EFFECT OF ZEOLITE ON TOXICITY OF AMMONIA IN FRESH-WATER SEDIMENTS - IMPLICATIONS FOR TOXICITY IDENTIFICATION EVALUATION PROCEDURES

Techniques for reducing ammonia toxicity in freshwater sediments were investigated as part of a project to develop toxicity identification a nd evaluation (TIE) procedures for whole sediments. Although ammonia i s a natural constituent of freshwater sediments, pollution can lead to ammonia concentrations that are toxic to benthic invertebrates, and a mmonia can also contribute to the toxicity of sediments that contain m ore persistent contaminants. We investigated the use of amendments of a natural zeolite mineral, clinoptilolite, to reduce concentrations of ammonia in sediment pore water. Zeolites have been widely used for re moval of ammonia in water treatment and in aqueous TIE procedures. The addition of granulated zeolite to ammonia-spiked sediments reduced po re-water ammonia concentrations and reduced ammonia toxicity to invert ebrates. Amendments of 20% zeolite (v/v) reduced ammonia concentration s in pore water by greater than or equal to 70% in spiked sediments wi th ammonia concentrations typical of contaminated freshwater sediments . Zeolite amendments reduced toxicity of ammonia-spiked sediments to t hree taxa of benthic invertebrates (Hyalella azteca, Lumbriculus varie gatus, and Chironomus tentans), despite their widely differing sensiti vity to ammonia toxicity. In contrast, zeolite amendments did not redu ce acute toxicity of sediments containing high concentrations of cadmi um or copper or reduce concentrations of these metals in pore waters. These studies suggest that zeolite amendments, used in conjunction wit h toxicity tests with sensitive taxa such as H. azteca, may be an effe ctive technique for selective reduction of ammonia toxicity in freshwa ter sediments.