SOIL POLLUTION AND UNDERGRADUATE RESEARCH IN EL PASO, TEXAS

Elevated levels of lead, copper, and arsenic in the soils of El Paso, Texas, (Barnes, 1993, U.S. EPA, 2002) have raised environmental and health concerns for area residents. The geography of El Paso and number of potential heavy metal sources presents a rich opportunity to teach undergraduate students about science and research as well as to contribute to the understanding of soil pollution in El Paso.

Our study, funded by the National Institutes of Health, compares four methods of soil analysis; for cost, effectiveness, and usefulness of results. Over 100 samples were collected from the El Paso area and tested using magnetic susceptibility, Inductively coupled plasma – optical emission spectroscopy (ICP-OES), Accumetrics Cu analysis, and Botsford's toxicity assay. Magnetic susceptibility results proved useful as a preliminary, fast, and relatively inexpensive screen to indicate which soils should be tested further. ICP-OES provided total concentrations and types of heavy metals in the soil, but was the most expensive method and could not determine bioavailability directly. The Accumetrics test was fast and relatively simple but could only test a narrow range of concentrations for one metal. Botsford's toxicity assay is a colorimetric test that uses the bacterium Rhizobium meliloti to determine if water soluble extracts of the soil are toxic. These toxicity results showed Rhizobia are very sensitive to heavy metals, so that most El Paso soils tested toxic to some degree. Modifying Botsford's test to measure the toxicity of serial dilutions is a useful measure of relative toxicity. All of these methods can be done by undergraduate students and proved a very valuable way to allow students to participate in scientific research.

Barnes (1993) An Evaluation of Metals concentrations in surficial soils, El Paso County, Texas, Thesis, University of Texas at El Paso. Botsford (2000) A Simple, Inexpensive, and rapid method to determine toxicity using a bacterial indicator organism, Proceedings of the 2000 Conference on Hazardous Waste Research, p. 22-35. U.S. EPA (2002) El Paso County Metals Survey.