N-methyl-P-aminophenol (metol) ozonation in aqueous solution: Kinetics, mechanism and toxicological characterization of ozonized samples

The ozonation of metol, one of the main constituents of photographic develo pers, has been studied in aqueous solution in the pH range 2.0-7.0. Main re action mechanisms have been assessed on the basis of observed reaction inte rmediates and products at varying pH of the solution. The effect of mangane se addition-Mn-II ions or solid MnO2-to the reacting system has also been e valuated. The capability of the ozonation treatment to reduce the toxicity of metol-c ontaining aqueous solutions, with respect to selected organisms, such as al gae, has also been studied according to reported standard procedures. The r esults of toxicological assessments show that high levels of detoxification are achieved after 20 min of ozonation treatment and that longer treatment s cause an increase in the toxicity of the solution due to the formation of secondary reaction products. The adoption of proper chemical and fluid dyn amic submodels enabled the estimation of the reaction kinetics of ozone tha t attack to the substrate. (C) 2000 Elsevier Science Ltd. All rights reserv ed.