Parameters affecting biodegradation

The initial species present, their relative concentrations, the induction of their enzymes, and their ability to acclimate once exposed to a chemical are likely to vary considerably, depending upon such environmental parameters as temperature, salinity, pH, oxygen concentration (aerobic or anaerobic), redox potential, concentration and nature of various substrates and nutrients, concentration of heavy metals (toxicity), and effects (synergistic and antagonistic) of associated microflora (Howard and Banerjee, 1984). Many of the parameters affect the biodegradation of chemicals in the environment as well as in biodegradation test systems used to simulate the environment. 

In this chapter, aromatic amines, sources and their environmental impact is outlined. The available methods for aromatic amines monitoring are described and degradation methods are reviewed, with special emphasis on biodegradation. Various parameters affecting the biodegradation, such as the type of electron acceptors, and some kinetic considerations are revised. 

Taking into account such environmentally representative experiments, it could be deduced that the extent of the biodegradation should not be affected by temperature, although this parameter clearly influences the rate at which this process takes place. In this respect, the lag phase is increased and oxidation of the LAS homologues (C11-C12) needs a longer time to develop at lower temperatures (see Fig. 5.3.7). The experiments performed previously at high concentrations and low temperatures may be affected predominantly by toxic effects, rather than by the particular temperature used. 

The interfacial microenvironment around a microbial community, that is the sum of the physical, chemical, and biological parameters which affect a microorganism, determines whether a particular microorganism will survive and/or metabolize. The occurrence and abundance of microorganisms in an environment are determined by nutrient availability, and various physicochemical factors such as pH, redox potential, temperature, and solid phase texture and moisture. Because a limitation imposed by any one of these factors can inhibit biodegradation, the cause of the persistence of a pollutant is sometimes difficult to pinpoint. The summary follows [39,92,94,97,109,110,172,173,176,189,190, 195,248-252,256-300]. 

Water quality parameters, such as pH, temperature, hardness, and salinity, can influence the effects of contaminants on aquatic life. The toxicity of TNT decreases slightly with increasing pH and temperature, but is not significantly affected by hardness [39], The persistence of TNT in the environment is limited, and several biological and physical processes (photolysis, hydrolysis) influence its environmental fate [39], The photolysis half-life of TNT appears to be season and latitude dependent, as it ranged from 14 h at latitude 20 in summer to 84 h at latitude 50 in winter in the northern hemisphere [40], The aquatic toxicity of several photo- and biodegradation products of TNT has been studied. Pink water obtained by constant illumination of a TNT solution was more toxic than the TNT solution to P. promelas using... 

Microbial activity must be prevented since it may lead to possible methyla-tion reactions, e.g. of inorganic antimony [16] or mercury species [54], and biodegradation, e.g. debutylation of tributyltin to monobutyltin [55]. Biological effects are generally dependent on the temperature. Therefore, it is necessary to control and monitor the temperature at which solutions are kept. The pH of the media is a parameter that strongly affects stability, mainly of inorganic species. 

Concentrations of PS at any point in the rhizosphere are determined by a number of different factors. Inputs of PS will vary depending on the Fe (and possibly other metal) status of the plant (Shi et al, 1988), the plant species and genotype (Romheld, 1991), the time of day (Takagi et al., 1984), the type of root (Bernards et al., 2002) and the age of the plant (Cakmak et al., 1998). Plant uptake, biodegradation, diffusion and adsorption to the soil solid phase will affect removal of PS from the rhizosphere. While we will discuss effective concentrations within the rhizosphere, the concentration of PS at any point in the rhizosphere will vary and depend on a numher of factors (Fig. 2). Thus, the PS-defmed rhizosphere can he thought of as being composed of four parameters ... 

The compound-specific data required for exposure assessments comprise the 1-octanol/water partition coefficient (log water solubility (S ), vapour pressure (p ), Henry s law constant (H, H ), soil sorption coefficient hydrolysis half-life time, photolysis half-life time and information on biodegradability (OECD, 1993c). These parameters generally relate to steady-state conditions - conditions that are rarely met in the real environment. The experimental data underlying the QSAR models are preferably determined by standardized protocols, but, even then, the absolute values are of variable reliability and precision, which clearly affects the accuracy of the predictions based on the acquired QSARs. The endpoints discussed in the following sections were selected because of their consideration in regulatory evaluation schemes in, for example, the EU (EEC, 1990). 

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