Academic journal article Environmental Health Perspectives

A Critical Review of Biomarkers Used for Monitoring Human Exposure to Lead: Advantages, Limitations, and Future Needs

Academic journal article Environmental Health Perspectives

A Critical Review of Biomarkers Used for Monitoring Human Exposure to Lead: Advantages, Limitations, and Future Needs

Article excerpt

Lead concentration in whole blood (BPb) is the primary biomarker used to monitor exposure to this metallic element. The U.S. Centers for Disease Control and Prevention and the World Health Organization define a BPb of 10 [micro]g/dL (0.48 [micro]mol/L) as the threshold of concern in young children. However, recent studies have reported the possibility of adverse health effects, including intellectual impairment in young children, at BPb levels < 10 [micro]g/dL, suggesting that there is no safe level of exposure. It appears impossible to differentiate between low-level chronic Pb exposure and a high-level short Pb exposure based on a single BPb measurement; therefore, serial BPb measurements offer a better estimation of possible health outcomes. The difficulty in assessing the exact nature of Pb exposure is dependent not so much on problems with current analytical methodologies, but rather on the complex toxicokinetics of Pb within various body compartments (i.e., cycling of Pb between bone, blood, and soft tissues). If we are to differentiate more effectively between Pb stored in the body for years and Pb from recent exposure, information on other biomarkers of exposure may be needed. None of the current biomarkers of internal Pb dose have yet been accepted by the scientific community as a reliable substitute for a BPb measurement. This review focuses on the limitations of biomarkers of Pb exposure and the need to improve the accuracy of their measurement. We present here only the traditional analytical protocols in current use, and we attempt to assess the influence of confounding variables on BPb levels. Finally, we discuss the interpretation of BPb data with respect to both external and endogenous Pb exposure, past or recent exposure, as well as the significance of Pb determinations in human specimens including hair, nails, saliva, bone, blood (plasma, whole blood), urine, feces, and exfoliated teeth. Key words: biomarkers, biomonitoring, blood, bone, feces, hair, lead, plasma, saliva, teeth, toxicokinetics, urine. Environ Health Perspect 113:1669-1674 (2005). doi:10.1289/ehp.7917 available via http://dx.doi.org/[Online 11 August 2005]

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Over the last two decades, atmospheric concentrations of lead have decreased significantly around the globe as more and more nations have chosen to remove tetraethylead from gasoline (Thomas et al. 1999). However, humans may also be exposed to Pb through contaminated food, water, and house dust and through industrial activities such as metal recycling and the battery industry. In the United States, for example, although the use of Pb in house paint peaked in 1940 and was banned in 1978, 40% of the nation's housing stock is estimated to still contain Pb-based paint (Wakefield 2002).

After Pb enters the body, it can travel along several pathways depending on its source and, by extension, its bioavailability. The fraction of Pb that is absorbed depends mainly on the physical and chemical form, particularly particle size and the solubility of the specific compound. Other important factors are specific to the exposed subject, such as age, sex, nutritional status and, possibly, genetic background [Agency for Toxic Substances and Disease Registry (ATSDR) 1999; National Research Council 1993]. One of the earliest toxicokinetics studies reported that Pb, once absorbed into the blood compartment, has a mean biological half-life of about 40 days in adult males (Rabinowitz et al. 1976). The half-life in children and in pregnant women was reported to be longer, because of bone remodeling (Gulson et al. 1996; Manton et al. 2000). However, another study was unable to confirm this finding (Succop et al. 1998).

Like many other "bone-seeking" elements, Pb from blood is incorporated into calcified tissues such as bone and teeth, where it can remain for years (Rabinowitz 1991; O'Flaherty 1995). According to Rabinowitz (1991), the half-life of Pb in bone (bone-Pb) ranges from 10 to 30 years. …

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