Removal, from toxic environment

Biologically available organic contaminants may find their way into the food chain and be toxic, but they are also more easily decomposed and are thus removed from the environment. Slowly decomposed biologically available organic compounds, such as pesticides, may have long lifetimes in soil and thus pose a hazard to animals and humans. Biologically unavailable compounds, such as tars, produce undesirable characteristics in soil, such as water... 

As briefly discussed, microorganisms can decrease metal toxicity by the oxidation or reduction of metals. Some microorganisms actively reduce metals to decrease bioavailability while others may oxidize metals to facilitate their removal from the environment. Early laboratory studies by Konetzka (1977) found Pseudomonas spp. 

It is understood that the concept of fugacity can be potentially very useful in identifying the static and dynamic behavior of toxic substances in the environment. Phenomena such as bioaccumulation becomes readily understandable and predictable. Also, it is valuable in assisting in the elucidation of the dominant process responsible for a substance s degradation or removal from the environment, and in identifying the signiHcant transfer process. 

In further studies, Roberts et al. [108] showed that 2.4nm polysugar-stabilized-Pd nanoparticles catalyzed the hydrodechlorination of trichloroethylene, an extremely difficult pollutant to remove from the environment. Mertens and coworkers recently reported a new approach for degradation of the toxic pesticide Undane (y-hexachlorocydohexane y-HCH) through a dechlorination process catalyzed by Pd nanoparticles [109]. A heterogeneous catalyst was used in which colloidal Pd nanoparticles were immobilized onto the biomass of ShewaneUa onddensis. The results showed that, upon interaction with the Pd nanoparticles, the dechlorination of lindane in water in a membrane reactor was highly effective. Indeed, when compared to a commercially available, powdered Pd(0) material, the immobilized Pd nanoparticles showed a high catalytic activity in the dechlorination of y-HCH. 

Lubricating Oil Extraction. Aromatics are removed from lubricating oils to improve viscosity and chemical stabihty (see Lubrication and lubricants). The solvents used are furfural, phenol, and Hquid sulfur dioxide. The latter two solvents are undesirable owing to concerns over toxicity and the environment and most newer plants are adopting furfural processes (see Furan derivatives). A useful comparison of the various processes is available (219). 

Bioremediation- Use of microorganisms to remove or detoxify toxic or unwanted chemicals from an environment. 

The selection of these compounds was made on the grounds of their toxicity, environmental stability, and tendency to undergo biomagnification the intention was to move toward their removal from the natural environment. In the REACH proposals of the European Commission (EC published in 2003), a similar list of 12 POPs was drawn up, the only differences being the inclusion of hexachlorobiphenyl and chlordecone, and the exclusion of the by-products, dioxins, and furans. The objective of the EC directive is to ban the manufacture or marketing of these substances. It is interesting that no fewer than eight of these compounds, which are featured on both lists, are insecticides. 

Salt, D.E., Blaylock, M., Nanda Kumar, P.B.A., Dushenkov, V., Ensley, B.D., Chet, I. and Raskin, I., Phytoremediation A novel strategy for the removal of toxic metals from the environment using plants, Biotechnology, 13, 468-474, 1995. 

The mobility of arsenic compounds in soils is affected by sorp-tion/desorption on/from soil components or co-precipitation with metal ions. The importance of oxides (mainly Fe-oxides) in controlling the mobility and concentration of arsenic in natural environments has been studied for a long time (Livesey and Huang 1981 Frankenberger 2002 and references there in Smedley and Kinniburgh 2002). Because the elements which correlate best with arsenic in soils and sediments are iron, aluminum and manganese, the use of Fe salts (as well as Al and Mn salts) is a common practice in water treatment for the removal of arsenic. The coprecipitation of arsenic with ferric or aluminum hydroxide has been a practical and effective technique to remove this toxic element from polluted waters... 

The removal of dyes from industry effluents is desirable not only for aesthetic reasons but also because azo dyes and their breakdown products are toxic to aquatic life and mutagenic to humans [8,9]. Without adequate treatment these azo dyes are stable and can remain in the environment for an extended period of time. Consequently, azo dyes have to be removed from wastewaters before discharge. 

It is often assumed that if something is in the soil, it will be in plants. This is incorrect. Plants do not take up all of the elements or molecules present in their immediate environment. However, there are some plants, called hyperaccumulators, that accumulate higher than normal levels of some toxic elements. These plants still do not take up all the elements in their environment and they are often small, so the total amount of toxic elements removed from soil is limited. In addition, not all species of an element are toxic and some are not biologically available and thus do not enter biological systems. For example, chromium as Cr(VI) is more toxic and more biologically available than is Cr(IH) [1]. 

Our questions broadened to consider how the transport and metabolic capabilities of these aquatic species compare with those of mammalian species. One reason for asking such a question is to assess whether the presence or absence of these capabilities alters the ability of fish to survive in toxic environments. Survival mechanisms fall into two catagories - behavioral and physiologic. An example of a behavioral mechanism could be as simple as a fish avoiding that area of a stream which contains toxic quantitites of phenol. When external perturbations caused by pollutants are small, homeostatic mechanisms such as those of the liver and kidney, allow fish to adapt to the body of water in which they exist. The problem then is related to defining the limits to which homeostatic phenomena can be stressed in aquatic species. An important reason to establish such information in fish is that bodies of water are the "ultimate sink" for a number of pollutants (12). Thus, while a behavioral response such as removing itself from a toxic environment is invariably available to a mammalian species, this type of response is impossible for a fish if a toxic xenobiotic occurs uniformly throughout an entire body of water. 

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