Ecotoxicological approach to evaluate the detoxification effect of a bioelectrochemical dechlorination treatment

While the success of the decontamination treatments is generally controlled by chemical analysis of selected contaminants, the ecotoxicological approach should have a major part within any restoration program where detoxification represents the basic goal of the remediation process. The detoxification effect measured by biological testing can provide the toxicity response which integrates the impacts of complex mixtures of contaminants. Since chemical analysis only detects the selected substances for which it is suitable, causative toxicants of the mixture might be overlooked or accidently ignored, hence the toxicity of environmental samples can be hardly predicted by chemical analysis solely. One of the reasons why ecotoxicological testing is rarely employed is that standard test procedures may be not appropriate for difficult substances like in the case of volatile organic compounds, such as chlorinated aliphatic hydrocarbons (CAHs), which are most common groundwater priority contaminants. An ecotoxicological procedure of algal testing being both appropriate for testing volatile compounds and relatively easy to be performed has been set up in our laboratory. The efficiency of its application to groundwater bioremediation studies has been evaluated. The ecotoxicological procedure we set up using Pseudokirchneriella subcapitata as test organism consists of a head-space free system of closed-flasks completely filled with bicarbonateadded test solutions, connected to a magnetic stirring mechanism preserving the homogeneous suspension of the algal cells. Tests with closed and standard systems were simultaneously performed with the aim to evaluate the increased efficiency of the closed versus the standard procedure. The toxicity of standard chemicals, such as trichloroethene and tetrachloroethane, selected as model compounds of CAH contamination, revealed a very high increase in sensitivity of the closed-system. Similar results of increased sensitivity were also obtained when testing environmental samples, such as CAH contaminated groundwaters, where the same chemicals were mainly involved. Given the sensitivity of the approach, the ecotoxicological procedure was finally applied to detect the effect of the bioremediation process of groundwaters by testing pre and post-treatment samples from a laboratory-scale bioelectrochemical reactor. The procedure revealed its ability to evaluate the detoxification effect of the dechlorination treatment, showing important decrease of the toxicity of the CAH contaminated groundwaters, up to 78% Toxicity Reduction. These results are proving the efficacy of the adopted bioremediation technology and, especially, the ability of the ecotoxicological procedure to control the success of the decontamination process.