In vivo tibia lead measurements as an index of cumulative exposure in occupationally exposed subjects.

Abstract

In vivo tibia lead measurements of 20 non-occupationally exposed and 190 occupationally exposed people drawn from three factories were made using a non-invasive x ray fluorescence technique in which characteristic x rays from lead are excited by gamma rays from a cadmium-109 source. The maximum skin dose to a small region of the shin was 0-45 mSv. The relation between tibia lead and blood lead was weak in workers from one factory (r = 0 11, p > 0.6) and among the non-occupationally exposed subjects (r = 0 07, p > 0 7); however, a stronger relation was observed in the other two factories (r = 0 45, p < 0 0001 and r = 0 53, p < 0-0001). Correlation coefficients between tibia lead and duration of employment were consistently higher at all three factories respectively (r = 0-86, p < 0-0001; r = 0-61, p < 0-0001; r = 0 80, p < 0 0001). A strong relation was observed between tibia lead and a simple, time integrated, blood lead index among workers from the two factories from which blood lead histories were available. The regression equation from two groups of workers (n = 88, 79) did not significantly differ despite different exposure conditions. The correlation coefficient for the combined data set (n = 167) was 0-84 (p < 0-0001). This shows clearly that tibia lead, measured in vivo by x ray fluorescence, provides a good indicator of long term exposure to lead as assessed by a cumulative blood lead index.As a consequence of the well established toxicity of lead, workers occupationally exposed to it in the United Kingdom and other industrialised countries are subjected to regular monitoring of blood lead concentrations. In In vivo tibia lead measurements as an index ofcumulative exposure in occupationally exposed subjects is relatively stable, as with the tibia, it is feasible to normalise per mass of wet bone. The relation between wet bone mass and bone mineral in trabecular bone, however, is less well defined and changes with, among other things, age, particularly in women. Because our technique normalises to the gamma rays coherently scattered from both calcium and phosphorus, the most logical normalisation is therefore to the bone mineral mass. This is equivalent to quoting the lead content per mass of bone ash, a unit that is widely used for in vitro analysis. A possible alternative, particularly for those making biopsy measurements using atomic absorption spectrometry, is to normalise to the calcium content: however, the relation between the two procedures is readily established assuming bone mineral to consist of calcium hydroxyapatite (Ca10(P04)6(OH)2). As our measurement programme is being extended to include trabecular bone we have therefore chosen to normalise to bone mineral mass throughout.x Ray fluorescence, which involves stimulation of characteristic x ray emission from the element of interest using a beam of photons, has been used by several groups to measure bone lead. The first to do so were Ahlgren and co-workers,45 who measured the lead K. x ray emission (at 75 0 and 72-8 keV for K., and...

Current issues in the epidemiology and toxicology of occupational exposure to lead.

“…For evaluation of these effects a marker of chronic absorption is needed. A most promising approach to development of such a measure is offered by X-ray fluorescence analysis, a technology that permits rapid, noninvasive assessment of the lead burden in bone (51)(52)(53). Application of this technology in epidemiologic studies which also use newly developed biological markers of subclinical impairment offers the possibility of reliable early detection of lead-induced nephropathy in lead workers who are not yet clinically impaired.…”

“…Again, the most promising approach to this measure appears to be noninvasive X-ray fluorescence analysis of lead in bone (51,53).…”

Individual Variability in Human Tibia Lead Concentration

“…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).…”

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

“…It was quickly demonstrated that bone Pb correlates with age in subjects not occupationally exposed, with years of work in occupationally exposed people and only more weakly with current blood Pb in those same Pb workers. By far the strongest of these correlations, however, is with a Cumulative Blood Lead Index (CBLI) 27) . CBLI is the area under the curve when whole blood Pb is plotted against time.…”