Effect of radial directional dependences and rainwater influence on CVOC concentrations in tree core and birch sap samples taken for phytoscreening using HS-SPME-GC/MS.

Phytoscreening for chlorinated volatile organic compounds (CVOC) in tree core samples is influenced by many factors. For instance, greater fluctuations are observed for CVOC concentrations in samples taken around the trunk at a fixed height compared to samples taken directly next to each other. To avoid false negatives and inaccurate interpretation of the results, we investigated this radial directional dependence as well as the influence of rainwater on measured concentrations. CVOC analysis was performed by gas chromatography/mass spectrometry (GC/MS) following Solid-Phase-Microextraction (SPME). Phytoscreening was successfully carried out at three sites using this method. In addition, sap samples were taken from white birches during their budding period as a novel phytoscreening approach. Birch sap sampling is shown to be a suitable means of characterizing contaminant distribution within the soil subsurface. Radial directional dependence of CVOC concentrations varies by almost 80% for tree core samples and 50% for birch sap samples. Variations in concentrations measured around the trunk do not, however, provide information on the inflow direction of contaminated groundwater. The weather conditions were shown to have a greater influence so that CVOC concentrations measured from samples taken during colder, rainier weather were, on average, a factor of 100 lower than those taken during a warm and dry period. Nevertheless phytoscreening is adequate for CVOC characterization in the soil subsurface if the campaign is carried out during a dry weather period, the results then can be taken as being semiquantitative.