Toxic Substances Hydrology Program
Using Plants To Detect Tritium Contamination
USGS scientists have developed a new cost-effective method for identifying the occurrence and distribution of tritium contamination in the subsurface that uses plants as "tritium detectors." Desert plants efficiently scavenge for water in the soil root-zone, and if the water contains tritium the tritium is absorbed along with the water. As a result, the concentration of tritium in the water in plants is correlated to the concentration of tritium in the soil water on which the plants rely for survival. Thus, the plants can be used to rapidly assess and map the size and shape of tritium plumes in the shallow unsaturated zone at contaminated sites.
The method involves collecting plant foliage samples followed by solar distillation of the leaves in plastic bags on site to collect plant water. The collected water is taken to the laboratory and processed to remove constituents that can interfere with subsequent tritium analysis. The simplified method is of sufficient accuracy to facilitate optimized placement of more sophisticated (and costly) monitoring equipment. The new method is also a time saver! Collection and preparation of samples can be done in one-fourth the time required by the standard chemical-extraction method or by soil-gas sampling.
The method is based on research that USGS scientists conducted at the Amargosa Desert Research Site (ADRS) on the importance of plants in the water balance and the movement of water in the deep (110-meter-thick at the ADRS) unsaturated zones of deserts in the southwestern United States. This method is one more tool that will help scientists provide resource managers with the information needed to make informed decisions about waste disposal in arid environments. Deserts are often candidates for waste disposal because of their unique characteristics and lack of water.