Salsola kali (tumbleweed): A possible biomonitoring device for the detection of airborne heavy metals

Tenoch Benitez, University of Texas at El Paso


Vehicular congestion generates particulate matter and contaminants such as lead, cadmium, copper, chromium, nickel, and zinc which have been detected in the U.S.-Mexico border region. To overcome the inconvenience of expensive sampling techniques, scientists started to assess air quality by using bioindicator plants, a technique called biomonitoring. Biomonitoring is an inexpensive and environmentally friendly approach to determine inorganic contaminants at trace levels. The purpose of this project was to determine the effectiveness of tumbleweed (Salsola kali) plants, sprayed with chelating agents, as a passive monitoring device to determine the possible presence of heavy metals in the ambient air around international ports of entry in the El Paso-Ciudad Juarez border region. Plants were germinated and grown for three months in black plastic bags packed with 1 kg of soil. After three months, citric acid and EDTA were applied to plant canopies, separately, at 0.1, 0.5, and 1.0 mM concentrations. The plants were then set at the international ports of entry of Santa Teresa and Zaragoza, and a third site close to UTEP. Four replicates and a control were used for each concentration and each chelating agent. The tumbleweed plants were kept for 4 weeks at each experimental site. In order to evaluate the feasibility of a biomonitoring program using natural vegetation, wild tumbleweed plants were collected in the vicinity of the experimental sites during the months of February, March, May, and April of 2008 and analyzed for metal content in the foliage. In all cases the plants were harvested and the shoots were processed for metal determination using ICP-MS or ICP-OES. Samples of surface soil were also taken from the pots and the wild area and analyzed for metal content. Results showed that tumbleweed plants were naturally capable of capturing contaminants from the surrounding atmosphere. Four elements were consistently found in the plants: Cu, Cd, Cr, and Ni. The chelating agents seemed effective in enhancing the plant’s natural abilities to capture Cd. The capture of Cu was enhanced only when high amounts of this metal were present. Results also suggested that the metal capture was affected by degree of affinity of the chelating agent. Due to this, the capture of Cr and Ni was reduced whenever high concentrations of Cu and Cd were available. The wild plants showed to have in the foliage all the elements present in soil plus selenium, which was consistently found in plants but not in soil. The amount of Se in plants was related to the atmospheric deposition cycle of the element. This study showed that tumbleweed was able to capture elements from the ambient air and that has capabilities for being used as a passive biomonitoring device for metal contamination.

Subject Area

Chemistry|Analytical chemistry|Environmental science

Recommended Citation

Benitez, Tenoch, "Salsola kali (tumbleweed): A possible biomonitoring device for the detection of airborne heavy metals" (2009). ETD Collection for University of Texas, El Paso. AAI1473853.