RESUMEN
Daphnia magna Straus, a common organism used for freshwater sediment toxicity tests, was evaluated to determine its tolerance to salinity and suitability for tests with estuarine water and sediments. Daphnids were exposed for 2 to 21 days to salinity in a variety of water-only tests, in tests with freshwater sediment overlain by salt water, and in tests with estuarine sediments overlain by freshwater. Daphnid age, test length, and temperature seemed to have little effect upon the range of LC50, NOAEL, and LOAEL values. LC50s for all tests ranged from 5.10 to 7.81 g/L, with a mean of 6.6 g/L salinity (measured conductivity 10.0 mS/cm) [corrected]. The mean NOAEL and LOAEL values based on production of young were 4.6 and 6.9 g/L salinity (measured conductivity 7.1 and 10.5 mS/cm) [corrected], respectively. The results indicate that D. magna will survive and reproduce well in water with salinities below 4 g/L and demonstrate the potential usefulness of this organism in monitoring sediment toxicity from both freshwater and estuarine wetland sites.