METALS IN HAIR AS BIOLOGICAL INDEXES FOR EXPOSURE

Hair samples from three groups of occupationally exposed subjects were analyzed for their lead (Pb), manganese (Mn) and mercury (Hg) contents. For lead (number of subjects, n=209), the hair Pb ranged from 0.93 to 3527 mug/g (geometric mean, GM=641) and blood Pb from 33.3 to 774 mug/l (GM=341); for manganese (n=38), the hair Mn ranged from 0.20 to 52.97 mug/g (GM=2.66) and urine Mn ranged from 1.70 to 17.9 mug/l (GM=5.56); and for mercury (n=85), the hair Hg from 1.79 to 12.8 mug/g (GM=5.09) and the blood Hg from 0.63 to 57.3 mug/l (GM=10.9). The hair Pb was significantly (P<0.0001) correlated to blood Pb (r=0.85); the hair Mn to urinary Mn (r=0.45); and the hair Hg to blood Hg (r=0.53). The average metal content at the distal end was not significantly (P>0.05) different from that of proximal end. The GM levels for the distal end were 223 mug/g (95% CI 152-347) and 2.26 (95% CI 0.97-5.29); and those for the proximal end were 186 (95% CI 97-261) and 1.18 (95% CI 0.54-2.58) for Pb and Mn respectively. However, linear regression analysis of hair metal levels in the proximal end with respect to those in the distal end after logarithmic transformation showed that hair Pb in the proximal end was related to hair Pb in the distal end with a slope of 0.95 (95% CI 0.89-1.01) whereas hair Mn in the proximal end was related to that of the distal end with a slope of only 0.52 (95% CI 0.13-0.91), reflecting the relatively constant Pb exposure as compared to the dropping Mn exposure in recent years. Metals in hair are suitable biological indicators for exposure and the distribution along the different segments of hair strands reflects the time history of exposure.