Environmental direct approach

The stated preference method is a direct approach and is used in order to value both use values and non-use values by using a hypothetical market. The choice experiment (CE) and the contingent valuation (CV) methods are the two most common examples of stated preference methods. In the CE method the respondents are asked to choose a level of environmental quality from a set of varying environmental qualities, called choice set. In the CV method the respondent is asked to imagine an environmental market situation and is then asked how she would act in that given situation. CE and CV attempts to find the WTP for a good or service by asking individuals direct questions about their preferences. Alternatively, researchers can ask the respondents for their WTA. 

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-... 

It should be clear that any partially direct approach (e.g., the use of predetermined lists of compounds) is not consistent with the complete and comprehensive requirements of either the direct or the phased environmental assessment philosophy and therefore is not an alternative to either approach. Similarly, a priori judgments based on process chemistry, thermodynamics, etc. are not acceptable practices in this context. 

One advantage of HPLC is that the analysis of unstable pesticides may be performed directly in aqueous medium without the extraction step or following extraction and concentration. Although the direct approach is quite useful for formulations or for kinetic studies to monitor the parent compounds in the presence of degradation products, its usefulness is limited in the case of environmental samples, where the concentration is usually in the parts-per-billion range (31). 

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... 

Platinum electrodes in conjunction with a reference electrode can be used to measure E values in environmental samples. However, these values cannot be considered definitive since they may represent a composite response of several redox couples and the actual response of the electrode can be limiting. A more direct approach is to measure the proportion of the oxidized and reduced components in a system and calculate Fh using the Nemst equation. Redox indicators [listed below with °(W)] may also be used as probes to assess redox status. Comparable to acid-base indicators, the color of these compounds changes when oxidized or reduced. With the exception of resomfin which is pink, the oxidized form of these compounds is blue while the reduced counterpart is yellow or colorless. 

This paper presents some basic background information about what molecular markers are, requirements for their use, and the types of applications that have been developed over the last 40 yr. Three case studies are offered as a means of illustrating some of the ways in which molecular markers can be used to answer specific environmental questions. These questions probably could not have been readily addressed using conventional environmental chemistry approaches. The objective of this paper is to stimulate interest in the molecular marker approach and to foster its use in environmental organic geochemistry. The interested reader is directed to Eganhouse (1997) for a more extensive discussion of molecular markers, their uses and limitations. 

In the late 1980s attempts were made in California to shift fuel use to methanol in order to capture the air quaHty benefits of the reduced photochemical reactivity of the emissions from methanol-fueled vehicles. Proposed legislation would mandate that some fraction of the sales of each vehicle manufacturer be capable of using methanol, and that fuel suppHers ensure that methanol was used in these vehicles. The legislation became a study of the California Advisory Board on Air QuaHty and Fuels. The report of the study recommended a broader approach to fuel quaHty and fuel choice that would define environmental objectives and allow the marketplace to determine which vehicle and fuel technologies were adequate to meet environmental objectives at lowest cost and maximum value to consumers. The report directed the California ARB to develop a regulatory approach that would preserve environmental objectives by using emissions standards that reflected the best potential of the cleanest fuels. 

In the United States, the Resource Conservation and Recovery Act of 1976 (RCRA) is the major legislation covering the disposal of solid and hazardous wastes (2). This act provides a multifaceted approach to solving the problems associated with the generation of approximately 5 billion metric tons of solid waste each year in the United States. It places particular emphasis on the regulation of hazardous wastes. This law established the Office of Solid Waste within the Environmental Protection Agency and directed the agency to publish hazardous waste characteristics and criteria. 

The solids that result from wastewater treatment may contain concentrated levels of contaminants that were originally contained in the wastewater. A great deal of concern must be directed to the proper disposal of these solids to protect environmental considerations. Failure to do this may result in a mere shifting of the original pollutants in the waste stream to the fmal disposal site where they may again become free to contaminate the environment and possibly place the public at risk. A more reasonable approach to ultimate solids disposal is to view the sludge... 

Thermal and catalytic incinerators, condensers, and adsorbers are the most common methods of abatement used, due to their ability to deal with a wide variety of emissions of organic compounds. The selection between destruction and recovery equipment is normally based on the feasibility of recovery, which relates directly to the cost and the concentration of organic compounds in the gas stream. The selection of a suitable technology depends on environmental and economical aspects, energy demand, and ease of installation as well as considerations of operating and maintenance. 7 he selection criteria may vary with companies or with individual process units however, the fundamental approach is the same. 

The approach to the evaluation of vibrational spectra described above is based on classical simulations for which quantum corrections are possible. The incorporation of quantum effects directly in simulations of large molecular systems is one of the most challenging areas in theoretical chemistry today. The development of quantum simulation methods is particularly important in the area of molecular spectroscopy for which quantum effects can be important and where the goal is to use simulations to help understand the structural and dynamical origins of changes in spectral lineshapes with environmental variables such as the temperature. The direct evaluation of quantum time- correlation functions for anharmonic systems is extremely difficult. Our initial approach to the evaluation of finite temperature anharmonic effects on vibrational lineshapes is derived from the fact that the moments of the vibrational lineshape spectrum can be expressed as functions of expectation values of positional and momentum operators. These expectation values can be evaluated using extremely efficient quantum Monte-Carlo techniques. The main points are summarized below. 

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