11. BIOTRANSFORMATION

Biotransformation is the chemical alteration of compounds by living things. More precisely, it is the microbial alteration of xenobitics – the chemicals artificially made by humans.

Xenobiotic compounds often sequester in (adsorb to) soil. Although they disappear from the aquatic phase, they have not been degraded, they have merely concentrated into a phase (such as sediment) in which they are not very available for analysis or degradation. PCP, DDT, etc., have very long half lives because they are not bioavailable.

Fundamental knowledge of biodegradation and biotransformation mechanisms has already contributed significantly to improving the performance of bioremediation in the field. Bioremediation strategies employing co-metabolism, anaerobic bio-transformations of highly chlorinated solvents, and alternate electron acceptors which are in use today resulted in large part from fundamental investigations of the mechanisms used by microorganisms to transform contaminants. Despite the successful contributions of existing knowledge about biodegradation and biotransformation mechanisms, there is still much that research can contribute. At present, the understanding of biotransformation and biodegradation pathways and mechanisms in the field is incomplete. Although the degradation of many organics and the biotransformation of some inorganic compounds in laboratory cultures have been well described, it is unclear how this information relates to bioremediation processes under field conditions. In addition, research is needed to understand recently discovered biotransformation processes such as metal bio-transformations and bio-sequestration, coupled aerobic and anaerobic processes, co-metabolism, bio-transformations in the presence of alternative electron donors/acceptors, and bio-transformations catalyzed by consortia.

Why should we go for Biotransformation

In both the short and long term, a sound understanding of the fundamental mechanisms of biotransformation and detoxification will lead to improved prediction, control, and assessment of bioremediation performance, facilitate the selection and prioritization of contaminated sites for bioremediation, and result in the transfer of improved bioremediation processes for cleanup of contaminated sites.

Biotransformation is believed to be the dominant transformation process for 1,1-dichloroethene in groundwater, although this process is probably not important in aerobic surface waters. Biotransformation in soil has not been studied extensively, but it has been shown to occur by methanogenic organisms. Biotransformation will be more important in subsurface soils, because 1,1-dichloroethene in surface soils will volatilize to the atmosphere. 1,1-dichloroethene has been detected in air, surface water, groundwater, and soil, with the frequency of detection and the concentrations greatest near source areas (e.g., industrial areas, landfills, hazardous wastes sites).