Bioremediation and toxicity bioluminescent assay of contaminated soils

Three different strains of bioluminescent bacteria (Vibrio sp.) have been applied to the analysis of samples of slime from Marano lagoon (Venice, Italy) and of soil from oil terminals (Ben Jabbar, Libya), with the aim to assess their biotoxicity and to evaluate the effects of bioremediation treatments carried out with hydrocarbons degrading bacteria. Many researchers have studied the development of rapid and sensitive bioassays to monitor and assess the discharge of toxic materials. Accordingly, toxicity tests based on bioluminescent micro-organisms have been used because of their sensitivity [1]. Bioluminescent bacteria (BLB), present in marine, freshwater and terrestrial environments, emit light when they find themselves in an optimal environment. Therefore, in vivo luminescence is a sensitive indicator of xenobiotic toxicity to micro-organisms because it reflects the metabolic status of the cell. A decrease in luminescence can be measured when noxious substances are present in the medium. The soil in industrial areas, the slime from sea costs or lagoons, the sludges from wastewater treatment plants are contaminated by a large variety of toxic pollutants, such as hydrocarbons, organic substances and heavy metals. Concerning these kinds of pollutants exist regulatory rules that define the acceptable levels and impose suitable treatments of highly polluted materials to reach these levels. In this study the three marine Vibro logei strains showed, among them, different sensitivity to the different pollutants contained in the samples: heavy metals in the lagoon samples and hydrocarbons of various chain length in soil samples. The measurements of emitted light, carried out in medium containing 3% NaCl, were done after short time of contact (60 minutes) and at long time intervals (16 hours) and the results expressed as percentage inhibition with respect to the blank emission (100%). The trend of acute and chronic toxicity was similar for each strain. By analysing with BLB the hydrocarbons contaminated samples before and after various period of bioremediation treatment it was possible to observe an increasing toxicity of the treated samples. Thus, the BLB could represent a useful biomonitoring tool to evaluate the changes occurring during remediation processes, even in case of on-field conditions, like for treatments carried out on boats. [1] Girotti S, Bolelli L, Roda A, Gentilomi G, Musiani M. (2002). Improved detection of toxic chemicals using bioluminescent bacteria. Anal. Chim Acta 471, 113-120.