Biological transformation processes

Descriptions of the Major Types of Biological Transformation Processes... 

Bollag J-M, Liu S-Y (1990) Biological transformation processes of pesticides. In Cheng HH (ed) Pesticides in the soil environment processes, Impacts and Modeling. Soil Science Society of America, Madison, Wisconsin, pp 169-211. 

Bollag, J.-M. and S.-Y. Liu. Biological transformation processes of pesticides in Pesticides in the Soil Environment Processes, Impacts, and Modeling, SSSA Book Series 2, Cheng, H.H., Ed. (Madison, WI Soil Science of America, Inc., 1990), pp. 169-211. 

We have chosen to follow Watts [24] and discuss chemical and biological transformation processes in the same section. Watts notes that, although this approach is somewhat nontraditional, it is advantageous in that understanding of the abiotic chemical reactions serves as a conceptual basis for understanding the biochemical reactions (which are essentially the same except for the fact that the biochemical reactions are mediated by microorganisms). Where a reaction is predominantly abiotic or biotic, it will be noted in the discussion. In this section, the fundamentals of each chemical or biological reaction will be discussed, and model formulations for the reaction kinetics presented. 

In soil, ammonia may either volatilize to the atmosphere, adsorb to soil, or undergo microbial transformation to nitrate or nitrite anions. Uptake by plants can also be a significant fate process. Ammonia at natural concentrations in soil is not believed to have a very long half-life. If ammonia is distributed to soil in large concentrations, the natural biological transformation processes can be overwhelmed, and the environmental fate of ammonia will become dependent upon the physical and chemical properties of ammonia, until the ammonia concentration returns to background levels. 

Fig. 12-1 Biological transformations of nitrogen compounds. The numbers refer to processes described in the text.

Even if organocatalysis is a common activation process in biological transformations, this concept has only recently been developed for chemical applications. During the last decade, achiral ureas and thioureas have been used in allylation reactions [146], the Bayhs-Hillman reaction [147] and the Claisen rearrangement [148]. Chiral organocatalysis can be achieved with optically active ureas and thioureas for asymmetric C - C bond-forming reactions such as the Strecker reaction (Sect. 5.1), Mannich reactions (Sect. 5.2), phosphorylation reactions (Sect. 5.3), Michael reactions (Sect. 5.4) and Diels-Alder cyclisations (Sect. 5.6). Finally, deprotonated chiral thioureas were used as chiral bases (Sect. 5.7). 

The biological cycle — that may encompass processes of biological transformation, plant uptake, bioaccumulation, soil organisms transformations and others. 

In all of the workshops, but especially in the FAT and Exposure Assessment workshops, the need for better understanding and model representation of soil systems, including both unsaturated and saturated zones, was evident. This included the entire range of processes shown in Table II, i.e., transport, chemical and biological transformations, and intermedia transfers by sorption/desorption and volatilization. In fact, the Exposure Assessment workshop (Level II) listed biological degradation processes as a major research priority for both soil and water systems, since current understanding in both systems must be improved for site-specific assessments. 

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