Xenobiotics: Sources, Pathways, Degradation, and Rish Associated with Major Emphasis on Pharmaceutical Compounds

Abstract

Xenobiotics are chemical substances which are alien or unnatural to the animal and human life. Xenobiotics include plant components, pharmaceutical drugs, pesticides, cosmetic products, added food flavors, fragrances, etc. At higher concentrations in environmental matrices, naturally occurring substances (endobiotics) may also be considered as xenobiotics. Xenobiotics are categorized as pesticides, pharmaceutical chemicals, personal care products, illicit narcotic drugs/substances, industrial/commercial goods, and nuclear waste and can be present in various environmental matrices. Xenobiotics are used by people and directly or indirectly penetrate in the different environmental matrices generating various metabolites and secondary products (some are even more toxic). Finally, plants, algae, and aquatic organisms take up xenobiotics leading to bioaccumulation, further causing biomagnification. One of the main obstacles to the sustainable water availability in urban systems is the presence of xenobiotics in aquatic ecosystems. In addition to the greater diversity of enzymes present in complex and varied community of microflora, the chemical distinctions between human and microbial transformations of ingested chemicals result from different selection processes that cause these activities. While host metabolism aids in the body’s elimination of xenobiotics, microbial changes to these substances and their human metabolites frequently promote microbial development by supplying nutrients or producing energy. The amount of xenobiotics found in environmental matrices can be varied from ng/L to g/L. In both humans and animals, long-term chronic exposure to even little doses of xenobiotics may cause toxic, mutagenic, carcinogenic, or teratogenic effects. These compounds may block the enzyme’s active site or affect it in an allosteric way. Some xenobiotics including chlordecone, dichlorodiphenyltrichloroethane (DDT), and dichlorodiphenyldichloroethylene (DDE) show tendency to bioaccumulate, and even their low-level chronic exposures can potentially have an adverse impact on cell signaling pathways. In order to create safer molecules for use in human environment, knowledge of enhanced molecular designs may be useful along with mechanism of xenobiotics’ action. The following chapter explores types and sources of various xenobiotics, the introduction of xenobiotics in the atmosphere and soil, pathways and migration in the soil and aquatic systems (with emphasis on pharmaceutical chemicals), and decomposition of pharmaceutical chemicals in the environment.