Marker compound system

There are inherent problems associated with enzyme-mediated methods, regardless of the method used. The right conditions must be met, of course, for the enzyme action to take place. Unlike fluorochromes or gold particles (two other marker compounds), enzymes need to act chemically for the assay to work. Also, the enzyme action must only represent the marker molecule. Endogenous enzyme or enzyme-like activity can create problems only realized in systems that use enzymes. Also, the use of enzymes demands more attention to detail because of the increase in sensitivity that is often obtained. The problem of unwanted reactivity is enhanced in enzyme-mediated reactions more so than in others, in part because of the additional level of sensitivity brought about by the continuous action on a substrate. 

The complexity of the groundwater flow system is also seen by comparing the private well analyses with the private well profiles of Figure 8. This figure shows the best estimate of the depth of each well with respect to land-surface elevation. The marker compound... 

In the subsurface system, however, there is concern about concentrations of contaminant compounds in drinking water. Both shallow and deep wells have been found to contain the marker compound in this system. More information is needed to fully assess the various areas of the aquifer impacted to date and rates of transfer between them especially because changes can occur in aquifer systems when groundwater pumpage increases. The transport of residuals of these substances in flood plain and channel bottom sediments must be better understood to assess the nature of the release into ground and surface water in the future. 

A huge proportion of the presented investigations used organic marker compounds in order to differentiate the various anthropogenic emissions to the river and groundwater systems. The studies are not restricted to the application of established marker compounds, but numerous new marker substances were introduced and evaluated. 

The GC/MS non-target screening analyses revealed numerous compounds of which selected ones are subsequently presented and discussed in the following mainly with respect to their source specifity and their spatial distribution within the riverine system. Concentrations of anthropogenic marker compounds as well as of still unnoticed contaminants will effectively characterize anthropogenic emissions and provide a more detailed view on the pollution of the Lippe river. All quantitative data are shown in Tab. 2 a-d. 

The main focus of this study was to identify organic substances in Havel and Spree river sediments that could trace anthropogenic emissions of specific sources within the system. Therefore, selected contaminants with respect to their source specificity and to their environmental stability are discussed in order to characterize new potential anthropogenic marker compounds. 

Di- and trichlorinated benzenes were detected not only at sample sites mainly influenced by the Elbe river but also at sampling sites G and D, which are mainly influenced by input of the Ems river, with similar concentrations as in samples E and F (see Tab. 2). Hence these lower substituted compounds, which are used as synthetic raw material for many technical products such as antiseptic agents, solvents and additives (Biyant, 1993), are not appropriate marker compounds for tracing Elbe river derived contaminations. In contrast the tetra- to hexachlorinated benzenes, which have formerly been identified as contaminants in particulate matter of the Elbe river system (Schwarzbauer 1997, Schwarzbauer et al. 2001), appeared in the North Sea sediments only at sampling sites A,B,C,E and F (see Tab. 2). Fig. 1 illustrates the spatial distribution of hexachlorobenzene with concentrations between 2 and 50 pg/kg TOC in samples influenced by the Elbe river. 

Bis(4-chlorophenyl)-l,l,l-trichlorethane (DDT) and related substances were also detected in the North Sea sediments and were previously characterized as abundant compounds in the Elbe river system. They are only of minor use as marker substances because of their widespread occurrence in the aquatic environment (Schwarzbauer et al. 2000). However, DDT was applied in the Elbe river catchment area for a longer period of time than in regions affecting the Ems and Weser rivers. Hence, elevated concentrations were recently detected in Elbe river water and sediments (e.g., Goetz et al. 1994, Dannenberger and Lerz 1998, Ricking et al. 2003, Schulze et al. 2003) and, consequently, the application of DDT metabolites as Elbe specific marker compounds has to be reevaluated by quantitative analyses. 

The chemometric principle was used to derive a guideline for obtaining a simple yes or no answer about the sterility of food particulates heated at aseptic processing temperatures. A quadratic temperature pulse model was used to estimate bacterial destruction from the fractional yield of thermally produced chemical marker compounds (2,3-dihydro-3,5-dihydroxy-6-methyl-4(H)-pyran-4-one, M-1, and 4-hydroxy-5-methyl-3(2H)-furanone, M-2) and the rate constants and the activation energies of the chemical and bacterial systems. The model yielded a conservative estimate of lethality at the center of meat-balls heated under different time-temperature conditions. A scheme for determining the minimum marker yield for a designated F -value is provided. 

The identification and quantification of potentially cytotoxic carbonyl compounds (e.g. aldehydes such as pentanal, hexanal, traw-2-octenal and 4-hydroxy-/mAW-2-nonenal, and ketones such as propan- and hexan-2-ones) also serves as a useful marker of the oxidative deterioration of PUFAs in isolated biological samples and chemical model systems. One method developed utilizes HPLC coupled with spectrophotometric detection and involves precolumn derivatization of peroxidized PUFA-derived aldehydes and alternative carbonyl compounds with 2,4-DNPH followed by separation of the resulting chromophoric 2,4-dinitrophenylhydrazones on a reversed-phase column and spectrophotometric detection at a wavelength of378 nm. This method has a relatively high level of sensitivity, and has been successfully applied to the analysis of such products in rat hepatocytes and rat liver microsomal suspensions stimulated with carbon tetrachloride or ADP-iron complexes (Poli etui., 1985). 

---