Cleaning Superfund Sites

Jun 09, 2018 by Colin Thomas from Veterans Off-Grid in Sustainability
Landfills, despite common practice, are not environmentally friendly; however, there are more damaging ways to dispose of our garbage. For decades, various communities, corporations, and even the military have a similar habit of disposing of their toxic substances via burying them in a hole or dumping them into nearby lakes and rivers. The site is secured after the soil is contaminated, but when the water becomes polluted, it no longer facilitates aquatic life nor is it safe for us to drink. Areas deemed toxic enough to make clean up a priority by the EPA are called Superfund sites. The toxins typically found are heavy metals, like arsenic or mercury, though pesticides and radioactive materials also qualify. The EPA website lists nearly 2,000 Superfund sites solely within the United States.

Clean up is quite expensive because tons of soil must be excavated and treated before 30% of it can be returned to the site. The rest remains contained due to the toxins. Cleaning up toxic water is more expensive and challenging due to the mobile nature of water. Often it is a matter of speed, as workers must pump out the water faster than it flows to prevent the pollution from spreading further.

There are, however, alternative options for cleaning Superfund sites that deserve more attention such as a process called Phytoremediation. The idea is plants removing dangerous toxins from the soil without much human involvement. There are six methods of phytoremediation: (1) Phytodegradation, (2) Phytovolatilization, (3) Phytoextraction, (4) Phytostabilization, (5) Rhizodegradation, and (6) Rhizofiltration. Different toxins require different plants and different methods.
Phytodegradation is a method in which a plant absorbs toxins and destroys them or converts them into something less harmful.

Phytovolatilization is the process of a plant absorbing toxins and releasing them into the air as gases. Through Phytoextraction, plants take in toxins and house them in their cells. Phytostabilization is plants preventing the toxins from spreading through the ecosystem. In Rhizodegradation, the natural compounds put out by the roots of plants attract microorganisms that break down the toxins in the surrounding soil. Lastly, Rhizofiltration uses the roots of plants to filter water and extract its toxins.

The most straightforward methods are Phytodegradation and Rhizodegradation because the plant, a solution often practiced in homes, destroys the toxins. The other ways are just as effective, though they require a bit of monitoring such as in Phytovolatilization, as to prevent the air we breathe from accumulating dangerous levels of toxins. With Phytoextraction, the plants store the toxic chemicals in their roots blossoming into something else, or insects eat the leaves and reintroduce the toxins into the ecosystem. Once enough toxins are absorbed into the plant, it is easier to remove and incinerate vs. gathering and cleaning the polluted dirt. Interestingly enough, ash from toxic plants takes up less than 10% of the space leftover poisonous soil would consume if dug up!

This is not a perfect solution because the soil can become too toxic or the toxins are too deep for specialized plants. Many researchers are focusing on genetically modifying plants to remediate faster, but there are certain drawbacks to consider with GMOs. Another disadvantage is time. Depending on the plants used, the concentration of toxins, and climate of the Superfund site, clean up could take decades. Although, the land can still have use outside of development. Again, fruit and lumber is a possible product of phytoremediation plants, and parks can exist on the property during the phytoremediation process as long as certain precautions are taken. At the very least, a hill covered in trees and bushes is more attractive than a mound of garbage.

Note: Apart from the defined methods of phytoremediation, plants can provide some other exciting services worth mentioning. The first is hydraulic control. Even plants that do not use Rhizofiltration absorb water and transpire it. If contaminated water is in danger of seeping into drinking water, plants can be used to soak up the water and prevent its flow. Vegetative caps are another service I just alluded to. Instead of using plastic or clay to cover a landfill, plants can be used to prevent the escape of toxins. Past that, cover crops can be planted to avoid pesticides and soil from leaving the farm, rain gardens can cleanse parking lot runoff before it enters the ground, eco-machines can be used to treat wastewater and sewage, and houseplants can cleanse the air indoors.