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An aquatic model ecosystem for use in assessing biological effects of polutants and their chemical fate was developed. The basic test units were housed in 3-litre battery jars and used sand as the substrate and modified algal assay medium as the aqueous component. The biological components included a benthic oligochaete, Lumbriculus variegatus; a zooplankter, Daphnia magna; and the alga Selenastrum capricornutum. A small air pump in the center of each jar was maintained at a low bubbling rate to keep the algae in suspension. Two chemicals, 2,4,6-trinitrotoluene (TNT) and 2,4-dinitrotoluene (DNT), were tested separately using a 21-day exposure period. Each chemical was tested in duplicate, and agreement between the replicates was good. The direct toxic effects of the test chemicals were clear-cut, as were the secondary effects, such as reduced reproduction of daphnids at concentrations that reduced the algal population. The rate of loss of the chemicals from the water column was in proportion to the concentration of the chemicals and was reduced in jars that had been autoclaved and contained no biota.
model ecosystem, microcosm, aquatic toxicology, chemical fate, 2,4-dinitrotoluene, 2,4,6-trinitrotoluene, Daphnia magna, Lumbriculus variegatus, Selenastrum capricornutum, hazard assessment
Director, Aquatic Toxicology Program, SRI International, Menlo Park, Calif.