We report the irradiation of titanium dioxide suspensions (Hombikat UV100 and P25) under different conditions regarding the source of dissolved organic carbon (2,4-dihydroxybenzoic acid and brown water from a bog lake), and with and without added copper(II) ions. In contrast to P25 suspensions, we found no significant bromoform formation in Hombikat UV100 suspensions, likely because bromoform is degraded faster with Hombikat UV100 than with P25, preventing accumulation. In the case of P25 suspensions, the presence of 10 mu M of added Cu(2+) significantly inhibited bromoform formation. Bromoform was the only measurable trihalomethane (THM), even in the presence of 250 mg L(-1) chloride ions. The concentrations of formed THM were below the limits for drinking water under all investigated experimental conditions. (C) 2010 Elsevier B.V. All rights reserved.