Ecotoxicological tests performed in waters with low salinities, typical of estuarine environments, are limited regarding the availability of test organisms. The amphipod Hyalella azteca, an organism protocoled for trials with freshwater sediments, presents a potential for use in saltwater tests in which the confounding factors, such as salinity and sediment grain size, should be evaluated to avoid errors in the results in relation to the sensitivity of the organism. Thus, amphipod cultivations in salinities of 0, 5, 10 and 20 were conducted, to perform tests of tolerance to salinity, and sensitivity to a reference toxicant. The tolerance of the species to different sediment grain sizes and organic matter contents was evaluated in tests with reconstituted sediments in five different compositions, varying the content of organic matter (5 to 20%), clay and sand (0 to 95%). The results of the cultivations showed that animals maintained present the best reproduction and survival rates at salinity 5, and a tolerance limit under chronic conditions, at salinity above 10. The salinity can be considered a confounding factor since the tests carried out with the reference toxicant showed the higher resistance of the species under conditions of higher salinities. The species present tolerance to different sediment grain sizes and organic matter contents; therefore, this factor does not interfere in the survival of H. azteca during the ecotoxicological tests.