Radioisotopic studies concerning the efficacy of standard washing procedures for the cleansing of hair before zinc analysis.

Various standard procedures were investigated in relation to the removal of exogenously applied 65Zn from human hair and endogenously incorporated 65Zn from rat hair. Human hair was found to adsorb zinc and a variety of other metal ions from aqueous solutions in a manner which suggested some ion-exchange capacity. Uptake of zinc varied considerably between human hair samples, but in most cases accumulation of zinc occurred rapidly and often resulted in hair zinc levels several-fold higher than found in control samples. Extraction of zinc and other metal ions was greatest after treatment with disodium EDTA and sodium lauryl sulfate than after washing with water or aqueous Triton X-100. However, no procedure effectively removed all exogenous zinc, while all treatments extracted varying proportions of the endogenous zinc component. Because of the inability of standard washing procedures to remove exogenous zinc without reducing endogenous or indicator zinc levels, use of hair zinc analyses to indicate nutritional zinc status are inadvisable if hair zinc contamination is likely to have occurred.