Testing of Biodegradability

Because of concern that chemicals may accumulate in the environment and may be detrimental to the health of the environment, United States Environmental Protection Agency (USEPA) has put the burden of proof on the manufacturers to show that their potentially dangerous chemicals are biodegradable within a reasonable amount of time without causing any harm to the environment. Toxic Substances Control Act of 1976 also authorized the US government to regulate the manufacture and distribution of potentially dangerous chemicals. A permission to produce toxic chemical by the industry will depend on biodegradability studies conducted by the industry at its own cost.

Biodegradability is generally tested by using pure culture of bacterium that is capable of degrading a toxic chemical in presence of test substance as the sole carbon source. This method is useful only to show that the test substance is biodegradable under controlled conditions, but one has to be careful drawing unrealistic conclusions as the conditions in the environment may differ largely from those in the laboratory. Some compounds may not be degraded by pure culture but are still amenable to degradation in the environment because of the presence of a complex microbial community and other easily uti-lizable carbon sources. On the other hand, a chemical that is degraded in pure culture may not be degraded in the environment. Some of the reasons why a toxic chemical may be degraded in pure culture and not in the environment are discussed under explanation of failure of bioremediation.

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