Environmental phased approach

Two clearly distinct strategies to an environmental assessment sampling and analysis program that satisfy the requirements for comprehensive information are the direct and phased approaches. In a direct approach, all streams would be carefully sampled and the samples subjected to complete, detailed analysis using compound specific analytical techniques. In a phased approach, all streams would first be sur-... 

The procedures selected initially have been constantly improved in detail however, no significant changes in the basic techniques have been necessary. The phased approach is, therefore, a viable and cost effective concept for identifying potential environmental problems associated with discharge from industrial and energy processes. 

A complete environmental risk assessment, including extensive biological and analytical measurements, is not always required. Chapter 3 describes a phased approach developed for environmental assessments. 

There are few methods which can measure well-defined metal fractions with sufficient sensitivity for direct use with environmental samples (approach B in Fig. 8.2). Nevertheless, this approach is necessary in the experimental determination of the distribution of compounds that are labile with respect to the time scales of the analytical method. Recent literature indicates that high-performance liquid (HPLC) and gas chromatographic (GC) based techniques may have such capabilities (Batley and Low, 1989 Chau and Wong, 1989 van Loon and Barefoot, 1992 Kitazume et al, 1993 Rottmann and Heumann, 1994 Baxter and Freeh, 1995 Szpunar-Lobinska et al, 1995 Ellis and Roberts, 1997 Vogl and Heumann, 1998). The ability to vary both the stationary and mobile phases, in conjunction with suitable detector selection (e.g. ICP-MS), provides considerable discriminatory power. HPLC is the superior method GC has the disadvantage that species normally need to be derivatised to volatile forms prior to analysis. Capillary electrophoresis also shows promise as a metal speciation tool its main advantage is the absence of potential equilibria perturbation, interactions... 

The purpose of individual site assessment4 is to decide whether or not a site poses actual or potential risks to human health or the environment . A phased approach is recommended in accordance with recent guidance on environmental risk assessment and management.5... 

Figure 1. A phased approach for evaluating mutagenesis and presumptive carcinogenesis of environmental chemicals...

MicroChannel Enzyme Reactor. Enzymatic conversion is receiving attention because it is an environmentally friendly approach to synthesizing chemicals. Reactions can be carried out enzymatically in the solution phase or by immobilizing enzymes on microfluidic walls. The use of the latter type of reaction has the same mass and heat transfer advantages as the use of a microfluidic synthetic reactor. More information can be found in a published review article [6] and in the article microfluidic bioreactors in this encyclopedia. 

Environmental phase distributions of elements or inorganic chemicals usually involve different chemical species and therefore speciation reactions. For example, different species of an element such as mercury have different vapor pressure and solubility. Elemental mercury, Hg(0), is fairly volatile and only sparingly soluble in water, whereas oxidized Hg(II) complexes are much less volatile but more water soluble. The distribution of mercury among the phases of air, water, and solid will thus depend on its speciation, which in turn is influenced by variable conditions of the environment, including pH, redox conditions, and the presence of other chemical species. This is approached quantitatively using equilibrium reaction constants for the various speciation reactions and illustrated using distribution diagrams that delineate the major prevalent species as a function of pH or pE, or both. 

Multimedia models can describe the distribution of a chemical between environmental compartments in a state of equilibrium. Equilibrium concentrations in different environmental compartments following the release of defined quantities of pollutant may be estimated by using distribution coefficients such as and H s (see Section 3.1). An alternative approach is to use fugacity (f) as a descriptor of chemical quantity (Mackay 1991). Fugacity has been defined as fhe fendency of a chemical to escape from one phase to another, and has the same units as pressure. When a chemical reaches equilibrium in a multimedia system, all phases should have the same fugacity. It is usually linearly related to concentration (C) as follows ... 

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