Introduction

The environmental impact of organic aromatic pollutants mostly of anthropogenic origin is of increasing interest due to their persistency and often of serious effects on the environmental health. Many of these compounds represent industrial chemicals that were deliberately or inadvertently released into the environment. Others belong to undesired chemical by-products, personal care compounds or pharmaceuticals that resist against microbial or chemical processes, either during waste water treatment or in soil. Aromatic compounds are usually chemically resistant due to delocalization of energy and moreover environmental persistence of conjugated compounds has been suggested to be due to the dense clouds of Pi-electrons on both sides of the ring structures which make them scarcely susceptible to nucleophilic attack (Johnsen et al. 2005). The resistance is even more pronounced when the structures are substituted with so-called xenophores e.g., halogens (Alexander 1994). Some of the aromatic pollutants, for example polycyclic aromatic hydrocarbons and polychlorinated biphenyls, are characterized by low water solubility and high lipophility, resulting in their accumulation in fatty tissues of living organisms, including humans, and they are found at alarming levels in the food chain. Other compounds with higher water solubility as pharmaceuticals are transported by the movement of fresh waters and those with lipophilic character are often found accumulated in waste water treatment sludge or sediments (Cajthaml et al. 2009a). Semi-volatile or volatile compounds are transported over long distances in the atmosphere. Thus, both humans and

Laboratory of Environmental Biotechnology, Institute of Microbiology, v.v.i., Academy of Sciences of the Czech Republic, Videnska 1083, 142 20 Prague 4, Czech Republic e-mail: [email protected]

S. N. Singh (ed.), Microbial Degradation of Xenobiotics,

Environmental Science and Engineering, DOI: 10.1007/978-3-642-23789-8_11,

© Springer-Verlag Berlin Heidelberg 2012

environmental organisms are exposed to persistent aromatic pollutants around the world, in many cases for extended periods of time spanning generations, resulting in both acute and chronic toxic effects to both humans and wildlife. Generally, aromatic pollutants are distributed widespread in the environment; however, in most cases, their introduction into the environment can be restricted or minimized. Either they could be removed from sources of actual pollution or decontaminated from aged polluted sites found in many industrial areas across the globe. Decontamination-remediation methods are generally classified as physical, chemical and biological. The first two are referred to as engineering strategies, the latter as bioremediation. Bioremediation is often characterized as cost-effective and environmental friendly approach for the removal of contaminants from the environment. As cleanup tools, various types of organisms are employed, mainly microorganisms or plants. The bioremediation method has been established to exploit mostly bacterial and its limits have been repeatedly reviewed (Alexander 1994). There are several limiting factors that can significantly restrict successful bacterial application for biodegradation of especially aromatic pollutants present in the environment. The bacterial biodegradation of organopollutants is mainly performed by intracellular enzymes with high substrate specificity that results in limited availability of compounds with low water solubility. In bacterial degradation, these compounds are used as sources of carbon and energy, however, the process is active only above a certain concentration threshold. Moreover, genes responsible for organopollutant transformations are very often localized on plasmids. If the bacteria are not exposed to presence of the compounds for a longer time, the activity of the genes easily disappears. However, these impediments can be overcome by the application of fungi for degradation.

0 0

Post a comment