Rapid detection and delineation of contaminants in urban settings is critically important in protecting human health. Cores from trees growing above a plume of contaminated groundwater in Verl, Germany, were collected in 1 day, with subsequent analysis and plume mapping completed over several days. Solid-phase microextraction (SPME) analysis was applied to detect tetrachloroethene (PCE) and trichloroethene (TCE) to below nanogram/liter levels in the transpiration stream of the trees. The tree core concentrations showed a clear areal correlation to the distribution of PCE and TCE in the groundwater. Concentrations in tree cores were lower than the underlying groundwater, as anticipated; however, the tree core water retained the PCE:TCE signature of the underlying groundwater in the urban, populated area. The PCE:TCE ratio can indicate areas of differing degradation activity. Therefore, the phytoscreening analysis was capable not only of mapping the spatial distribution of groundwater contamination but also of delineating zones of potentially differing contaminant sources and degradation. The simplicity of tree coring and the ability to collect a large number of samples in a day with minimal disruption or property damage in the urban setting demonstrates that phytoscreening can be a powerful tool for gaining reconnaissance-level information on groundwater contaminated by chlorinated solvents. The use of SPME decreases the detection level considerably and increases the sensitivity of phytoscreening as an assessment, monitoring, and phytoforensic tool. With rapid, inexpensive, and noninvasive methods of detecting and delineating contaminants underlying homes, as in this case, human health can be better protected through screening of broader areas and with far faster response times.

Trees can take up and assimilate contaminants from the soil, subsurface, and groundwater. Contaminants in the transpiration stream can become bound or incorporated into the annual rings formed in trees of the temperate zones. The chemical analysis of precisely dated tree rings, called dendrochemistry, can be used to interpret past plant interactions with contaminants. This investigation demonstrates that dendrochemistry can be used to generate historical scenarios of past contamination of groundwater by chlorinated solvents at a site in Verl, Germany. Increment cores from trees at the Verl site were collected and analyzed by energy-dispersive X-ray fluorescence (EDXRF) line scanning. The EDXRF profiles showed four to six time periods where tree rings had anomalously high concentrations of chlorine (Cl) as an indicator of potential contamination by chlorinated solvents.

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The legal admissibility of scientific tools, such as dendrochemistry providing forensic evidence for criminal or civil cases, critically relies on the quality of fundamental and applied scientific research. The "Daubert" and "Frye" criteria that federal courts in the U.S.A use for determining legal admissibility requires publication of the scientific basis for the tool, and general acceptance by the scientific community. The field of dendroforensics is rapidly evolving, with new methods constantly being developed. In this manuscript we investigate how this dendrochemical evidence has been used successfully in the courtroom. The study of tree rings using physical anatomical and dendrochronological methods has been used as evidence in courts for over 150 years. From these beginnings in dendroecology dendrochemical and biological methods have matured enough to allow it to be used in forensic investigations, finding applications as a new independent line of evidence around the world, supporting cases involving murder, trafficking of protected species, and pollution crimes. We summarize some of the key applications of dendrochemistry in forensic cases and illustrate them with courtroom examples. The basic analytical methods discussed (e.g., PCR, GC-MS, LIBS, LA/ICP-MS, EDXRF) are all conventional. However, for findings to be relevant to judicial cases, the data is normally applied with additional lines of evidence gathered such as tree physiology and relevant statistics. This can allow us to gain more powerful data to help age date a specific event or to spatially identify a source material. The purpose of this article is to show how recent research has paved the way for the use of dendrochemical evidence in courts. It shows how dendrochemistry can be useful for forensic investigations including: murder cases, trafficking of protected species, and pollution crimes. The applications are illustrated by several summarized legal cases, but due to the confidential nature of some of these cases it was not always possible to provide full details or references.

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