A novel toxicity detection methodology based on sulfur-oxidizing bacteria (SOB) has been developed for the rapid and reliable detection of toxic chemicals in water. The methodology exploits the ability of SOB to oxidize sulfur particles in the presence of oxygen to produce sulfuric acid according to the following equation: S + H2O + 1.5O2 → SO 42- + 2H+, ΔG°′ = -587.1 kJ/reaction. The reaction results in an increase in electrical conductivity (EC) and a decrease in pH as SOB convert insoluble sulfur particles to sulfate and protons. The proposed technique is validated using EC and pH data. Using a synthetic stream water (EC = 0.12 mS/cm and pH 7.2), the baseline steady-state EC and pH values were ∼1.0 mS/cm and ∼2.5 over 30 days of testing when hexavalent chromium (Cr6+) was not added to the system. When Cr 6+ was added to the system, the effluent EC decreased and the pH increased due to inhibition of SOB. We found that the system can detect Cr 6+ at a concentration of 5 ppb which is lower than any method to date.
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