Do uranium levels in water pose a threat?

In late December, Carson City Public Works sent out letters to homeowners on the west side of Carson City stating that monitoring tests showed a slightly elevated level for uranium at one sample site. The standard is 30 parts per billion and the test result indicated 31.08 parts per billion. This is not an immediate risk and resulted from a lack of water normally received from Marlette Lake due to reconstruction of that system. Once the Marlette System is up and running this fall, levels are expected to drop below required standards again.

The notice generated a question from my friend Cathy about whether elevated levels of uranium would hurt people and plants. Cooperative Extension's water quality specialist Dr. Mark Walker pointed out that setting standards "is convoluted and involves a lot of assumptions related to level of exposure to a chemical and the kinds of data that EPA has to work with." He pointed out that there is a safety factor built in, in this case a factor of 100. The standard is conservative.

Uranium is found almost everywhere in the earth's crust, so we can't completely avoid it. Our bodies actually contain uranium that is generally derived from foods, such as vegetables and cereals.

Studies on edible plants such as lettuce, tomatoes, sunflowers, peppers and radishes show that they can absorb uranium and concentrate it in their roots, leaves and other parts when there is uranium in the soil and/or water. People can ingest it when they eat the affected plant. Different plants have differing uptake capacity. The age of the plant affects the uptake capacity. Uranium is not an essential nutrient to plants such as nitrogen or phosphorus. Its nature as a heavy metal is more of a problem to plants than its radioactivity. According to scientists studying the effect of uranium on plants, growth of the plant can be affected with increase in concentration of uranium in the soil underneath.

Since the city is minimizing the use of wells that have uranium, we are not likely to have uranium contamination to our drinking water or to the water we use to water plants. You can help decrease the demand on the wells this summer by conserving and not wasting water, particularly during July, August and September.

For information, contact me, (775) 887-2252 or skellyj@unce.unr.edu, your local University of Nevada Cooperative Extension office or at www.unce.unr.edu. "Ask a Master Gardener" at mastergardeners@unce.unr.edu

n JoAnne Skelly is the Carson City/Storey County Extension educator for University of Nevada Cooperative Extension.