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Soil Bioremediation

Instructor: Angela Hartsock

Angela has taught college Microbiology and has a doctoral degree in Microbiology.

Soil is a complex mixture of minerals and organic matter that supports a diverse array of life. Soil life is also capable of bioremediation. This lesson describes how soil acts to remove or neutralize environmental pollutants.

Bioremediation in Different Environments

Bioremediation is the use of biological processes to transform environmental contaminants into less toxic chemicals. The process of bioremediation is typically carried out by microscopic living organisms, like fungi and bacteria, but plants can also support bioremediation efforts by providing an ecosystem for fungi and bacteria or by immobilizing pollutants. Bioremediation can take place in a variety of different environments, each with their own unique challenges and benefits. Here we will look at how bioremediation takes place in soil and how humans can assist in this process.

Soil is not a Dirty Word

If you have ever talked negatively about soil, you really need to watch your mouth. Soil is a vital mix of minerals and organic material that supports the growth of a rich variety of plants and microorganisms. Soil supports the terrestrial ecosystems of our planet. A small handful of soil is absolutely teeming with life, including the obvious things like worms and insects as well as less obvious things like fungi and bacteria. For all the wonderful properties of soil, it is also easily contaminated by environmental pollutants released either intentionally through disposal or unintentionally through spills. Because soil is such a complex mixture of minerals and organic material it is not trivial to remove contaminants. Contaminants can end up sticking to other chemical compounds in the soil or they can move through soil along with rainfall, ending up in surface waterways or underground water reservoirs. So, cleanup of contaminated soil is important. And it just so happens that the soil itself is set up to assist us in this process.

A healthy soil seen in cross-section.
healthy soil cross-section

Bioremediation in Soils

Even without human intervention, the indigenous microorganisms living in soil can sometimes use contaminants for energy. Frequently, these microorganisms produce waste products that are less toxic than the original compound. When naturally occurring microorganisms are able to break down environmental contaminants without human intervention, we call this process natural attenuation.

However, soil conditions and things like temperature, pH, moisture, and nutrients fluctuate a lot and can either boost or limit the activity of the microorganisms attacking the contaminants. In some cases, we can aid the process of bioremediation by ensuring that the naturally occurring microorganisms have optimal conditions for their growth (or at least as close as we can get). We can aerate the soil to provide oxygen, add fertilizers or nutrients to support growth, add chemicals to adjust the pH, or add water to increase moisture content. When we boost microbial activity for bioremediation, this process is called biostimulation.

Finally, in some situations the naturally occurring microorganisms just aren't up to the job of bioremediation. In this case, if scientists have found a microorganism that is proven to break down the contaminant, that microorganism can be added to the environment to attack the pollutant. Bioaugmentation is the introduction of non-native microorganisms capable of detoxifying a contaminant. This of course relies on our ability to (1) find a microorganism that attacks the pollutant and (2) be able to grow the organism and add it to the soil environment where it's needed.

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