Pesticide decomposition through photocatalysis

Findings of the study showed that TiO2 [titanium oxide] and exposure to ultraviolet (UV) light enhanced the photodecomposition of pesticides, namely endosulfan and niclosamide, which are organo-chlorine compounds. The rate of decomposition with TiO2 was directly related to the concentration of the pesticide and the length of time of exposure to UV light. The decomposition rate decreases with higher concentration of the pesticide, as there were more molecules of the pesticide competing in the adsorption of free radicals of TiO2. The longer time of exposure to UV light gave a faster decomposition rate. Decomposition was further enhanced by the presence of H2O2. Treatments with 0.005 M H2O2 gave an even faster decomposition rate (average of 0.14 ppm/hour) than the treatments without H2O2 (average of 0.15 ppm/hour). However, decomposition in the presence of H2O2 favored the production of endosulfan sulfate, the intermediate product resulting from the oxidation of the -SO3 group of the endosulfan. With H2O2 endosulfan sulfate was 41.18 percent while the chloride ions constituted 3.76 percent in the golden snail tissues. Without H2O2, a reversal in the levels of the products was observed, i.e., the chloride ions were higher (33 percent) than the endosulfan sulfate (1.60 percent). Bioaccumulation in living organisms of the intermediate decomposition products could be fatal and biomagnified. The study on bioaccumulation of endosulfan sulfate and chloride ions in the golden snail tissues showed that these photocatalitically degraded products may recombine resulting in the reformation of the pesticide within the bodies of the snail. Therefore, snails that have bioaccumulated endosulfan sulfate and chloride ions are not safe to eat. The presence of TiO2 in the soil generally enhanced the release of some macro- and micro- nutrients to the rice crop, which helped improve the grain yield. In the pot and field experiments on flooded soils planted to rice, the data showed that T1O2 in the presence of light decreased the total N, NH4-N, P, Cu and Zn content of the soil, possibly due to fixation by TiO2. On the other hand, the concentration of K, Ca, Fe and Mn increased. A positive interaction was obtained from the organic-inorganic fertilizer combination with TiO2, as reflected in a higher grain yield of 7.20 t/ha. TiO2 with inorganic fertilizer alone showed no enhancing effect on grain yield, which was 4.56 t/ha. In terms of the growth of microorganisms, the preliminary study revealed that T1O2 helped promote the rapid multiplication of aerobic soil microflora due to the ability of TiO2 to adsorb oxygen gas