Biodegradation of Organic Pollutants

When people hear the term "organic," they may imagine something that is the opposite of pollution, but there are many substances derived from material with organic origins that are toxic. Petroleum is formed of ancient algae, but it releases benzene and toluene, both pollutants with adverse effects on environment and health. The list of other organic pollutants is long. Many pollutants can be transformed into benign materials using biological processes, or bioremediation.

Bacterial Biodegradation

• The U.S. Environmental Protection Agency describes bioremediation as "a treatability technology which uses biological activity to reduce the concentration and/or toxicity of a pollutant." This process is variously described as biotransformation or biodegradation. Bacteria figure prominently in this process, because they can break down toxic organic compounds at the molecular level, as an alternative to removing soil offsite to an expensive process of incineration and vitrification -- or trapping compounds inside solids.

Endophytic and Rhizospheric

• Soil polluted by toxic organic compounds can be remediated by degrading the pollutants using endophytic or rhizospheric bacteria. Endophytic bacteria are nonpathogenic bacteria that reside in plants; rhizospheric bacteria associate with plants around the root systems. Endophytic bacteria take compounds into the plants and accomplish biodegradation of some compounds; rhizospheric bacteria come into contact with pollutants directly in the soil. Untreated soil near plant roots contains more than 300 times the bacteria of soil without plant roots.

Poplars and Peas

• Endophytic biodegradation experiments have led to two very promising methods of soil remediation. In one method, researchers are using a hybrid poplar tree -- Populus deltoides X Populus nigra -- which contains methylotrophic endophytic bacterium, which has proven effective on volatile organic compounds -- like the benzene and toluene mentioned above -- and explosives residues. The other method is inoculating members of the pea family with Pseudomonas bacteria. These inoculated plants successfully broke down chlorinated organic herbicides.

The Roots of the Matter

• Petroleum and coal tar generate naphthalene, an organic toxic compound that is also found in mothballs. Naphthalene is damaging to plant roots; but experiments with Pseudomonas bacteria added to the rhizospheric ecosystem of grasses has thrived in that environment and appears to protect the roots from the effects of naphthalene. The perennial legume goat's rue has proven effective in the biodegradation of BTEX and other compounds deposited by oil and gasoline, through the rhizospheric activity of bacteria and fungi.