URINARY CHROMIUM AS A BIOLOGICAL MARKER OF ENVIRONMENTAL EXPOSURE - WHAT ARE THE LIMITATIONS

Public concern has mounted recently about environmental exposures to c hromium in soil, tap water, and ambient air. In response, agencies cha rged with protecting public health have attempted to study exposure by monitoring urinary chromium levels among potentially exposed populati ons. While urinary biomonitoring of occupationally exposed workers has been successfully used to assess high-level inhalation exposures in t he workplace, evaluating low-level environmental exposures has been pr oblematic. Due to these problems, before an extensive biological monit oring study is conducted of those exposed to low levels of environment al chromium, several issues must be resolved. First, exposures to chro mium must occur at the same time as sampling, because the biological h alf-life of chromium in urine is very short (less than 2 days). Second , reduced bioavailability and bioaccessibility via the oral and dermal routes of exposure limit the capacity of urinary monitoring to measur e environmental exposures (e.g., systemic dose is too small to be meas ured). Third, the dose of chromium must be sufficient such that it may be reliably measured above background levels in urine (range of 0.2 t o 2 mu g/liter) and above the analytical limit of detection (0.2 mu g/ liter). Fourth, the inter-and intrapersonal variability in background levels of urinary chromium is known to be significant and influenced b y food and beverage intake, smoking, and exercise. Thus, the role of e ach factor must be carefully understood. Finally, it is imperative to have developed a complete understanding of the clinical significance o f elevated urinary chromium levels before a study is performed, becaus e higher than background levels, in and of themselves, are not indicat ive of a significant health concern. The route of exposure, valence of chromium to which people were exposed, exposure time, and duration mu st all be understood before the biological data can be implemented. We have conducted a total of nine human exposure studies over the past 3 years in an attempt to understand the kinetics of chromium and the im pact on urinary, red blood cell (RBC), and plasma biomonitoring progra ms. The results of these studies are described here and our recommenda tions are offered for how to design and implement a urinary chromium b iomonitoring study. In our view, given some evidence that the dose of hexavalent chromium [Cr(VI)] is sufficient to be measurable above back ground concentrations of total chromium [Cr(III) and Cr(VI)], duplicat ed measurements of chromium in plasma and RBCs are, in most cases, a m ore definitive gauge of environmental exposure than urinary biomonitor ing. (C) 1997 Academic Press.