Tumbleweeds may seem like the ultimate loner plant, but in the future, they may cooperate with environmentalists to clean up toxic waste.


A military job for tumbleweeds. I'm Bob Hirshon and this is Science Update.

Military test sites are often contaminated with depleted uranium, a toxic heavy metal used in armor-piercing bullets. To clean it up, the Army should consider enlisting tumbleweeds. That's according to Dana Ulmer-Scholle, a senior research scientist at the New Mexico Institute of Mining and Technology.

She and her colleagues tested a wide variety of desert plants to see how well they soaked up the uranium.


And so we actually did a survey of probably close to 100, 150 plants, looking for what their background uranium values were at the end of the growing season. And tumbleweeds, and another tumbleweed-like plant, kosha, were our best accumulators.

Even better, she says the tumbleweeds do their work before they flower or seed. That means the cleanup crew could uproot the plants before they start blowing all over town. I'm Bob Hirshon for AAAS, the Science Society.

Making Sense of the Research

This is just one of many examples of a scientific technique called phytoremediation. Simply put, phytoremediation is the use of plants to clean up pollution. Plants naturally absorb chemicals from the environment through their roots. Many chemicals that are toxic to people and animals are harmless or even beneficial to certain plants.

The key is figuring out which plant to use in which situation. It's been well known for some time that certain plants can absorb uranium. However, this study identifies a plant that not only absorbs a lot of uranium, but also grows relatively quickly with very little water–perfect for the desert environments in which many military testing grounds are located. What's more, the tumbleweeds are easy to harvest after they're finished soaking up the uranium. That's important because once tumbleweeds detach and start blowing in the wind, they become nuisances: they're able to spread their seeds for miles, and sometimes they even cause car accidents.

Nobody knows exactly what the tumbleweeds do with the uranium once they soak it up. Ulmer-Scholle suspects they may use the metallic element to make pigments, but this hypothesis has not been tested. The health risks of depleted uranium are also somewhat unclear. Inhaling or swallowing heavy metals like uranium can damage the kidneys and possibly the lungs, but exactly how much you can take in without causing damage has been heavily debated. Depleted uranium is also a suspect in many unexplained military illnesses like "Gulf War Syndrome." Again, this hasn't been proven.

Regardless, it's certainly better to remove potentially hazardous pollutants than to leave them in the environment. While tumbleweeds might help, they do have some limitations. They require people to plant them, wait for them to grow, and harvest them. Because they take time to grow, they're best suited for sites that are no longer being contaminated. Finally, they must be planted on sites that are known to be contaminated, but Ulmer-Scholle's research also found that depleted uranium may spread to neighboring areas.

Now try and answer these questions:

  1. What is phytoremediation?
  2. What are the advantages of tumbleweeds for this particular sort of cleanup?
  3. What kinds of sites that might be contaminated with depleted uranium are best suited for tumbleweeds? What kinds of sites would not be well suited?
  4. Why is phytoremediation an attractive solution to some environmental problems?

For Educators

Depleted Uranium: Questions and Answers about Its Use in War, by the International Institute of Concern for Public Health, quotes researchers from the Boston University School of Public Health on the risks of depleted uranium.

Phytoremediation is another site, created by John Cross and hosted by the Missouri Botanical Garden, with lots of links and information.

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