The mineralization and biodegradability increase and their combination of two traditional and two relatively new organic contaminants by Fenton reagents with three different types of iron, Fe2+, Fe3+, and Fe-0 were investigated. The traditional contaminants examined were trichloroethene (TCE) and 2,4-dichlorophenol (2,4-DCP) while 1,4-dioxane (1,4-D) and 1,2,3-trichloropropane (TCP) were studied for the relatively new contaminants. The mineralization and biodegradability were represented by dissolved organic carbon (DOC) reduction and the ratio of biodegradable dissolved organic carbon and DOC, respectively. For all four contaminants, Fenton reagent using Fe2+ was more effective in the DOC reduction than Fenton reagents using Fe3+ and Fe-0 in most cases. The types of Fe that provided maximum biodegradability increase were not the same for all four compounds, Fe3+ for TCE, Fe-0 for 2,4-DCP, Fe2+ for 1,4-D, and Fe3+ for TCP. When the combination of DOC elimination and biodegradability increase (least refractory fraction) was considered, Fe2+ was the best choice except for 2,4-DCP which was susceptible to Fe-0 catalyzed Fenton reagent the most. The least refractory fractions remaining after 120 min of reaction were 20-25% for TCE, 2,4-DCP, and TCP and 30-40% for 1,4-D. The iron type in Fenton reaction also affected the type of mineralization kinetics of TCE, 2,4-DCP, and TCP as well as the types of degradation by-products of these contaminants. Some of the by-products found, such as isopropanol and propionic aldehyde, which were produced from Fe-0 catalyzed Fenton degradation of TCP, have not been previously reported. (C) 2008 Elsevier B.V. All rights reserved.