Photocatalytic-assisted ozone degradation of metolachlor (MTLC) aqueous solutions was investigated using neat TiO2 (prepared by sol-gel method) and TiO2/carbon composite (prepared from commercial available metal oxide and carbon phase) as catalysts. In terms of MTLC degradation, O-3 on its own is enough to achieve 100% removal, but the introduction of light increased the rate of removal. On the other hand, the combination of O-3 with light and the tested catalysts is mandatory to reach high mineralization in short reaction times. After 60 min of reaction, the TOC removal was 87% and 75% in the presence of the prepared composite and TiO2, respectively. The concentration of two short chain carboxylic acids, oxalic and oxamic acids, was followed during MTLC degradation. The amount of these acids decreased when O-3 and light were combined. In general, nitrogen ions, such as nitrate and ammonium, were detected in the studied processes. All treatments released ammonium and light based processes also produced nitrate. Microtox analysis showed that the combined process in the presence of the prepared catalysts led to a remarkable reduction in the toxicity of the treated solution, decreasing the inhibition of luminescent activity of Vibrio Fisheri from 74% to 12%. (C) 2016 Elsevier B.V. All rights reserved.