PUBLIC HEALTH CONCERNS OF URANIUM IN GROUNDWATER IN NEW MEXICO

Natural uranium has been detected at concentrations exceeding the EPA drinking-water standard of 0.03 mg/L in many public and private water supply wells in the Española Basin, the Grants-Gallup mineral belt, Las Cruces, Tucumcari, and in other communities in New Mexico. Excessive detections are often associated with Proterozoic granitic rocks, the Jurassic Morrison Formation, Cenozoic volcanic ash, or with sediments derived from these rocks. Uranyl carbonate complexes [UO₂(CO₃)⁰, UO₂(CO₃)₂^2-, and UO₂(CO₃)₃^4-] are the most common uranium species in natural water.

Most uranium ingested in drinking water is excreted in urine within several days, but some uranium is stored in the body, primarily in the bones, liver and kidneys. The primary health concern of ingested uranium is chemical kidney toxicity. The EPA drinking-water standard is intended to address both nephrotoxicity and radiation hazards of alpha particles emitted by uranium isotopes. Urine testing can determine if a person has recently been exposed to high levels of uranium via ingestion or inhalation. Detection of greater than 0.08 µg/L of uranium in urine is a “notifiable condition” that must be reported to the New Mexico Department of Health.

Concentrations of uranium in drinking water can be decreased by blending, and by anion exchange or membrane filtration treatment technology. Public water utilities often use blending due to the high cost of water treatment. Many private domestic well owners have installed household treatment systems. Since the health risk of uranium in well water is from ingestion, point-of-use (kitchen sink) treatment systems are suitable in household situations. Membrane filtration with effective pore size of 0.001 µm decreases uranium concentrations while minimizing water consumed by the treatment process, relative to reverse osmosis with effective pore size of 0.0001 µm. Management of uranium-bearing drinking-water treatment waste, which is often discharged to an onsite wastewater system, is an emerging issue.