Environment, pesticides microbial degradation

Generally, pesticide residues will occur in the top 6 in. of the soil, which is also the region of greatest activity of soil fauna and flora. Thus, pesticides deposited in the soil are subject to various influences that affect their persistence in the environment. These include (1) soil type, (2) nature of the pesticide, (3) soil moisture, (4) soil pH, (5) soil temperature, and (6) microbial degradation of pesticides. 

Through microbial activities, a reducing environment can be created, particularly in a flooded soil. Many pesticides are degraded by reductive reactions that proceed nonenzymatically under anaerobic conditions. DDT, methoxychlor, and heptachlor readily break down in an anaerobic flooded ecosystem (Sethunathan, 1973). 

This chapter provides an overview of the analysis of TPs in the environment of three important classes of synthetic chemicals namely pesticides, human and veterinary pharmaceuticals, and personal care products (PPCPs). A series of analytical protocols applied to determine and analyze TPs of manmade chemicals originating from photolysis as well as from microbial degradation in the environment and wastewater treatment plants (WWTPs) is presented. Furthermore, strategies for identifying unknown TPs of xenobi-otic compounds including pesticides and PPCPs are presented based on the combination of mass spectrometric techniques and NMR, IR, and optical detection systems like DAD and FL. 

Pesticides are susceptible to a variety of transformations in the environment, including both chemical degradation and microbial metaboHsm. Microbial transformations are catalyzed exclusively by enzymes, whereas chemical transformations are mediated by a variety of organic and inorganic compounds. Many pesticide transformations can occur either chemically or biologically. Consequentiy, most pesticide dissipation studies include sterile treatments to... 

The microbial metabolic process is the major mechanism for the transformation of toxic organic chemicals in the subsurface environment. The transformation process may be the result of a primary metabolic reaction, when the organic molecule is degraded by a direct microbial metabolism. Alternatively, the transformation process may be an indirect, secondary effect of the microbial population on the chemical and physical properties of the subsurface constituents. Bollag and Liu (1990), considering behavior of pesticides, defined five basic processes involved in microbially mediated transformation of toxic organic molecules in the soil upper layer environment. These processes are described next. 

Walker, W.W., Stojanovic, B J. (1973) Microbial versus chemical degradation of malathion in soil. J. Environ. Qual. 2, 229-232. Wang, T.C., Hoffman, M.E. (1991) Degradation of organophosphorus pesticides in coastal water. J. Assoc. Off. Anal. Chem. 74(5), 883-886. 

The bioaugmentation strategy involves the selection of adapted microbial strains that metabolize a pesticide as a carbon or nutrient source. Under these circumstances, the rate of degradation is enhanced compared to the rate normally observed in soil or water. The development of an adapted microbial strain usually begins with the enrichment and isolation of pesticide-degraders from the contaminated environment. Enrichment is relatively easy with compounds that are used as carbon or nutrient sources. Compounds that are not readily utilizable, however, require novel approaches to enrich and isolate potential degraders, which may be manipulated to enhance their degradative capabilities. 

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