Introduction

Biomonitoring is an emerging approach to quantify exposure (i.e., via blood and urine samples) to potential environmental toxicants rather than inferring exposure from environmental media concentrations such as in air or drinking water.

As a part of the Centers for Disease Control and Prevention (CDC), the National Center for Health Statistics (NCHS) conducts the National Health and Nutrition Examination Surveys (NHANES). NHANES is the only biomonitoring national survey that collects extensive health information from personal interviews, medical examinations, and laboratory analyses from biological specimens such as urine and blood. Data from NHANES surveys have provided unique opportunities to study human nutrition, infection, and environmental and chronic health conditions in the U.S. population. Further, the NHANES studies provide informative baseline biomonitoring data with which to make spatial and temporal comparisons.

An excellent example of the usefulness of biomonitoring studies regards the lead exposure trend within the U.S. population. Specifically, the decline of leaded gasoline corresponds with the decline in human blood lead levels. Interestingly, previous models had indicated that there would be a less notable decline in blood lead levels as a result of decreased lead in gasoline; however, these models failed to consider, for example, the contribution of lead in dust as a major contributor to blood lead levels. As a result of direct biomonitoring measurements and mandated actions by legislation, blood lead levels have continued to decline in the U.S. population to an average of less than 2 ug/dL. Thus, the use of biomonitoring data to verify exposure is of particular importance to humans.

The goals of our biomonitoring program are to assess human exposures to environmental toxicants, including estimates of background exposure to naturally occurring chemicals that have the potential to cause harm to New Mexico residents.

Preliminary biomonitoring results for New Mexico

To date, we have conducted exposure assessments to quantify concentrations of heavy metals in drinking water, urine, and hair samples from approximately 1,000 residents of New Mexico. Subsequently, we are in the process of comparing the New Mexico results with those national results obtained in the NHANES study.

A case in point: We quantified uranium in participants' urines and household drinking water and compared these data with national levels and drinking water standards to determine potential geographic regions of clustering. Some geographical regions of the United States, particularly western states such as New Mexico, exhibit higher-than-average uranium levels due to natural geological formations coupled with mining activities, and these higher levels may result in increased risk of human exposure and subsequent adverse health effects. Elevated uranium levels are associated with local uranium geological deposits and regional groundwater.

Relatively higher rates of uranium intake have been reported for some populations. For example, the potential for uranium intake is greater for individuals who consume foods grown in areas with elevated concentrations of uranium in the soil, and for individuals with elevated concentrations of uranium in their drinking water. Most of the drinkable uranium originates from dissolved uranium present in the rocks and soil that groundwater encounters.

The health effects associated with oral or dermal exposure to natural uranium appear to be solely chemical in nature and not radiological. In animals, kidney damage is the principal toxic effect of uranium, especially the soluble uranium compounds. Thus, relatively high oral doses of uranium have caused renal damage in humans. Lastly, liver and developmental effects have been noted in some animal studies.

For New Mexico, approximately 10% of the biomonitoring participants' household water contained uranium concentrations that exceeded the U.S. Environmental Protection Agency (EPA) drinking water standard of 30 ug/L. Figure 2 shows that participant urine uranium levels have a geometric mean of 0.026 ug/L (95th percentile = 0.31 ug/L) - almost 3 times greater than the 2001-2002 National Health and Nutrition Examination Survey (NHANES) age group equivalent mean of 0.009 ug/L (95th percentile = 0.046 ug/L). For Rio Arriba County in particular, the urine uranium geometric mean is 0.081 ug/L – approximately 9 times greater than the NHANES mean.

Among the samples collected during the biomonitoring surveillance, we identified statistically significant clusters of co-located urine and water uranium levels. The most likely cluster comprised 22% of the total biomonitoring participants residing within a 14.7-km radius encompassing two adjacent counties (Santa Fe and Rio Arriba), and the spatially-aggregated water and urine uranium geometric means are 8.2 ug/L and 0.089 ug/L, respectively. Additionally, data collected from 78% (97/124) of Rio Arriba County participants were in this cluster, as were 61% (62/101) of Santa Fe county participants. New Mexico biomonitoring participant urine uranium levels have a geometric mean almost 3 times greater than the 2001-2002 NHANES age group equivalent mean. For Rio Arriba County in particular, the urine uranium geometric mean is approximately 9 times greater than the NHANES mean.

Elevated blood and urine uranium levels due to environmental exposure are preventable. Given that most environmental exposure to uranium is via the ingestion of drinking water, it is imperative that drinking water in uranium-rich geographic regions be treated with reverse osmosis. The results of this investigation are noteworthy in that these are the first biomonitoring uranium data to be quantified for the state of New Mexico, and the resulting elevated levels will lead to mitigation of the exposure in several high-risk communities. And, these results will direct further study as part of our CDC Environmental Public Health Tracking Program to link these exposure data with health outcome data.

National Health and Nutrition Examination Survey – NHANES(external Web site)