Academic journal article Environmental Health Perspectives

Individual Variability in Human Tibia Lead Concentration. (Articles)

Academic journal article Environmental Health Perspectives

Individual Variability in Human Tibia Lead Concentration. (Articles)

Article excerpt

Our aims in this study were to determine proximal-distal variability in adult human tibia lead concentration via electrothermal atomization atomic absorption spectrometry (ETAAS) and to determine whether there were any differences between core and surface tibia lead concentrations. We analyzed duplicate core and surface tibia samples for lead at multiple proximal-distal sections on 10 adult human cadaver legs. Dried bone samples were digested in nitric acid using microwave-assisted heating, and lead content was determined by ETAAS with Zeeman background correction. Lead concentrations in nine tibiae (one tibia was excluded because some of the data were compromised) ranged from 3.1 to 27.9 [micro]g lead/g of dry bone. Both core and surface tibia lead concentrations were lower at the proximal and distal ends of the tibia. Surface tibia lead was approximately 5 [micro]g/g greater than core tibia lead in six tibiae with relatively low lead concentration, and 8 [micro]g/g greater in three tibiae with relatively high lead concentration. The difference between core and surface tibia lead was independent of proximal-distal tibia location. We conclude that these nine human tibiae showed a greater surface tibia lead concentration than core tibia lead concentration. This observation has consequences for the noninvasive measurement of tibia lead via K-shell and L-shell X-ray fluorescence. Key words. atomic absorption spectrometry, bone lead, lead poisoning. Environ Health Perspect 109:1139-1143 (2001). [Online 23 October 2001] http://ehpnet1.niehs.nih.gov/docs/2001/109p1139-1143todd/abstract.html

Environmental and occupational exposures to lead continue to be widespread public health concerns and the subjects of much study. Exposure to lead is usually assessed by the measurement of lead in whole blood, but blood lead reflects only recent exposure because the biological residence time of lead in blood is approximately 1 month (1). The body's largest repository for lead is the skeleton (2,3), wherein the residence time of lead is of the order of years (1,4); thus bone lead is a good surrogate for lifetime exposure (5).

There are few studies of the distribution of lead in the human skeleton using instrumental analytical methods, such as electrothermal atomization atomic absorption spectrometry (ETAAS). Wittmers et al. (6) measured lead concentrations in several human bones, including the tibia, from 134 hospital autopsies. They found no linear relationship between bone lead concentration and the location along the diaphysis. The authors reported bone lead concentrations in micrograms per gram of ashed bone because sample pretreatment included a dry-ashing step in which bone material was oxidized to ash using a muffle furnace. Parsons et al. (7) reported lead concentrations in the long bones of lead-dosed animals. They found no clear trend in lead distribution along a single 20-cm bovine tibia. The bone lead data of Parsons et al. (7) were reported in micrograms per gram dry weight because dried bone material was digested (wet ashed) in concentrated nitric acid. Conversion of bone lead concentrations based on ash weight into concentrations based on dry weight requires data on the percentage of ash in a given sample. Zong (8) reported detailed measurements of lead-dosed goats and found that the lead concentration in some goat tibiae increased toward the proximal and distal ends of the tibia. However, no consistent pattern was found in the few animals studied. One aim of our study was to determine whether adult human tibiae yielded more consistent observations.

Bone can be broadly divided into two types: cortical and trabecular. The mid-shafts (diaphyses) of long bones tend to be predominantly cortical or compact, while the ends (epiphyses) are characteristically more trabecular or spongy. The percentage by mass of calcium is less in trabecular bone than that in cortical bone (9). Lead in bone can be measured noninvasively and in vivo using [sup. …

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