One-year measurements of chloroethenes in tree cores and groundwater at the SAP Mimoň Site, Northern Bohemia

Abstract

Chlorinated ethenes (CE) are among the most frequent contaminants of soil and groundwater in the Czech Republic. Because conventional methods of subsurface contamination investigation are costly and technically complicated, attention is directed on alternative and innovative field sampling methods. One promising method is sampling of tree cores (plugs of woody tissue extracted from a host tree). Volatile organic compounds can enter into the trunks and other tissues of trees through their root systems. An analysis of the tree core can thus serve as an indicator of the subsurface contamination. Four areas of interest were chosen at the experimental site with CE groundwater contamination and observed fluctuations in groundwater concentrations. CE concentrations in groundwater and tree cores were observed for a 1-year period. The aim was to determine how the CE concentrations in obtained tree core samples correlate with the level of contamination of groundwater. Other factors which can affect the transfer of contaminants from groundwater to wood were also monitored and evaluated (e.g., tree species and age, level of groundwater table, river flow in the nearby Ploučnice River, seasonal effects, and the effect of the remediation technology operation). Factors that may affect the concentration of CE in wood were identified. The groundwater table level, tree species, and the intensity of transpiration appeared to be the main factors within the framework of the experiment. Obtained values documented that the results of tree core analyses can be used to indicate the presence of CE in the subsurface. The results may also be helpful to identify the best sampling period for tree coring and to learn about the time it takes until tree core concentrations react to changes in groundwater conditions. Interval sampling of tree cores revealed possible preservation of the contaminant in the wood of trees.

Comparison of Phytoscreening and Direct‐Push‐Based Site Investigation at a Rural Megasite Contaminated with Chlorinated Ethenes

“…This behavior correlated well with groundwater level fluctuations (higher levels in winter), but other studies also point toward possible volatilization loss in summer due to high temperatures (e.g., Vroblesky ; Holm and Rotard ). The high monthly variations of concentrations in tree cores observed by Wittlingerova et al () do not indicate long‐term storage of chlorinated ethenes in wood. Model simulations (Trapp ) yield half‐lives for loss by volatilization from stems between three weeks (TCE, summer conditions) and about 3 months (PCE, winter) which means each tree core sample (typically between 5 and 10 cm in length) integrates the GW concentration of several weeks but most likely not over longer periods.…”

“…TCE may have been present in the volume available to the roots, but not in the samples taken by the DP sampling. Moreover, DP sampling relies on the concentration of contaminant present at the time of sampling, while trees integrate over weeks or even months (Trapp ; Wittlingerova et al ). The length of the tree cores was 5 cm, which is in agreement with recent suggestions (Holm et al ).…”

“…Compound concentrations in trees are reported to show seasonal variations and may also give indication on long‐term developments of subsurface contamination. Wittlingerova et al () monitored levels of chlorinated ethenes (mainly PCE and TCE) over a one‐year period and found lowest levels in summer and highest levels in autumn and early winter. This behavior correlated well with groundwater level fluctuations (higher levels in winter), but other studies also point toward possible volatilization loss in summer due to high temperatures (e.g., Vroblesky ; Holm and Rotard ).…”

Phytoscreening for Vinyl Chloride in Groundwater Discharging to a Stream

“…Phytoscreening studies have shown that concentrations of chlorinated ethenes in trees vary in all three dimensions (Vroblesky et al ; Holm and Rotard ; Limmer et al ). Further, seasonal variation in contaminant concentrations has been observed, where concentrations increased with increasing transpiration (Limmer et al ) and increasing groundwater level (Wittlingerova et al ). Transpiration is positively correlated with environmental conditions such as temperature and hours of sunshine, and negatively correlated with the relative air humidity (Stern ).…”

“…The lighter and less hydrophobic degradation products (Cwiertny and Scherer ) thus have a shorter residence time within the trees than the parent compounds. The best sampling time for detection of PCE and TCE in trees is after a period with high uptake of contaminated water and low diffusional loss from the tree due to decreased temperatures, resulting in high concentrations in the trees (Wittlingerova et al ). Since cis‐DCE and VC have considerable lower residence time in the tree trunk (the half‐times of loss from the stem are: PCE = 5.6d, TCE = 6.65d, cis‐DCE = 3.72d, and VC = 0.25d – calculated by the model of Trapp using the original parameters), their presence in wood is more likely to be dependent on uptake at the time of tree core sampling.…”