaves the scalp. However, mercury is a fantastic candidate for this type of analysis.
Above is an example of a consultant that went onto a work site in mid-July of 2016 and believed he was exposed to mercury, but did not get assessed until January 2017. Unfortunately, by this time diagnostic tools such as blood and urine, could not monitor an exposure event from 6 months previous. Using a single hair we were able to date his exposure event to end of July 2016 (his total time on site is indicated in yellow shading). This was determined to be an acute exposure due to the significant increase in mercury concentration that would not be possible from a dietary source, which would show a more gradual increase. The decreasing trend after the exposure event indicates that it took approximately 4 months for the mercury concentrations to return to baseline levels.