Apparently during a regular check of the site some radioactive contamination was found in the ground near one of the storage tanks. The area was promptly cleaned up, the soil carted away and replaced, but the people assigned to figure out how the ground became contaminated in the first place were stumped. They found no leaks, no spills, nothing that could have caused the radioactive material to escape. They checked over the spot for several months to see if the contamination recurred, which it did not, then finally shrugged and called it a mystery.
But a year later the contamination was back.
The second time was much like the first. The clean-up went smoothly, the investigation did not. It was not until the third time the same contamination recurred in the same place that the investigators found the culprit – an oak tree. The tree had sunk its roots into the tank, and was pulling up contaminated material. While one would expect the whole tree to become radioactive, that wasn’t the case. Instead the oak preferentially shunted the contaminants to its leaves. Every fall a new crop of radioactive leaves would hit the ground to mystify the workers at Oak Ridge, and every winter while they were investigating, there would be no sign of anything amiss with the tree.
It’s an amusing story, but the ability of that tree has become a major weapon in the efforts to clean up contaminated soil. You see, trees aren’t the only plants that can pull contaminants from the ground. There are a slew of others that can do it too, and they are becoming more and more valuable in places where the ground has become polluted or contaminated.
The process is called phytoextraction, and it’s one of a number of ways ecologists are beginning to use plants in bioremediation – the treatment of environmental problems. There are plants that can pull lead, uranium, arsenic, and any number of other contaminants out of the soil. They can then be harvested, a new crop planted, and the process repeated until the soil is sufficiently recovered.
All in all, the field of phytoextraction seems to be one of the most promising in the efforts to clean up the hundreds of thousands of sites worldwide (30,000 in the US alone, according to the EPA), that require hazardous waste treatment. Even if only modestly successful, the use of plants as contaminant removers could reduce cleanup costs considerably. Even more promising, phytoextraction is only one aspect of the whole field of phytoremediation, in which plants are being used not only to remove toxins, but sometimes to break them down (phytotransformation), enhance microbial activity (phytostimulation), or prevent leaching of contaminants in the first place (phytostabalization).
Perhaps if they had known where it would lead, the site workers at Oak Ridge might have been less frustrated when they finally found their answer.