Coverage intervals for trace elements in human scalp hair are site and also gender-specific

Hair analysis is a powerful tool for assessing human exposure to metals and metalloids (MM). The basis forinterpreting laboratory results lie on the use of coverage intervals (CI), computed between the 0.025 and 0.975 fractiles,from a well-defined group of reference individuals reflecting normal and healthy people.A critical point in efficient use of CI, when used for comparative decision-making processes, forensic and clinicconsiderations, is constituted by confounding factors as the specific living site of study population and gender ofparticipants. Our study aims to demonstrate that hair levels of trace elements are site specific and also gender specific.We have taken into account the levels of 20 trace elements in hair samples from children of the same age (11-14years old) residing in Sicilian sites characterized by different environmental conditions. The dataset consisted of hairsamples collected within the urban area of Palermo, in several small towns located around the volcanic area of Mt. Etnaand close to the industrial area of Gela.The study was organized as follow: (a) the first part was addressed to establish whether coverage intervals for MMin human scalp hair are to be considered site specific reflecting local environmental conditions; (b) the second part wasintended to provide more information about the gender effect on MM distribution in human scalp hair.The obtained main results can be summarized as follows:a) for many elements, the computed CIs are clearly not equivalent for the different sites, but rather the interval ofan element for a site extends far beyond that one calculated for another site, suggesting that what is normal for one sitemay not be normal for another site. Therefore CIs are valid only for a well defined area and can hardly be extended toother areas with different characteristics.b) CIs of several elements computed for hair samples from female subjects are statistically different from thosecomputed for male subjects. For example, Cd, Li and Rb male coverage intervals extend far beyond those calculated forfemales, instead, those of Cu, Mn, Ni, Sr, V and Zn are wider for females than males. The Mann-Whitney test (p <0.01) showed statistically significative differences, between males and females, for Al, Ba, Cd, Co, Cr, Cu, Mn, Ni, Pb,Rb, Sb, Se, Sr, V and Zn. Linear Discriminant Analysis indicated a clear-cut separation in terms of Sr, Ni, Zn, V, Cd,Cu, Mn, Mo and Pb levels for females and Se, Cr, As, Li, Rb and Sb levels for males. We have concluded that CIcomputed for human hair are to be considered gender specific and they reflect the different basal metabolism betweenboys and girls.Therefore, the levels of trace elements in hair cannot strictly comparable between different areas and betweensubjects of different sex. This issue is particularly relevant when identification of anomalous (peculiar) environmentalexposures are requested or even in detecting physiological disorders.