Bioremediation | Research & Encyclopedia Articles

The word "bioremediation" was coined by scientists in the early 1980s as a term to describe the use of microorganisms to clean polluted soils and waters. The prefix bio defined the process as biological, that is, carried out by living organisms. The noun remediation defined the process as one that resultedin the cleaning, or remediation, of the environment, via complete degradation, sequestration, or removal of the toxic pollutants as the result of microbial activity. Degradation means that the microorganisms decompose the pollutants to harmless natural products such as carbon dioxide (CO₂), water (H₂ O), or other nontoxic naturally occurring compounds. Sequestration means that the pollutant is trapped or changed in a way that makes it nontoxic or unavailable to biological systems. Removal means that while the pollutant is not necessarily degraded, the microbes physically remove it from the soil or water so that it can be collected and disposed of safely.

The principal goal of bioremediation is to return polluted environments to their natural state. Examples of the many contaminants that are amenable to bioremediation via degradation include organic chemicals such as pesticides, insecticides, herbicides, and pollutants derived from petroleum as the result of oil or fuel spills, or oil refining activities. Research in the 1990s has shown that even synthetic chemicals previously thought to be totally resistant to degradation, such as the insecticide DDT or the explosive TNT, are, in fact, degradable by microorganisms when they are supplied the right growth conditions. Examples of pollutants that can be sequestered or removed by microorganisms include toxic heavy metals such as lead (Pb), cadmium (Cd), and arsenic (As), and radioactive metals such as uranium (U). Toxic levels of metals are found in soils or waters previously contaminated as the result of military, industrial, or mining activities. Metals are found in various chemical forms, but unlike organic compounds, metals cannot be degraded. They can be changed only to some other chemical form. Therefore, the goal of metal bioremediation is to use microbes to change the metals into a form that is either sequestered in the soil in an insoluble form, or changed into a soluble form that can be removed from the soil with water, and then recovered later.

Various processes are used to carry out bioremediation. They include ex situ techniques, where contaminated soil is excavated, bioremediated in a vessel or pile, and then returned to the environment. Alternatively, within situ techniques, the contamination is treated where it occurred. This approach is particularly suited to treating contaminated groundwater in deep aquifers. Bioremediation can involve the inoculation of a contaminated environment with the specific microorganisms needed to carry out the bioremediation, or supplementation of the environment with nutrients that will promote the activity of microbes already naturally present. When supplementation is done in situ, it is sometimes called naturally accelerated bioremediation. The microorganisms naturally present in some contaminated environments may sometimes slowly bioremediate that environment without any human intervention. This type of bioremediation is called natural attenuation, a process that usually occurs very slowly over many years. Because it is effective and affordable, bioremediation is often the method of choice for cleaning polluted soils, groundwaters, aquatic areas, wetlands, and other environments.

Phytoremediation uses plants to remove both soilborne and waterborne pollutants. It is proving especially useful for treating heavy metal contamination, an exceptionally difficult type of cleanup job. Plants need soil nutrients and are efficient absorbers of all kinds of minerals. Some species, called hyper-accumulators, can concentrate metals thousand of times above normal levels. Indian mustard (Brassica juncea) will hyperaccumulate lead, chromium, cadmium, nickel, selenium, zinc, copper, cesium, and strontium. Detoxifying the soil is as simple as harvesting the plants.

Human Impacts; Soil, Chemistry Of.

Chaudhry, G. Rasul, ed. Biological Degradation and Bioremediation of Toxic Chemicals. Portland, OR: Dioscorides Press, 1994.

Crawford, Ronald L., and Don L. Crawford, eds. Bioremediation: Principles and Applications. New York: Cambridge University Press, 1996.

Quensen, J. F., S. A. Mueller, M. K. Jain, and J. M. Tiedje. "Reductive Dechlorination of DDE to DDMU in Marine Sediment Microcosms." Science 280 (1998): 722-24.

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