ToF-SIMS analysis of elemental distributions in human hair

Elemental distributions on whole and longitudinal sections of hairs plucked from the scalp were studied with the surface sensitive technique time-of-flight secondary ion mass spectrometry (ToF-SIMS). Endogenous and environmental influences on the distributions of elemental species were identified. The cuticle scales appear to play the major role in the accumulation of exogenous products. The functionality of the outer surfaces and scale edges each preferentially bind different elemental species. The majority of elements considered accumulated longitudinally on the outer surface of the hair above the scalp level. Internally, most elemental signals (especially Al) decreased longitudinally once exposed to the environment with the exception of Si, which showed an increase. Images of elemental distributions within the medulla suggest that regions of different reactivity exist and show a variable ability to accumulate elemental species. The greatest signal intensities were observed in the cuticle and medulla regions rather than the cortex. The cuticle is continually exposed to environmental contamination and the medulla may, or may not, exist in a hair. Therefore, the components of a hair that potentially contribute the most to the elemental concentrations (i.e. the cuticle and medulla) are also the most variable, and as such greatly complicate the interpretation of elemental concentrations in hair. Results also suggest that bleaching hair can enhance the accumulation of contaminants.