In Vivo X-ray Fluorescence of Lead and Other Toxic Trace Elements

Abstract

The first in vivo x-ray fluorescence measurements of lead in bone used y-rays from a {sup 57}Co source to excite Pb K x-rays. Later systems used {gamma}-rays from {sup 109}Cd to excite Pb K x-rays or polarized x-rays to excite Ph L x-rays. All three approaches involve an extremely low effective dose to the subject. Of the two K x-ray techniques, {sup 109}Cd is more precise and more flexible in choice of measurement site. Pb L x-ray fluorescence (L-XRF) effectively samples lead at bone surfaces, whereas Ph K x-ray fluorescence (K-XRF) samples through the bulk of a bone. Both the polarized L-XRF and {sup 109}Cd K-XRF achieve similar precision. Renal mercury has recently been determined using a polarized x-ray source, Both renal and hepatic cadmium can be measured using polarized x-rays in conjunction with a Si(Li) detector. Platinum and gold have been measured both by radioisotopic source excitation and by using polarized x-rays, but the latter is to be preferred. Applications of Pb K-XRF have shown that measured bone lead relates strongly to cumulative lead exposure. Secondly, biological half lives of lead in different bone types have been estimated from limited longitudinal data sets and from some cross sectional surveys.more » Thirdly, the effect of bone lead as an endogenous source of lead has been demonstrated and it has been shown that a majority of circulating blood lead can be mobilized from bone, rather than deriving from new exposure, in some retired lead workers. 35 refs., 5 tabs.« less