Abstract: Iron composite particles for purifying soil or ground water, comprise an iron component, at least one noble metal selected from the group consisting of ruthenium, rhodium and palladium, and carbon or aluminum, and having a noble metal content of 0.01 to 5.00% by weight and a particle diameter of 0.01 to 1.0 ?m. The iron composite particles and the purifying agent according to the present invention are capable of decomposing aliphatic organohalogen compounds such as dichloromethane, carbon tetrachloride, 1,2-dichloroethane, 1,1-dichloroethylene, cis-1,2-dichloroethylene, 1,1,1-trichloroethane, 1,1,2-trichloroethane, trichloroethylene, tetrachloroethylene, 1,3-dichloropropene or the like, and aromatic organohalogen compounds such as dioxins, PCB (polychlorinated biphenyl) or the like, which are contained in soil, ground water or waste water, at ordinary temperature in an efficient and economical manner.

Abstract: Acicular magnetic iron oxide particles comprise:acicular magnetite particles having 10 to 24% by weight of ferrous as core particles;a magnetite coating which is formed on the surfaces of said acicular magnetite particles by epitaxial growth and which has maghemite at least in a part of the surface of said magnetite coating; anda cobalt-containing oxide layer which is formed on said magnetite coating and which contains cobalt of 1.5 to 2.5 wt % based on the total weight of said acicular magnetic iron oxide particles.