The aim of this research was to analyze the effects and the modes of action of elemental sulfur (S(0)) in bioluminescence and respiration of Vibrio fischeri cells and the enzymes crude luciferase, pure catalase, and alcohol dehydrogenase (ADH). Metallic copper removed sulfur and reduced the toxicity of acetone extracts of sediment samples analyzed in the bioluminescence test. The sulfur inhibition of cell bioluminescence was noncompetitive with decanal, the luciferase substrate; reversible, with maximum toxicity after 15 min (EC(50) = 11.8 microg/L); and almost totally recovered after 2 h. In vitro preincubation of crude luciferase extract with sulfur (0.28 ppm) weakly inhibited bioluminescence at 5 min, but at 30 min the inhibition reached 60%. Increasing the concentration of sulfur in the parts per million concentration range in vitro decreased bioluminescence, which was not constant, but depended on exposure time, and no dead-end/total inhibition was observed. The redox state of enzymes in the in vitro system significantly affected inhibition. Hydrogen peroxide restored fully and the reducing agent dithiothreitol, itself toxic, restored only partially luciferase activity in the presence of sulfur. Sulfur (5.5 ppm) slightly inhibited ADH and catalase, and dithiothreitol enhanced sulfur inhibition. High sulfur concentrations (2.2 ppm) inhibited the bioluminescence and enhanced the respiration rate of V. fischeri cells. Elemental sulfur data were interpreted to show that sulfur acted on at least a few V. fischeri cell sites: reversibly modifying luciferase at sites sensitive to/protected by oxidative and reducing agents and by affecting electron transport processes, resulting in enhanced oxygen consumption. Sulfur together with an enzyme reducing agent inhibited the oxidoreductive enzymes ADH and catalase, which have --SH groups, metal ion cofactors, or heme, respectively, in their active centers.

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This diverse review discusses biotest species and results scoring systems, which were applied to aquatic toxicity assessment of effluents/wastewater (WW) and landfill leachate (LL). European and American aquatic toxicity testing is reviewed. An example of Lithuanian research data on LL biotesting with aquatic organisms of different phylogenetic and ontogenetic levels is presented. Acute toxicity WW and LL is assessed on the basis of (L(E)C50, acute Toxic Units (tua), pt values, and, by applying different simple result scoring systems or toxicity thresholds. The differences in legislation and recommendations for biotest application in WW and LL aquatic toxicity testing are compared. It is concluded that WW and LL lowest acute toxicity data (tua value 0.3) should be considered equally as risk to aquatic environment, and technical management decisions should be made. The universal features of toxicity scoring systems, the problems of inventory of old small landfills and cost effective approach are discussed.

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