Biologically mediated transformations

2 General differences between major groups of organisms 

In Section 5.2 the chemotaxonomic application of some compound groups is examined in a little more detail, but first it is useful to consider some of the variations that can occur in the lipid constituents of individual organisms. 

Lipid content varies with tissue type within organisms and so the degree to which different tissues are preserved can be important. For example, 18 1 and 18 2 account for e.7 5% of the fatty acids in the beans of soya plants, whereas its leaves contain only c.20% of these 

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We examine two groups of contaminants that exhibit biologically mediated transformation in the subsurface petroleum hydrocarbons and pesticides. Both aerobic and anaerobic pathways for their biodegradation are considered. 

Crop protection chemicals are an important group of contaminants that exhibit biologically mediated transformation in aerobic or anaerobic subsurface environments. We consider two well-known contaminants the insecticide parathion, which is an organophosphate compound, and the herbicide atrazine, from the triazine group. 

The persistence (half-life) of atrazine in the subsurface is governed by chemically and biologically mediated transformations. Because the solubility of atrazine is relatively high ( 30mg/L) compared to its toxicity level in water (5 Lig/L), atrazine has become a hazard to groundwater quality. Atrazine has been detected in groundwater more than any other crop protection chemical two examples of atrazine persistence-transformation in aquifer environments are discussed next. 

In the last decade the case of methylmercury pollution has demonstrated the profound importance of understanding biologically mediated transformation reactions that produce organometallic compounds with a high potential for bioaccumulation and toxicity. 

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