Lipophilic xenobiotics bioaccumulation

Chlorinated micropoUutants are harmful for man and environment due to their toxicity, persistence, and bioaccumulation. Persistent compounds are very stable and difficult to get metabolized and mineralized by biological and chemical processes in the environment, and as a result, they have become ubiquitous in water, sediments, and the atmosphere bioaccumulation is the result of the lipophilicity of these compounds. Polychlorinated dibenzodioxins and -furans (PCDD/F) are not produced purposely like many of other chlorinated technical products, such as chlorinated biocides DDT, lindane, and toxaphene. The production and use of persistent organic pollutants (POPs), the dirty dozen has now been banned worldwide by the Stockholm protocol. It should be mentioned that about 3000 halogenated products have now been isolated as natural products in plants, microorganisms, and animals," but the total amount of these products is much smaller compared to xenobiotics. 

Bioaccumulation The accumulation of xenobiotic substances in organisms and the food chain is important in the assessment of the harmfiilness of a substance in the environment. The accumulation of organic substances in organisms occurs often in accordance with their lipophilicity (Figure 9.29) A ow often serves as a measure of lipophilicity and as a predictive parameter for bioaccumulation in the food chain. One also speaks of biomagnification to describe progressive accumulation of xenobiotic substances in the food chain. 

A great deal can occur to a xenobiotic between its introduction to the environment and its interaction at the site of action. Many materials are altered in specific ways depending upon the particular chemical characteristics of the environment. Bioaccumulation, the increase in concentration of a chemical in tissue compared to the environment, often occurs with materials that are more soluble in lipids and organics (lipophilic) than in water (hydrophilic). Compounds are often transformed into other materials by the various metabolic systems that reduce or alter the toxicity of materials introduced to the body. This process is biotransformation. Biodegradation is the... 

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