Algal ecotoxicological testing of groundwater priority contaminants using closed-system technique

While toxicity testing should be an integral part of the groundwater bioremediation projects, only few studies have attempted to include ecotoxicological tests, since standard testing procedures have not been developed to suit some of the groundwater priority contaminants. In fact, volatile organic compounds (VOCs), such as chlorinated aliphatic hydrocarbons (CAHs), belong to the most frequently found contaminants in European groundwaters. The development of a sensitive ecotoxicological procedure being appropriate for VOCs while relatively easy to be performed is therefore regarded as a current research need. With this aim, an algal test procedure has been set-up within a bioremediation project aimed at the evaluation of the efficiency of a bioelectrochemical technique applied to groundwaters historically contaminated by CAHs. The procedure was developed using a closed-system, as required by testing VOCs. Since a major point when using exposure systems without gas exchange is linked to the carbon dioxide limitation, we selected to supply CO2 as bicarbonate enrichment. Closed-flasks completely filled with bicarbonate-added test solutions were stoppered with parafilm lids, and connected to a magnetic stirrer mechanism to guarantee the homogeneous suspension of the growing algal cells during the 72 hour-exposure. The increased efficiency of the closed versus the standard procedure was evaluated by the simultaneous use of both methods to test standard chemicals as well as contaminated groundwater samples. Finally, the ability of the closed-system to detect the detoxification effect of the groundwater dechlorination treatment was evaluated by testing pre and post-treatment samples from a laboratory-scale bioelectrochemical reactor. Based on the obtained results, revealing the important advantage of the closed versus the standard system, the proposed ecotoxicological technique proved appropriate for testing groundwater priority contaminants. The combination of its characteristics of simplicity and sensitivity makes it suitable to be routinely used for groundwater monitoring, successfully improving bioremediation studies. Particularly, based on its characteristics, such a sensitive and simple test design could be suitable for checking innovative groundwater bioremediation technologies.