Urinary biomarkers body burden

Urinary lead levels have also been used to measure current exposure (Robinson 1974) but they are of questionable value as biomarkers of exposure because of the relatively low and fluctuating lead levels that are excreted in the urine (ACGIH 1986 Ibels and Pollock 1986 Jensen 1984). In contrast, the determination of urinary lead following a single injection of the chelating agent, calcium disodium EDTA, which mobilizes extracellular lead and produces increased urinary excretion of lead, is presumed to be indicative of an elevated body burden of lead (Cory-Slechta et al. 1987 Ibels and Pollock 1986 Janin et al. 1985). Children whose PbB levels are 45 pg/dL should not receive a provocative chelation... 

Case Example Pharmacokinetic Calculations to Interpret Phthalate Urinary Biomarker Data. The previous descriptions focused on blood or adipose biomarker concentrations that were converted to body burden to yield estimates of daily dose based on chemical half-life. A modified form of that is conversion of urinary biomarker data to daily exposure dose via simple model calculations as described for phthalates. 

The preferred biomarkers of exposure are generally the substance itself or substance-specific metabolites in readily obtainable body fluid(s) or excreta. However, several factors can confound the use and interpretation of biomarkers of exposure. The body burden of a substance may be the result of exposures from more than one source. The substance being measured may be a metabolite of another xenobiotic substance (e.g., high urinary levels of phenol can result from exposure to several different aromatic compounds). Depending on the properties of the substance (e.g., biologic half-life) and environmental conditions (e.g., duration and route of exposure), the substance and all of its metabolites may have left the body by the time samples can be taken. It may be difficult to identify individuals exposed to hazardous substances that are commonly found in body tissues and fluids (e.g., essential mineral nutrients such as copper, zinc, and selenium). Biomarkers of exposure to CDDs are discussed in Section 2.7.1. 

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