"Phytoscreening": the use of trees for discovering subsurface contamination by VOCs.

We tested the possibility of using tree cores to detect unknown subsurface contamination by chlorinated volatile organic compounds (Cl-VOCs) and petroleum hydrocarbons, a method we term "phytoscreening". The scope and limitations of the method include the following: (i) a number of widespread Cl-VOC contaminants are readily found in tree cores, although those with very high vapor pressures or low boiling points may be absent; (ii) volatile petroleum hydrocarbons were notwell-expressed in tree cores; (iii) trees should be sampled during active evapotranspiration and from directions that are well exposed to sunlight; (iv) there is not necessarily a direct correlation between concentrations measured in tree cores and those in the subsurface; (v) detection of a contaminant in a tree core indicates that the subsurface is contaminated with the pollutant; (vi) many possible causes of false negatives may be predicted and avoided. We sampled trees at 13 random locations in the Tel Aviv metropolitan area and identified Cl-VOCs in tree coresfromthree locations. Subsequently, subsurface contamination at all three sites was confirmed. Phytoscreening is a simple, fast, noninvasive, and inexpensive screening method for detecting subsurface contamination, and is particularly useful in urban settings where conventional methods are difficult and expensive to employ.

Competitive uptake of trichloroethene and 1,1,1-trichloroethane by Eucalyptus camaldulensis seedlings and wood.

The efficient use of trees for taking up volatile organic compounds (VOCs) from the subsurface for remedial and screening purposes is hampered because many poorly quantified co-occurring processes affect VOC concentrations in the tree, the most basic of which are VOC sorption and uptake by roots. Toward understanding the dominant sorption mechanisms, uptake of trichloroethene (TCE) and 1,1,1-trichloroethane (TCA) by Eucalyptus camaldulensis seedlings was studied in both single-solute and bi-solute experiments. Single-solute and bi-solute sorption experiments on wood from a mature Eucalyptus camaldulensis specimen were also carried out. Competition between TCE and TCA for sorption sites was found in both seedling uptake and wood sorption experiments, indicating that partitioning is not the sole mechanism governing compound interactions in these systems. The nonlinear single-solute sorption isotherms on wood were fit by a dual-mode model including partitioning and Langmuir terms. The dual-mode model calculated parameters were consistent with the results of the bi-solute sorption experiments. As a consequence of competitive sorption processes, uptake of individual compounds may be lower than expected when multiple VOC contaminants are present in the subsurface.