Uranium contamination in the environment caused by past mine activities is a severe problem for the people who live near the abandoned mines on the Navajo Nation. Studies have shown that some wells on the Navajo Nation have elevated levels of uranium in the water. Both water and soil are suspected pathways of uranium exposure to the Navajo. A third possible uranium pathway is plants. The objectives of our studies are to determine if wild plants contain elevated levels of uranium, and to test whether a native forage grass acquires uranium from water and/or from soil. We analyzed the uranium content of three species of plants, Sporobolus airoides, Gutierrezia sarothrae, and Atriplex canescens, which were collected near Cameron, Arizona, in the southwestern part of the Navajo Nation. We also conducted a two factor greenhouse study to determine the amount of uranium taken up by S. airoides when it is exposed to different sources of uranium in soil and water. Plants were grown in soil containing high (3.42 ppm) or low (0.24 ppm) levels of uranium and watered with three sources of water: distilled water, well water contaminated with uranium, and distilled water with a known amount of uranium added to it. Plants were grown for four months and then analyzed for uranium using the inductively coupled plasma-mass spectrometer (ICP-MS).
Results/Conclusions
All three species of plants collected at Cameron had elevated levels of uranium ranging between 5.64 ppm to 7.32 ppm. Our greenhouse study showed that Sporobolus airoides took up more uranium from the high contaminated soil but not as much from the low contaminated soil. The different water sources used in the greenhouse study did not have a significant effect on the uptake of uranium in S. airoides. Some plants grown in the high uranium soil contained up to 11 ppm of uranium. The plants grown in low uranium soil contained an average of 5 ppm of uranium. These results mean that plants growing in soil with high uranium content may affect the animals that eat them. In addition, these results are important for the people living near the abandoned uranium mines because some of these people consume these animals, which may provide harmful health effects for the people.
