A chemist's view of the analysis of human hair for trace elements

With the comparatively recent development of analytical techniques of great power and sensitivity, the significance of the levels of trace elements in human hair has attracted the attention of many disciplines including the environmental sciences. This paper presents the view that an agreed basis for the chemical analysis of trace elements in hair has not been established by the many workers in the field; a chemical basis is proposed here. Levels of 37 trace elements found in human hair are tabulated. Endogenous and exogenous sources of such trace elements are described and discussed. An extended review of the many pre-analysis treatments of hair (for the removal of exogenous elements) is presented. Twenty-four representative treatments are tabulated. Some of these treatments clearly removed significant fractions of endogenous elements along with exogenous elements. It is clear that method of cleaning have frequently been chosen without knowing enough about the basic chemistry and behaviour of the hair shaft. The significance of the results obtained cannot therefore be reliably assessed. A collation of recent literature reports leads to the tentative conclusion that disulphide bonds in the cuticular proteins of hair are major sites both for the deposition of metals during formation of hair and for interaction with exogenous elements. The feasibility of a holistic, no-wash policy for hair analysis is outlined and supported.