The photochemical process of Cu (II) reduction by heterogeneous photocatalysis using titanium dioxide (TiO2) Degussa P-25 and a 254 mn UV-C lamp was studied. The aim of this work was to determine the efficiency of the photocatalytic process to remove 100 pprn of copper (II) ion concentration from a water solution. A statistics-based experimental design with response surface methodology (RSM) was employed to investigate the effect of operating conditions on photocatalytic reduction. The experimental results were evaluated using multivariate analysis with the program MODDE 7.0. The parameters studied were catalyst mass, pH, and reaction time. After optimizing the variables, degradation kinetics were performed to corroborate the model. The regression analysis with R-2 value of 0.98 shows a close fit between the experimental results and the model predictions. The value obtained for the reaction rate constant was 0.0246 min(-1). Three-dimensional response surface plots were used to visualize parameter interactions. The optimum pH (4.3) and titanium dioxide mass (0.5 g) achieved the highest efficiency, reaching 80% of copper (II) ion reduction. Two different bioassays, using Daphnia magna and Pseudomonas aeruginosa, were performed to determine acute toxicity reduction after the treatment. The results obtained show that the bio-toxicity reduction reached 80%. (C) 2009 Elsevier B.V. All rights reserved.