Widespread and persistent subsurface contamination by volatile organic compounds (VOCs) such as trichloroethene (TCE), tetrachloroethene (PCE), and benzene (BNZ) has been reported in most industrialized countries in the world. These compounds, particularly chlorinated VOCs (Cl-VOCs), can persist for decades in soils, sediments and aquifers. Extensive and expensive site investigations are generally required to characterize subsurface contamination by VOCs.

Studies have demonstrated that trees and other plants can absorb VOCs from the subsurface, a characteristic which is exploited for phytoremediation purposes. Trees exposed to organic chemicals in soils, sediments and water can take them up via the transpiration stream, sorption on roots, and gas diffusion into roots. Uptake varies with climate, soil organic matter and water content, plant characteristics (transpiration rate, root lipids content), and the contaminant's physical-chemical properties (especially octanol-water distribution coefficient; Kow).

Efforts have been made to use tree cores or branches to delineate subsurface contamination plumes, thereby reducing costs and the time involved in site characterization. Subsurface concentration, depth to groundwater, tree species, and in-tree dechlorination were all found to have a major impact on the concentration of chlorinated ethenes in tree cores.

To date, studies of VOCs in tree cores or branches have been conducted at sites of known subsurface contamination by Cl-VOCs. The current contribution was motivated by the possibility of using trees to detect unknown subsurface contamination sources of both Cl-VOCs and petroleum hydrocarbons, particularly in urban habitats. We term the proposed method 'phytoscreening'. In many urban centers, historical records on the location and activities of former industries frequently are missing or incomplete. As a result, a 'shotgun' approach to subsurface contaminant detection is required, the cost of which in large, populous areas can be prohibitive. Moreover, in highly urbanized settings, conventional screening methods involving the installation of monitoring wells or soil gas vapor probes are excessively complicated by the dense urban surface and subsurface infrastructure. To employ phytoscreening as an inexpensive, non-invasive tool for detecting unknown subsurface VOC contamination, the scope and limitations of the methodology need to be clearly defined. This was carried out by systematic tree core and subsurface sampling at two sites of known VOC contamination in an urban setting, one contaminated by Cl-VOCs and the other by petroleum hydrocarbons. Following this, the utility of phytoscreening for identifying sites of unknown subsurface VOC contamination in the Tel Aviv metropolis was tested.