Compositions in accordance with the principles of the present invention comprise a compressed mixture of fibrous organic materials and multi-valent metals used to remove organic chemical contaminants. The compositions are made into a pre-shaped, compressed form used to form a permeable reactive barrier for decontamination of soils, sediments, sludges, and waters containing environmental pollutants. The compressed mixture, comprising the fibrous organic particles and one or more multivalent metallic particles, is formed into reactive pellets, granules, and other pre-shaped structures for use in constructing a reactive barrier, typically for use in a contaminated environment or in an industrial process. By way of example, the pre-shaped structure may be used to construct a reactive barrier to remove halogenated organic chemical contaminants, nitroaromatic organic contaminants, or certain inorganic contaminants from various terrestrial and aquatic based ecosystems.