Chemical Fingerprinting for Litigation Support - A Case Study of Effective Environmental Forensics. T. C. Bernhardt, A. K. Madl, K. A. Exuzides, and P. J. Sheehan, Exponent, Menlo Park, CA
In a class action suit, residents in the vicinity of a former pesticide reformulation and packaging facility had expressed health concerns over potential exposure to chemicals historically reformulated and/or handled at the facility. As part of an evaluation of the potential human health risks associated with exposure to residential soils, a surface soil sampling plan was designed to evaluate whether residential lot soil was contaminated and, if so, whether the facility was the likely source of chemical contamination. Soil samples were collected from plaintiffs’ lots and from areas at a substantial distance from the site (background reference areas). The results of the sampling investigation were screened against regulatory criteria for potential human health risks and used in conjunction with historical site data to evaluate the site as the probable source of contamination. A statistical evaluation of the data indicated statistically significant differences between the concentrations of all pesticides and metals at residential lots and those measured at the former facility. With the exception of DDE and DDT, no statistically significant differences were observed between chemical concentrations in residential lot and background reference soils. Principal components analysis (PCA) and polytopic vector analysis (PVA), conducted to assess the similarities in concentration patterns of selected pesticides in site and residential lot soils, demonstrated distinctly different chemical "fingerprints" for site and residential lot samples. These findings, combined with a lack of distinctive spatial concentration patterns expected from wind deposition from a source, suggest that the site was not the likely source of pesticides in residential lot soils.
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