A standardized batch test procedure was developed and used to evaluate the reactivity of twelve newly designed microscale zerovalent iron (mZVI) particles and two biogenic iron sulfides towards a mixture of chlorinated aliphatic hydrocarbons (CAHs) and their breakdown products. For comparison, commercially available mZVIs, nanoscale zerovalent irons (nZVIs), iron sulfides (FeS) and granular zerovalent iron were also tested. Reactivity of the particles was based on observed (k(obs)) and mass normalized (k(M)) pseudo-first-order degradation rate constants, as well as specific surface area normalized reaction rate constants (k(SA)). Sorption characteristics of the particles were based on mass balance data. Among the new mZVIs, significant differences in reactivity were observed and the most reactive particles were identified. Based on k(M) data, nZVI degraded the examined contaminants one to two orders of magnitude faster than the mZVIs. k(M) values for biogenic iron sulfides were similar to the least reactive mZVIs. On the other hand, comparison of k(SA) data revealed that the reactivity of some newly designed mZVIs was similar to highly reactive nZVIs, and even up to one order of magnitude higher. k(SA) values for biogenic iron sulfides were one to two orders of magnitude lower than those reported for reactive mZVIs. (c) 2013 Elsevier B.V. All rights reserved.