Environmental forensic investigations typically need to be able to identify the source(s) of contamination, differentiate between potential sources and apportion liability, determine the enhancement above the background or the baseline condition, provide an age in the environment and estimate the potential impact on receptors. No two cases are the same and different approaches may be used each time although there are a number of tools that are frequently used. It is possible in the simpler scenarios to determine the presence of a particular unique chemical or biological marker for the source. However, this is a relative rare occurrence and it more usual to develop a more complex chemical signature based on several compounds rather than one. The challenge then becomes determining “how similar is similar?” and quantifying the contributions. This usually requires a range of multivariate statistical methods such as Partial Least Squares (PLS) when the source can be sampled or Polytopic Vector Analysis (PVA) when no such samples exist and reconstruction is required. The process of matching a source to an environmental sample may be made more complex by the partitioning between compounds due to a range of physical processes. Some compounds are more readily biodegraded which may complicate the attribution of source although it does provide the potential for determining the age in the environment. Careful selection of the appropriate compounds needed for each task is required and this should be considered at the sampling design stage. When chemicals are functionally identical (the same chemical but potentially from several sources), the use of stable isotopes can significantly assist in the investigation. The variability of the 18O and 2H content in meteoric water together with changes in the 13C from the “food source” and 15N from protein / fertilisers, can all assist in differentiating origin. Weathering processes will also tend to act more rapidly on the lighter fraction of the compound leaving the heavier fraction behind thus providing another estimate of age. As with all methods, there are a number of big caveats for each method and these also vary between cases. A number of examples will be presented including source identification of refine oil products, solvents in ground waters, discharged chemicals and air emissions.

Tool box for forensic investigations in the environment

2019 Fall National Meeting

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