PHYTOREMEDIATION OF DEPLETED URANIUM IN AN ARID ENVIRONMENT

Since the 1970s, depleted uranium (DU) has been used in military armor-piercing munitions and tank armor by a number of countries worldwide, in particular the United States and the Soviet Union. DU is not considered a radiation hazard because it emits relatively low levels of gamma radiation, although it still emits high levels of alpha radiation. Ingestion and/or inhalation of DU can cause organ damage because of its heavy metal toxicity.

Numerous studies in more temperate environments have been undertaken to determine the properties of DU in soils and groundwater and to develop technologies to remove or stabilize the metal in the environment. Far fewer studies have been conducted in more complicated arid to semi-arid environments.

A study targeting DU-bearing soils (averaging 40 mg/kg) at an inactive munitions testing site in New Mexico was begun in 2001. The goals of the study included: 1) to characterize the site, 2) to determine DU mobility in arid environments, 3) to compare the DU bio-accumulation potential of selected non-native and native arid plant species, 4) to determine if the plant’s biomass and ability to uptake DU make it a viable economic remediation technique, and 5) to test a variety of soil and plant amendments and to determine their impact on the plant’s ability to accumulate DU.

Uranium distribution patterns at the site were determined by analyzing soils by ICP-MS. A test garden area was then selected based on its DU concentration and soil cover. Native and non-native plant species were grown in the test garden and in containers filled with soil from the area. The non-native Indian mustard (Brassica juncea) plants, especially when treated with citric acid, provided promising results, but required far more water than is normal for an arid environment. Plants better adapted to the hot, dry conditions of the desert southwest that have shown promise include: Russian thistle (Salsola tragus) and grain crops (quinoa (Chenopodium quinoa) and purple amaranth (Amaranthus blitum)). Citric acid and other treatments also enhance the plants’ ability to accumulate uranium.

In conclusion, soil data indicates that DU is mobile even in arid environments, and while the plant data is promising, no plant species appears to offer a short-term alternative to traditional remediation technologies in arid environments.