Impact of Occupational Exposure on Lead Levels in Women
Impact of Occupational Exposure on Lead Levels in Women
In 1994, 207 women participated in a study designed to examine the effects of occupational exposure and various lifestyle factors on bone and blood lead levels. In vivo measurements of Pb concentrations in tibia were performed by X-ray fluorescence. All 108 former smelter employees and 99 referents provided blood samples and answered a questionnaire on lifestyle characteristics and the relevant medical history. Lead concentrations in tibia and blood were significantly higher in the exposed group. The difference in mean bone Pb concentrations of the two groups is markedly greater than the difference in the mean blood Pb concentrations, supporting the view that bone Pb measurements are a more reliable determinant of Pb body burden. Chronic exposure did not result in any statistically significant differences in adverse pregnancy outcomes. A significantly lower age at the onset of menopause in occupationally exposed women may suggest that Pb causes adverse changes in the pattern of estrus and menses. The exposed women had lower bone Pb concentrations than those found in most studies on predominantly male workers. Blood Pb concentrations remain increased in women long after the cessation of occupational exposure, reflecting the importance of the endogenous exposure. The endogenous exposure relation found for postmenopausal exposed women is consistent with data on male smelter workers, whereas the relation found for premenopausal women is significantly lower. This suggests that sex plays an important role in the metabolism of lead, and current models of exposure extrapolated from male data may be inappropriate for use on women. Key words: blood lead concentration, bone lead concentration, lead, occupational exposure, women's health, X-ray fluorescence. Environ Health Perspect 113: 478-484(2005). doi:10.1289/ehp.7386 available via http://dx.doi.org/ [Online 9 February 2005]
The mobilization of endogenously stored lead represents an important health threat to individuals who have experienced elevated exposure in the past. From the skeleton as a primary storage site, lead gradually reenters the circulation through bone resorption. Endogenous exposure may be increased during phases of physiologic stress that are accompanied by elevated bone resorption. Various manifestations of Pb toxicity have been uncovered through epidemiologic investigations [World Health Organization (WHO) 1995]. Among the most harmful are its effects on the developing central nervous system of fetuses and children.
Calcium demands of the fetus and breast-fed infants are partially met through an increase in maternal bone turnover. Skeletal Pb is concurrently mobilized due to the similarities of the atomic and ionic structures of Pb and calcium. Maternal bone Pb levels are directly correlated with infant blood levels and umbilical cord levels of Pb (Hernandez-Avila et al. 2002; Sanin et al. 2001). In addition, the disturbance of skeletal homeostasis associated with menopause can result in a greater transfer of Pb from bone to the bloodstream. Although healthy men experience relatively constant life-long bone Pb accumulation with chronic exposure, exaggerated endogenous release is expected to occur in women with each pregnancy, throughout lactation, and during menopause.
The aim of this analysis was to uncover the differences between sexes in Pb metabolism. Cohorts of environmentally and occupationally exposed women were compared with regard to various medical and lifestyle factors, providing a degree of adjustment for confounders and more accurate identification of effects related to Pb exposure. Female former workers at the Bunker Hill smelter in Idaho were then compared with other, predominantly male, cohorts to investigate potential sex hormone-driven differences in the long-term skeletal accumulation of lead.
In 1994, 207 women participated in a study designed to examine the effects of occupational exposure and various lifestyle factors on bone and blood lead levels. In vivo measurements of Pb concentrations in tibia were performed by X-ray fluorescence. All 108 former smelter employees and 99 referents provided blood samples and answered a questionnaire on lifestyle characteristics and the relevant medical history. Lead concentrations in tibia and blood were significantly higher in the exposed group. The difference in mean bone Pb concentrations of the two groups is markedly greater than the difference in the mean blood Pb concentrations, supporting the view that bone Pb measurements are a more reliable determinant of Pb body burden. Chronic exposure did not result in any statistically significant differences in adverse pregnancy outcomes. A significantly lower age at the onset of menopause in occupationally exposed women may suggest that Pb causes adverse changes in the pattern of estrus and menses. The exposed women had lower bone Pb concentrations than those found in most studies on predominantly male workers. Blood Pb concentrations remain increased in women long after the cessation of occupational exposure, reflecting the importance of the endogenous exposure. The endogenous exposure relation found for postmenopausal exposed women is consistent with data on male smelter workers, whereas the relation found for premenopausal women is significantly lower. This suggests that sex plays an important role in the metabolism of lead, and current models of exposure extrapolated from male data may be inappropriate for use on women. Key words: blood lead concentration, bone lead concentration, lead, occupational exposure, women's health, X-ray fluorescence. Environ Health Perspect 113: 478-484(2005). doi:10.1289/ehp.7386 available via http://dx.doi.org/ [Online 9 February 2005]
The mobilization of endogenously stored lead represents an important health threat to individuals who have experienced elevated exposure in the past. From the skeleton as a primary storage site, lead gradually reenters the circulation through bone resorption. Endogenous exposure may be increased during phases of physiologic stress that are accompanied by elevated bone resorption. Various manifestations of Pb toxicity have been uncovered through epidemiologic investigations [World Health Organization (WHO) 1995]. Among the most harmful are its effects on the developing central nervous system of fetuses and children.
Calcium demands of the fetus and breast-fed infants are partially met through an increase in maternal bone turnover. Skeletal Pb is concurrently mobilized due to the similarities of the atomic and ionic structures of Pb and calcium. Maternal bone Pb levels are directly correlated with infant blood levels and umbilical cord levels of Pb (Hernandez-Avila et al. 2002; Sanin et al. 2001). In addition, the disturbance of skeletal homeostasis associated with menopause can result in a greater transfer of Pb from bone to the bloodstream. Although healthy men experience relatively constant life-long bone Pb accumulation with chronic exposure, exaggerated endogenous release is expected to occur in women with each pregnancy, throughout lactation, and during menopause.
The aim of this analysis was to uncover the differences between sexes in Pb metabolism. Cohorts of environmentally and occupationally exposed women were compared with regard to various medical and lifestyle factors, providing a degree of adjustment for confounders and more accurate identification of effects related to Pb exposure. Female former workers at the Bunker Hill smelter in Idaho were then compared with other, predominantly male, cohorts to investigate potential sex hormone-driven differences in the long-term skeletal accumulation of lead.
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