Bone lead levels and delinquent behavior.
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Biomedical subjects
A C Aro
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Validation of K-XRF bone lead measurement in young adults.
K-X-ray fluorescence (K-XRF) is a useful tool for assessing environmental exposure to lead in occupationally exposed individuals and older adults. This study explores the possibility of using this technique on young adults with low environmental lead exposure. Twenty-three college students, aged 18-21 years, were recruited for 2 hr of bone lead measurement. Bone lead measurements were taken from the mid-shaft tibia for periods of 30 or 60 min. In the analysis, 30-min measurements were combined so that each subject had the equivalent of two 60-min measurements. The average concentration of two bone lead measurements in this population ranged from -1.5 to 8.2 micrograms Pb/g bone mineral, with a mean of 3.0 micrograms Pb/g bone mineral. In a one sample t-test, this mean was significantly different from 0 (p < 0.0001). A linear trend with age was detected despite the small age range of our population. By doubling the sampling time, the reported measurement uncertainty decreased by a factor of 1.5, resulting in uncertainty estimates below the mean bone lead estimates. Power calculations using the observed variance estimates suggest that with 80% power, differences in bone lead concentration of 2-3 micrograms Pb/g bone mineral can be identified in groups of 100 or smaller. Due to the large within-person variation in young adults, K-XRF may not yet be a useful diagnostic tool for individual subjects, but it may be of great use to environmental scientists trying to characterize long-term lead exposure and dose in the general population or specific subpopulations.
Adolescent↗
Improvements in the calibration of 109Cd K x-ray fluorescence systems for measuring bone lead in vivo.
A 109Cd K x-ray fluorescence (XRF) system using a point source in a back-scatter geometry is described. The suitability of plaster-of-Paris phantoms as targets for intercalibration standards was evaluated. When the phantom concentrations were measured by inductively-coupled-plasma mass spectrometry (ICPMs), the calculated phantom concentrations underestimated true concentrations by an average of 15%. Since calculated values are used to calibrate the K XRF system, in vivo bone-lead concentrations may be similarly underestimated. The difference between calculated and measured concentration is attributable to impurities in the plaster of Paris (e.g. calcium carbonate). The ICPMS-measured concentrations were used to calibrate the K XRF system. The same phantoms were also measured as 'unknowns' by a bone-lead measurement system (Abiomed, Danvers, MA, USA). The commercial system overestimated the lowest-concentration phantoms and underestimated the phantoms with concentrations above 15 microg Pb/g plaster of Paris. The commercial system and our system were compared by measurement of the new phantoms in air and in water. The K XRF system exhibited better precision in both situations. On the basis of this work, we recommend that plaster-of-Paris phantoms used to calibrate K XRF measurement systems be analysed first by ICPMS or another valid analytical technique.
Bone and Bones↗