Effect of soluble sulfide on the activity of luminescent bacteria

Sulfide is an important water pollutant widely found in industrial waste water that has attracted much attention. S2?, as a weak acidic anion, is easy hydrolyzed to HS? and H?S in aqueous solution. In this study, biological tests were performed to establish the toxicity of sulfide solutions on luminescent bacteria. Considering the sulfide solution was contained three substances--S2?, HS? and H?S--the toxicity test was performed at different pH values to investigate which form of sulfide increased light emission and which reduced light emission. It was shown that the EC?? values were close at pH 7.4, 8.0 and 9.0 which were higher than pH 5 and 10. The light emission and sulfide concentrations displayed an inverse exponential dose-response relationship within a certain concentration range at pH 5, 6.5 and 10. The same phenomenon occurred for the high concentration of sulfide at pH 7.4, 8 and 9, in which the concentration of sulfide was HS? > H?S > S2?. An opposite hormesis-effect appeared at the low concentrations of sulfide.