Lead concentrations in human tissues.

339-351. A study of 69 subjects at post-mortem, four of whom had histories of occupational exposure to lead, demonstrated a marked difference in the lead concentrations between bones and soft tissues. The soft tissues of infants and young children contained low concentrations of lead, varying from 0·01 ppm in muscle to 0·46 ppm in liver. By the end of the second decade of life the concentrations of lead in most of the soft tissues showed values varying between 0·06 ppm in muscle and 1·35 ppm in liver and thereafter did not increase with advancing age. The concentrations of lead in bone were considerably greater than those in soft tissues, being about 1 ppm in infants and young children and increasing to more than 40 ppm in persons over the age of 50 years. Adult male bones contained more lead than adult females by a ratio of 3 to 2, and in both sexes the long bone contained concentrations of lead two and a half times that observed in the flat bone. No marked difference was noted in lead concentrations between the corresponding soft tissues of the two sexes. From the findings it appeared that in adults the total body burden varied widely from subject to subject. Nearly 95% was represented by the lead content in bone, of which more than 70% was in dense bone. A far lower concentration of lead was found in the bones of children than in those of adults, but there was less divergence in the lead concentrations in the soft tissues. The total lead content in the soft tissues of the majority of the subjects investigated appeared to be relatively stable and did not correlate with levels in bone. The four male subjects with known occupational exposure to lead had greater concentrations of lead in bone than those with no known occupational exposure, but no difference was noted in the soft tissues between the two groups, with the exception of the most heavily exposed subject in whom concentrations of lead in the brain were over 4 ppm and in the aorta 28 ppm. Hair and nails were found to contain relatively high concentrations of lead, approximately 20 ppm; some significance may be attached to this finding in a medico-legal context. The findings of this study would suggest that the present intake of lead among the general population is no greater than in the past.