In the present study, the fate of trivalent chromium (Cr(III)) during ozonation of ultrapurified water and wastewater effluent was investigated. In experiments conducted in phosphate buffered ultrapurified water, O₃ alone in excess was inefficient to oxidize Cr(III) (only about 10–15% of total Cr(III) content), while in presence of the secondary oxidant, OH radical, almost all Cr(III) was oxidized to hexavalent chromium (Cr(VI)). In a wastewater effluent, spiked with Cr(III), only about 10–20% of Cr(III) was oxidized with specific ozone doses in the range 0.15–1.5 gO₃/gDOC, although O₃ and OH radical were both available for reaction. Cr(VI) formation was monitored in parallel with the abatement of some common micropollutants, reacting with differing apparent second-order rate constants with ozone, decreasing in the order carbamazepine>> benzotriazole> atrazine> p-chlorobenzoic acid (pCBA). Carbamazepine and benzotriazole were abated to >80% for specific O₃ doses of 0.3 gO₃/gDOC and 0.8 gO₃/gDOC, respectively. The more ozone-resistant compounds (atrazine and pCBA) required a specific ozone dose of about 1.25 gO₃/gDOC for the same relative abatement. At this specific ozone dose (i.e., 1.25 gO₃/gDOC), only about 20% of Cr(III) was oxidized to Cr(VI), whereas only 10% of Cr(III) was oxidized to Cr(VI) at a more realistic specific ozone dose for enhanced wastewater treatment for micropollutant abatement (0.5 gO₃/gDOC). Therefore, for typical Cr(III) levels in municipal wastewaters, effluent ozonation only leads to toxicologically insignificant Cr(VI) concentrations.