Nitrates in fertilizers can transfer natural uranium to groundwater. Reported by the University of Nebraska at Lincoln.
Scientists have long realized that water-soluble inorganic carbon compounds can scavenge uranium found in the earth’s crust. Also, this mixture can penetrate groundwater, increasing the level of uranium in it. Now researchers have confirmed that nitrates may play a similar role.
To find out, the study’s authors extracted two cylindrical rock cores, each about 5 centimeters wide and 20 feet deep, from an aquifer near Alda, Nebraska. There is a lot of uranium in the soil in this area, and groundwater flows east into the nearby Platte River. The authors wanted to recreate the natural flow of water in these sediments and then determine whether adding nitrate to the water would increase the amount of uranium carried along with it.
As a result, the scientists pumped an analog of groundwater through the cores at the rate they flow in nature. In some cases, in addition to nitrates, an inhibitor designed to stop the biochemical activity of microorganisms living in the sediment is added to the water. Water containing nitrates but no microbial inhibitors was able to remove about 85% of the uranium; it was 55% when the water was nitrate-free, and 60% when it contained nitrates as well as inhibitors.
From this it follows that nitrates are pathways to leach uranium into groundwater, and the conversion of uranium to a soluble compound is related to the activity of microbes.