Identifying Background Concentrations

In Europe, the notion that it may be possible to determine a natural background concentration of a metal at most sites may be unrealistic. Many hundreds of years of industrial activity, urbanization, and widespread aerial deposition mean that it is best to consider background concentrations as those determined at sites of relatively low anthropogenic impact. These concentrations will still vary considerably from site to site due to geological influences. 

Similarly, in Canada the natural background is defined as that fraction of ambient metal considered to be dependent on the biogeochemistry of the site, in contrast to the fraction that reflects historical human activity. However, in some areas of the world, 

Environmental and Human Health Standards for Water and Soil 

We are not able to recommend any single approach for identification of background concentrations as preferable to the others. 

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In order to ensure effective land-use planning, geochemical sampling and mapping are required to identify areas where the natural background concentrations are elevated so that... 

Background concentrations of suspected or tentatively identified hazardous chemical contaminants may be extremely important in determining if an incident has occurred. In some cases, and for some hazardous chemicals, background levels may be at detectable concentrations. Baseline occurrence information is derived from monitoring data and is used to characterize typical levels of a particular chemical contaminant. 

The Student s t-test probability (TP) measures the geochemical contrast (essentially equivalent to precision) of an exploration method. This probability identifies the likelihood that anomalous and background concentrations, defined by a specific threshold, are derived from the same population by measuring the difference between the mean anomalous and background concentrations. The lower the TP e.g. the minimum TP for any threshold MTP), the more geochemical contrast and the more likely that random variations will not influence or change the results. 

Rose et al. (1979) discuss the concept of threshold, the upper limit of normal background fluctuations. Values above background are considered anomalous. This approach is directly applicable to contamination studies since a contaminated soil is an anomalous soil. The simplest way of identifying threshold concentrations is by collecting samples from apparently uncontaminated areas (eg, those remote from urban or industrial influences). After analysis the geometric means and deviations are calculated. The threshold is then the value lying two or more standard deviations from... 

Namral background concentrations for heavy metals can be identified by the nearly stable or constant values below the sediment depth, which represents about the change from the nineteenth to the twentieth century. A comparison of natural background values of the heavy metals Cu, Pb, Zn, Hg in different Baltic Sea Basins, based on the cores of this study and completed by former investigations (Brugmann, 1998), is given in Table 14.5. 

Field Blank The same matrix under investigation but not contaminated by the target analytes that are included in all sample preparatory procedures. Analysis of field blanks identifies the background concentration for the preparatory method as well as evaluating all interferences related to the matrix investigated. In this protocol, the analysis of field blank should be performed on uncontaminated... 

As for the mechanism of permeation through the endothelial luminal surface can be characterized by changing the background concentration of mother substances. When it is passive, concentration changes have no influence on but when a facilitated transport is involved, then raising concentration reduces the apparent PS. Facilitated transport has been identified for adenosine (Gorman et al., 1983). 

Emissions from five different excited electronic states of 02 throughout the visible spectral region of 400-800 nm have been identified [17], placing a practical limit on the concentration of O atoms that can be used as a chemiluminescence reagent since the background emission increases quadratically in O atom concentration. 

Since matrix and background effects are notoriously difficult to identify and control, quantitative XRF analysis usually entails the use of standards. One can write an expression relating the concentration of an analyte in a sample with the XRF intensity of one of its emission lines ... 

Significant process conditions preceding the incident should be identified, especially if the process is a batch operation or if there was any known deviation from normal conditions of sequences, flows, pressures, concentrations, temperatures, pH, or other process parameters. Often it is helpful to separate the background conditions into several distinct periods. One category may be normal conditions, a second category may be the time period from 48 hours up to 1 hour before the occurrence, and a third section may address the background immediately (1-20 minutes) before the occurrence. 

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