Human hair as a noninvasive matrix to assess exposure to micro-organic contaminants: State of the art review

Human biomonitoring has played an important role in assessing human exposure to micro-organic contaminants (MOCs), including chlorinated persistent organic pollutants, brominated flame retardants, organophosphorus flame retardants, non-persistent pesticides, per- and polyfluoroalkyl substances, phthalate esters, bisphenols, and polycyclic aromatic hydrocarbons. Specifically, human hair holds great promise as a noninvasive matrix for MOC biomonitoring. While human hair has been widely used to detect numerous MOCs over recent decades, its reliability of reflecting body burden is still disputable. As a premise for discussion, it is necessary to understand the mechanisms of MOC incorporation into hair from endogenous and exogenous exposures. Then, standardized protocols must be developed to ensure accurate and reliable results. This review article discusses these issues and provides evidence for the reliability of monitoring MOCs in hair by surveying past reports from various categories of MOCs. We find that most persistent organic pollutants - especially those with a higher octanol-water partition coefficient and lower volatility - can be reliably measured using hair analysis, while internal exposure can be accurately measured using MOC metabolites in hair. Finally, we explore the applications of hair analysis in large-scale surveys, retrospective cohort studies, and epidemiological investigations, highlighting the promise of hair analysis in studying the health risks of MOCs.