Sensitivity of Four Test Organisms (Chironomus xanthus, Daphnia magna, Hydra attenuata and Pseudokirchneriella subcapitata) to NaCl: an Alternative Reference Toxicant
In order to establish a safer reference toxicant for use in monthly sensitivity tests at the Ecotoxicology Laboratory (CENA-USP, Brazil), sodium chloride (NaCl p.a.) was evaluated as a possible surrogate for metals during a period of two years with the following test organisms: Chironomus xanthus, Daphnia magna, Hydra attenuata and Pseudokirchneriella subcapitata. All tests were performed following protocols most commonly used for each species. Mean endpoint values obtained were: LC50(96 h) = 5.84 g L–1 (426.9 μS cm–1) for C. xanthus, LC50(48 h) = 5.55 g L–1 (461.5 μS cm–1) for D. magna, LC50(96 h) = 2.57 g L–1 (245.6 μS cm–1) and EC50(96 h) = 1.44 g L–1 (147.2 μS cm–1) for H. attenuata, and IC50(72 h) = 0.87 g L–1 (85.3 μS cm–1) for P. subcapitata. Results indicate good reproducibility, as acceptable coefficients of variation were obtained: 17.03%, 15.02%, 14.84%, 15.28%, and 20.08%, respectively. These results agree with those obtained by other authors, for the same test organisms, using metals such as potassium dichromate. Based on these data, it was possible to conclude that sodium chloride constitutes an adequate alternative reference toxicant to metals, for routine sensitivity tests.