Measurement, environmental lead

ALAD, an enzyme occurring early in the heme pathway, is also considered a sensitive indicator of lead effect (Hemberg et al. 1970 Morris et al. 1988 Somashekaraiah et al. 1990 Tola et al. 1973). Because there is no well-defined blood lead threshold at which inhibition of ALAD does not occur, it allows measurement of the effect on the general population at environmental lead levels and does not require high exposure levels as with occupational workers (Hemberg et al. 1970). However, ALAD activity may also be decreased with other diseases or conditions such as porphyria, liver cirrhosis, and alcoholism (Somashekaraiah et al. 1990). 

Flegal AR, Smith DR. 1995. Measurements of environmental lead contamination and human exposure. Rev Environ Contam Toxicol 143 1-45. 

Pocock SJ, Smith M, Baghurst P Environmental lead and children s intelligence a systematic review of the epidemiological evidence. BMJ 309 1189-1197, 1994 Rice DC The health effects of environmental lead exposure closing Pandora s box, in Behavioral Measures of Neurotoxicity. Edited by Russell RW, Llattau PE, Pope AM. Washington, DC, National Academy Press, 1990, pp 243-267... 

Delves, H.T., Clayton. B.E., Carmichael, A.. Bubear, M. and Smith. M. (1982). An appraisal of the analytical significance of tooth lead measurements as possible indices of environmental exposure of children to lead. Ann. Clin. Biochem., 12.329-337. 

NHANES II blood lead measurements found a substantial decline in blood lead levels, 10 times more than predicated by environmental modeling... 

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. 

The approved reference method for enforcement purposes (CFR, 1982, 40 58) uses hi-vol samplers and measures lead by atomic absorption spectrometry (AAS). This laboratory method, which has been available in various analytical configurations for several decades, has been shown to be particularly reliable and sensitive for measuring lead quantitatively in a large range of environmental media. Flameless AAS is a more sensitive variation of this technique than conventional flame methods and has been the choice for many years. As with any lead measurement method, sample handling must minimize both contamination with lead and loss of lead from the sample. Comparatively, the contamination problem is still the more problematic and this is certainly the case for analyses in U.S. urban areas and in other industrialized nations (NAS/NRC, 1993 Patterson, 1983 Settle and Patterson, 1980). For air sample analyses, the codified reference method using AAS is quite adequate for a wide range of air lead concentrations. 

U.S. EPA (2001) holds ICP-AES or ICP-MS to be the soil lead measurement methods of choice. Detection hmits are on the order of 40 parts per bU-hon (ppb) which are quite adequate for an environmental medium where even background, i.e., uncontaminated soil lead, concentrations are on the order of 10—20 ppm. 

Concentrations of lead in the various environmental media described in this section are presented for extended periods. The available data that meet minimal statistical and measurement criteria generally only extend from the late 1960s/early 1970s to the present. The purposes of a wide temporal look at environmental lead concentrations are several. First, the nature of lead as an accumulating contaminant in the bodies of human populations requires an appreciation of the amounts of environmental lead that existed in past decades. As noted earlier, lead levels in media have been changing, mainly downward, so that current human body lead burdens are only partially quantifiable from current lead intakes into body compartments. Secondly, the use of predictive, biokinetic models of human lead exposures for simulating Ufe-time lead exposures requires knowledge of lead intakes from the earliest periods of life. 

National Academy of Sciences National Research Council, 1993. Measuring Lead Exposure in Infants, Children, and Other Sensitive Populations. National Academy Press, Washington, DC. Nriagu, J.O., 1983. Lead and Lead Poisoning in Antiquity, lohn Wiley Sons, New York. Nriagu, J.O., 1985. Historical perspective on the contamination of food and beverages with lead. In Mahaffey, K.R. (Ed.), Dietary and Environmental Lead Human Health Effects. Elsevier, New York, pp. 1—41. 

Scientists measure the amounts of the materials that make up everything in our universe. An engineer determines the amount of metal in an alloy or the volume of seawater flowing through a desalination plant. A physician orders laboratory tests to measure substances in the blood such as glucose or cholesterol. An environmental chemist measures the levels of pollutants such as lead and carbon monoxide in our soil and atmosphere. 

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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