Human exposure, lead measurement techniques

For measuring lead in environmental media providing potential human lead exposures, this chapter includes older published data for lead concentrations in media, data which are old enough to encompass the full lifetimes of living populations. This is because of long-term Pb storage in bone. One concern with any appraisal of older lead measurement data in media is that of analytical and statistical data reliability versus that of methods employed with more recent accepted techniques. Sensitivity is of particular concern. A potent toxicant such as environmental lead requires methods for quantification of concentrations of lead at ultra-trace levels in order to permit estimates of the full range of Pb exposures. 

Environmental media of interest in this section on measurement are the same as those producing potential human lead exposures ambient air, lead paints, diet, drinking water, soils and dusts, and some of the more problematic idiosyncratic sources. Sampling and laboratory measurement techniques now widely used are emphasized with comparative statements for older methods provided mainly to offer perspective. Biomarker sampling and measurement methodologies, i.e., procedures for lead in biological media directly relevant to human lead exposures, are presented in a later chapter. 

Other neurochemical studies have not been carried out in lead-exposed humans. It is difficult to measure neurochemical functions in vivo without recourse to such techniques as cerebrospinal fluid collection. However, the reported effects of lead exposure in rodents on plasma concentrations of prolactin (Govoni et al., 1978) and other pituitary hormones (Petrusz et al., 1979), and tetrahydrobiopterin (Leeming and Blair, 1980 McIntosh et al., 1982) would suggest that similar studies in humans might be considered. 

Consequently, this review is designed to briefly summarize many of the available techniques for accurate measurements of environmental and human lead contamination. This includes the importance of ultraclean techniques for lead analysis as well as brief descriptions of some current and emerging analytical techniques for measuring lead exposures in humans. The descriptions are preceded by abbreviated discussions of the chemical properties of lead, natural and anthropogenic variations in its stable isotopic composition, and historical records of lead contamination in the environment. The report concludes with a summary of some indirect methods of measuring lead exposure and toxicity in humans. Much of the material in this report is based on reviews written for several recent reports Measuring Lead Exposure in Infants, Children, and Other Sensitive Populations (NRC 1993), Lead in the Biosphere Recent Trends (Smith and Flegal 1995), and In Vivo Measurement and Speciation of Nephrotoxic Metals (Smith and McNeill 1995). 

Trace-metal-clean techniques are also necessary in analysis of clinical samples with relatively low lead concentrations. This is illustrated by the relative contribution of contaminant lead in measurements of elevated (50 fig/dL) and low (1 /xg/dL) PbB (Fig. 8). Moreover, the importance of these techniques will increase in clinical settings with projected declines in environmental lead exposures to humans in the U.S. and elsewhere (Brody et al. 1994 Flegal and Smith 1992b Smith and Flegal 1995). 

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