Biodegradable, rendering

Nowadays, a strategic area of research is the development of polymers based on carbohydrates due to the worldwide focus on sustainable materials. Since the necessary multi-step synthesis of carbohydrate-based polymers is not economical for the production of commodity plastics, functionalization of synthetic polymers by carbohydrates has become a current subject of research. This aims to prepare new bioactive and biocompatible polymers capable of exerting a temporary therapeutic function. The large variety of methods of anchoring carbohydrates onto polymers as well as the current and potential applications of the functionalized polymers has been discussed recently in a critical review [171]. Of importance is that such modification renders not only functionality but also biodegradability to the synthetic polymers. 

Compared with tar, which has a relatively short lifetime in the marine environment, the residence times of plastic, glass and non-corrodible metallic debris are indefinite. Most plastic articles are fabricated from polyethylene, polystyrene or polyvinyl chloride. With molecular weights ranging to over 500,000, the only chemical reactivity of these polymers is derived from any residual unsaturation and, therefore, they are essentially inert chemically and photochemically. Further, since indigenous microflora lack the enzyme systems necessary to degrade most of these polymers, articles manufactured from them are highly resistant or virtually immune to biodegradation. That is, the properties that render plastics so durable... 

Polyaromatic hydrocarbons absorb strongly to humus and other soil components, rendering these contaminants difficult to remove by thermal, physical, or chemical means, and unavailable for biodegradation. To desorb polyaromatic hydrocarbons from soil, surfactant flooding processes and soil-washing processes or treatments to enhance the biodegradation of polyaromatic hydrocarbons have been considered. 

Diisopropyl methylphosphonate has not been shown to be amenable to biodegradation. Little if any degradation by indigenous bacteria occurred in soil "dosed" with radiolabelled diisopropyl methylphosphonate (Williams et al. 1989). Biodegradation by aquatic microorganisms has been shown to be equally ineffective (Spanggord et al. 1979 Van Voris et al. 1987), rendering it inappropriate as a means for the disposal of diisopropyl methylphosphonate. 

Ozone In-line Chemical oxidation will occur, rendering compounds more biodegradable Ozone generation is expensive Toxic to microorganisms except low concentrations... 

Adsorption is a physicochemical process whereby ionic and nonionic solutes become concentrated from solution at solid-liquid interfaces.3132 Adsorption and desorption are caused by interactions between and among molecules in solution and those in the structure of solid surfaces. Adsorption is a major mechanism affecting the mobility of heavy metals and toxic organic substances and is thus a major consideration when assessing transport. Because adsorption is usually fully or partly reversible (desorption), only rarely can it be considered a detoxification process for fate-assessment purposes. Although adsorption does not directly affect the toxicity of a substance, the substance may be rendered nontoxic by concurrent transformation processes such as hydrolysis and biodegradation. Many chemical and physical properties of both aqueous and solid phases affect adsorption, and the physical chemistry of the process itself is complex. For example, adsorption of one ion may result in desorption of another ion (known as ion exchange). 

Fig. 21.4. Transport of benzene within an aerobic aquifer, modeled in two dimensions. Contaminated water containing 1 mg kg-1 benzene leaks into the aquifer over the course of two years, at the point indicated. As in the previous model (Fig. 21.3), the benzene is retarded by sorption to organic matter in the aquifer and attenuates due to sorption, biodegradation, and dispersive mixing. Plots were rendered using the matlab software.

Toxic compounds are frequently rendered less toxic by electrochemical treatment, for instance dehalogenation of chlorinated derivatives such as PCBs or AOX (performed in a divided cell or in the absence of Cl ions in a monocell) odors are eliminated or greatly reduced, i.e. reduction of nitrotoluene which can be a serious odor nuisance biodegradability is improved. Elimination of colloids and surfactants is possible. 

The linker group that bridges the cationic lipid headgroup with the hydrocarbon moiety controls the biodegradability of a cationic amphiphile. Most of the linker bonds are ether, ester, or amide bonds (Fig. 1). Compounds with ether links generally render better transfection efficiency. However, they are more stable and may cause higher toxicity, while cationic lipids with ester links such as DOTAP are more biodegradable and less cytotoxic in cultured cells [28, 39]. Noteworthy,... 

Table 1 demonstrates the manner in which conjugating an enzyme to albumin renders it gieiuficantlv resistant to biodegradation either bv temoeratiire... 

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