Rate Constants for Herbicide Degradation by Ozone

Rate constants for the degradation of five herbicides (Mecoprop, MCPA, 2,4-D, Simazine and Atrazine) by ozone were determined in the laboratory under controlled conditions at both acidic and neutral pH using a competition kinetic method. The order of herbicide degradation rate was found to be as follows: Mecoprop > MCPA > 2,4-D > Simazine > Atrazine, both at pH 2 and pH 7.5. The half-life times for herbicide removal at pH 7.5 and in the presence of bicarbonate ions are, respectively, 25.9; 27.5; 39.5; 66.6 and 94.2 minutes for Mecoprop, MCPA, 2,4-D, Simazine and Atrazine at a dissolved ozone concentration of 10 μM. The kinetics of ozone consumption for the three phenoxyalkyl acid derivatives were investigated at pH 2. The study has demonstrated that at neutral pH the initial concentration ratio of two herbicides in solution together did not affect their relative degradation rate.