On-Line Biomonitors Used as a Tool for Toxicity Reduction Evaluation of in Situ Groundwater Remediation Techniques

Success of groundwater remediation is typically controlled via snapshot analysis of selected chemical substances or physical parameters. Biological parameters, i.e. ecotoxicological assays, are rarely employed. Hence the aim of the study was to develop a bioassay tool, which allows an on line monitoring of contaminated groundwater, as well as a toxicity reduction evaluation (TRE) of different remediation techniques in parallel and may furthermore be used as an additional tool for process control to supervise remediation techniques in a real time mode. Parallel testing of groundwater remediation techniques was accomplished for short and long time periods, by using the energy dependent luminescence of the bacterium Vibrio fischeri as biological monitoring parameter. One data point every hour for each remediation techniquewas generated by an automated biomonitor. The bacteria proved to be highly sensitive to the contaminated groundwater and the biomonitor showed a long standing time despite the highly corrosive groundwater present in Bitterfeld, Germany. The bacterial biomonitor is demonstrated to be a valuable tool for remediation success evaluation. Dose response relationships were generated for the six quantitatively dominant groundwater contaminants (2-chlortoluene, 1,2- and 1,4-dichlorobenzene, monochlorobenzene, ethylenbenzene and benzene). The concentrations of individual volatile organic chemicals (VOCs) could not explain the observed effects in the bacteria. An expected mixture toxicity was calculated for the six components using the concept of concentration addition. The calculated EC50 for the mixture was still one order of magnitude lower than the observed EC50 of the actual groundwater. The results pointed out that chemical analysis of the six most quantitative substances alone was not able to explain the effects observed with the bacteria. Thus chemical analysis alone may not be an adequate tool for remediation success evaluation in terms of toxicity reduction.

1. Introduction
The success of groundwater remediation is typically evaluated at the end of a remediation project by analysis of the concentrations of selected contaminants (Stefess, 1998). Contaminants are selected on the basis of their dominant concentration, because of their known toxicity to humans or other organisms or because of public awareness (Detzner et al., 1998). To our knowledge the progress of remediation is rarely controlled while the remediation is ongoing. Problems, like the partial or complete failure of the remediation might only be realized at the very end of the remediation project. Because chemical analysis will only detect the substances for which it is suitable, major toxicants might be overlooked or accidently ignored. Additionally, chemical analysis of a few selected substances alone is rarely a reliable tool to estimate the (eco-) toxicological effects of a complex contaminated environmental sample (Pedersen et al., 1998) and (Andersen et al., 1998). The toxicological effect of environmental samples very often may not be predicted by standard chemical analysis. In addition, contaminants which exert small toxic effects when applied singly might be highly toxic in combination with other contaminants (Faust et al., 2000a,b). Although a biotest detects the joint effect of all substances, contaminants or not, in an environmental sample, the use of biological tests alone will typically not provide specific informations about the actual toxic compounds causing the effects. Here, additional bioanalytical tools such as enzyme sensors detecting specific groups of substances could be helpful (Fennouh et al., 1997). In the view of remediation evaluation taking account of decontamination and detoxification the combination of chemical analysis and biological (i.e. ecotoxicological) tests might increase the explanatory power of both evaluation techniques (Brack et al., 1999).

Remediation effort might take months to years. Here, it would be rather laboriuous to regularily analyse biological effects to supervise toxicity reduction efficiency of the used remediation technique. On line analyses by automated systems could circumvent this problem.

To our knowledge only Van der Schalie et al. (2001) studied the effect of groundwater remediation in a real time manner. They used non-invasive real time monitoring of four physiological parameters derived from the ventilatory pattern of adult blue gills (Lepomis macrochirus). This research was based on the knowledge that coughing rate of fish is a sensitive tool to detect sublethal toxicities (Carlson and Drummond, 1977).

Groundwater in the region of Bitterfeld, Germany, is heavily contaminated due to a hundred year long history of chlorchemical industry. A recent integrative research initiative (SAFIRA) approached the contaminated groundwater on a regional scale in Bitterfeld aiming at developing new in situ groundwater remediation techniques (for details see (Weiss et al., 1998) and (Merkel et al., 2000). The remediation effort focussed to optimize the reduction of volatile organic groundwater contaminants like monochlorobenzene which reaches a maximum concentration of 25 mg l−1. The objective of the presented research project was to develop an automated on line biological monitor system to evaluate remediation success in a real time mode. This paper focusses on the establishment of an automated on line analysis of different groundwater remediation techniques using luminescent bacteria (Vibrio fischeri) as test organism for measuring bioenergetics. The luminescent bacteria (V. fischeri) were used as test organisms because toxicity data to various compounds are readily available (Kaiser and Palabrica, 1991) and the test with luminescent bacteria is a widely accepted and internationally standardized ecotoxicological biotest (Anonymous, 1998). Because several different remediation techniques are tested simultaneously, the automated biomonitor was adapted to supervise at least two different techniques at the same time. In this way it was possible to compare and evaluate the effectiveness of several remediation techniques. Beside efforts were undertaken, to identify the contaminants in the groundwater eliciting the observed toxic effects.

Objectives of this work therefore were to develop an automated biomonitor being used as: a tool for real time monitoring of different groundwater remediation techniques; a tool for assessing the effectiveness of remediation by means of toxicity reduction evaluation; a tool for process control; a tool for comparison of several different remediation techniques.

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