TOLERANCE OF THE NEMATODE CAENORHABDITIS-ELEGANS TO PH, SALINITY, ANDHARDNESS IN AQUATIC MEDIA

The toxicity of many chemicals depends on the physical conditions of t he test environment, and any change or adjustment made to the tests ca n alter the results. Therefore it is important to establish the sensit ivity of the test organism over a range of test conditions to determin e when it is necessary to make adjustment and to what extent. In this study, we established the tolerance range of the nematode Caenorhabdit is elegans for pH, salinity and hardness using 24- (without food sourc e) and 96-h (with food source) aquatic toxicity tests. The tests were performed in two media: K-medium and moderately hard reconstituted wat er (MHRW). C. elegans has high tolerance under these test conditions. In K-medium worms survived a pH range of 3.1 to 11.9 for 24 h and 3.2 to 11.8 for 96 h without significant (p > 0.05) lethality. In MHRW the pH range was 3.4 to 11.9 for 24 h and 3.4 to 11.7 for 96 h. Salinity tolerance tests were approximated with NaCl and KCl individually. Up t o 15.46 g/L NaCl and 11.51 g/L KCl were tolerated by C. elegans in K-m edium without significant lethality (p > 0.05). In MHRW higher salt co ncentrations were tolerated; about 20.5 g/L NaCl and 18.85 g/L KCl did not show any adverse effect compared to control. Hardness tolerance w as tested by adding NaHCO3. The nematode could tolerate 0.236 to 0.246 g/L of NaHCO3. The high tolerance of C. elegans to these test conditi ons (pH, salinity, and hardness) allows more versatility than other or ganisms commonly used in aquatic toxicity tests. It also allows the mo nitoring of effluents and receiving waters from freshwater or estuarin e sources without dilution or adjustment.