DINING ON POLLUTION

Bacteria and other microorganisms have been digesting other creatures' waste products for millions of years. As a result, there are biological processes to break down most organic compounds, including the amazing variety of complex chemicals synthesized by plants. Some of these processes are now being exploited to break down the complex chemicals made by man. ''Bioremediation" is the name given to the use of biological processes to clean up contaminated soil or water.

Almost every organic compound synthesized by man can be broken down, albeit slowly, by microorganisms if their other needs for growth are met. Microorganisms need water, certain inorganic nutrients, and sometimes air to live, but once furnished with those staples, they will obligingly break down many of the synthetic organic chemicals mankind has created, used, and discarded. In fact, scientists have discovered that many toxic chemicals—such as drain cleaners, paint thinners, and used crankcase oil—are routinely broken down by microorganisms that live in wastewater treatment plants downstream.

Enzyme catalysts were used to clean up some of the beaches in Prince William Sound that were contaminated by oil in 1989. Cleanup crews added fertilizer to the beaches, stimulating the growth of their natural populations of microorganisms, which soaked up oil along with the fertilizer and catalyzed its degradation. Without fertilizer to help things along, the microbes would still have digested the oil, but at a very slow rate. The slow rates at which biological processes degrade pollutants such as spilled oil are one reason that bioremediation is not in more widespread use.

However, bioremediation is potentially the most cost-effective approach for cleaning up a contaminated site. Most sites contain a complex mixture of various chemicals. The array of native microorganisms, bolstered when necessary by laboratory cultures of specialized bugs for particularly intractable substances, would simultaneously catalyze the breakdown of the whole assortment of substances present at a site—an approach that could be far cheaper than the current practice of applying a sequence of physical and chemical treatments, each one tailored to particular contaminants. Bioremediation should be less invasive, leaving the soil in place during treatment rather than digging it up, and thus the site should recover more quickly afterward. The process is also self-perpetuating—the bugs will eat the pollutant indefinitely as long as the fertilizer holds out. Thus stimulating natural microorganisms and introducing laboratory-bred or even rationally designed organisms could result in the safe and effective remediation of a large number of contaminated sites across the country.



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