Longitudinal changes in bone lead concentration: implications for modelling of human bone lead metabolism

Abstract

In this study, 539 occupationally exposed subjects received in vivo bone lead measurements using 109Cd excited K X-ray fluorescence (109Cd K XRF). Of these subjects, 327 had previously been measured five years earlier. Measurements were made from both tibia and calcaneus samples, taken to reflect cortical and trabecular bone, respectively. Changes in tibia lead concentration related negatively to initial tibia lead concentration and positively to both lead exposure between the measurement dates and initial calcaneus lead concentration. This finding confirmed and strengthened the interpretation of an earlier study involving fewer subjects. With the larger data set it was possible to examine subgroups of subjects. This showed that people aged less than 40 years had a shorter half-life for the release of lead from the tibia (4.9, 95% CI 3.6-7.8 years) than did those older than 40 (13.8, 95% CI 9.7-23.8 years). Similarly, less intensely exposed subjects (lifetime average blood lead < or = 25 micrograms dL-1) had a shorter tibia lead half-life (6.2, 95% CI 4.7-9.0 years) than those with a lifetime average blood lead > 25 micrograms dL-1 (14.7, 95% CI 9.7-29.9 years). Age and measures of lead exposure were strongly correlated; nevertheless, age matched subgroups with high and low intensity exposures showed clearance rates that were significantly different at the 10% level, with the lower exposure intensity again being associated with the faster clearance. These findings imply that current models of human lead metabolism should be examined with a view to adjusting them to account for kinetic rates varying with age and probably also with exposure level.

Changes in bone Pb accumulation: Cause and effect of altered bone turnover

“…As a matter of fact, if only the estimated contrasts in bone resorption between actually exposed groups in this study were considered, then the current results would suggest that decreasing OC levels favor the increment of the halflife of Pb in bone with increasing exposure. This is consistent with the conclusion that the half-life of Pb in bone is increased at higher exposure, established in previous work based on a sample 75% of which were Pb exposed subjects older than 40 years [8], and therefore with OC expectedly at the lowest levels according to published data [42]. As a final remark, such consistency is not undermined by the lack of statistical significance of the estimated contrasts in bone resorption between exposed groups in this work , 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 because even with a much larger sample not all half-life contrasts for compact and trabecular bone reach the traditional 5% level of significance [8].…”

“…In view of current assumptions in PBKM, namely that Pb is incorporated in bone during bone formation and is removed from bone during bone resorption [3,4], it seems paradoxical that both osteopenia and increased half-life of Pb in bone, as suggested in this work and observed in previous studies [7,8], respectively, are apparently associated with higher exposures to Pb. This apparent paradox, however, can be explained by the methodological options of data analysis followed in this and previous studies.…”

“…The same authors report also that consistency between the model predictions and the data for trabecular bone was not achieved even after the corresponding default transfer rate from bone to plasma was reduced by a factor of 4. Moreover, data from a repeat bone Pb survey performed with occupationally exposed subjects showed that people aged less than 40 years have shorter half-life for Pb in tibia than did those older than 40, and that less intensely exposed subjects have shorter tibia Pb half-life than those with higher exposure [7,8]. In an independent approach to the transfer of Pb between body compartments, the earlier observation of the age-and exposure dependence of the transfer rate of Pb from bone to blood was confirmed and refined [9].…”

Atomic spectrometry update. Clinical and biological materials, foods and beverages

“…51,52 Following improvements in industrial hygiene, tibia Pb concentrations in 51 subjects had fallen to a mean of 33 mg g bone mineral 21 from a mean of 39 mg g bone mineral 21 in a previous study five years earlier. However, surprisingly, calcaneous Pb had not fallen significantly from a level of 64 mg g bone mineral 21 .…”

Using Ionizing Radiation to Determine Trace Element Content in Living Human Subjects

“…It was found that subjects with higher bone Pb had significantly slower release rates of Pb from bone. When a different comparison was made within the overall group, it was found that older subjects released Pb from bone more slowly than did younger people 33) . Within this overall study, as within nearly all similar groups, bone Pb correlates strongly with age for two reasons.…”