Oxidation-Reduction Potential of Chlorine Solutions and Their Toxicity toErwinia carotovorasubsp,carotovoraandGeotrichum candidum

Abstract

The toxicity of chlorine solutions to cells of Erwinia carotovora subsp. carotovora and conidia of Geotrichum candidum suspended in water at pH 6.0, 7.0, or 8.0 was correlated with the free chlorine concentration and oxidation-reduction potential of the solutions. The oxidation-reduction potential was directly correlated with the Log 10 of the chlorine concentration at each pH. Cells of E. c. carotovora were 50 times more sensitive to chlorine than were conidia of G, candidum, with populations of 1 × 10 7 cfu/ml and 1 × 10 7 conidia per milliliter, respectively, Populations of E. c, carotovora were reduced below detectable levels (< 10 2 cfu/ml) by approximately 0,5, 0,5, or 0,75 mg of free chlorine per liter at pH 6.0, 7.0, or 8.0, respectively. In contrast, with conidia of G. candidum, 25, 25, and greater than 30 mg/L, respectively, were required to produce a similar level of efficacy. With both organisms, population reductions were associated with higher initial oxidation-reduction potentials at pH 6.0 than at pH 8.0