Unmixing Analysis: A Powerful Forensics Tool for Source Identification and Allocation
Integral scientists have developed software to apply a powerful but rarely used numerical technique to environmental investigations, in ways that provide a robust quantification of potential contributions of chemical sources at contaminated sites. Known as unmixing analysis, this mathematical technique has produced effective results by providing strong lines of evidence for estimating the relative contribution of different sources to site contaminants.
Initially developed as a technique to help unscramble mixed radio signals, unmixing analysis is still widely used in applications such as chromatograms, spectrographic data, and digital image analysis. In the past decade, the technique was adopted in fields ranging from investigations of ingredient mixtures in food products and fuel blends to face recognition and text mining. Unmixing analysis has recently received increasing attention from both regulators and industry in the environmental forensics field because of its ability to discriminate and quantify the nature and contributions of multiple sources to a site using standard environmental chemistry data sets.
Results from an unmixing analysis constitute a quantitative line of evidence for source allocation arguments, which are otherwise largely qualitative. From a set of samples containing complex mixtures of multiple chemicals, unmixing analysis produces information that can be used to determine the number and characteristics of different sources influencing those samples. The proportional contribution of each source to each sample is also accurately predicted. When sources have demonstrable characteristic chemical patterns, unmixing analysis can help identify the relative contributions of different sources, and of background conditions.
Integral has developed a software implementation of unmixing analysis and is using it to examine chemical mixtures in complex environments. In one recent application, unmixing analysis provided a strong line of evidence showing that the dioxins and furans from a former industrial facility were not the same as those impacting soils in neighboring residential yards. At another site, unmixing analysis was vital to estimating the relative contributions of two different shoreline sources of PCBs to marine sediments within a cleanup site.
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