Acute toxicity of metals and reference toxicants to a freshwater ostracod, Cypris subglobosa Sowerby, 1840 and correlation to EC50 values of other test models

The ostracod Cypris subglobosa Sowerby, 1840 static bioassay test on the basis of a 48 h of 50% of immobilization (EC50) has been used to measure the toxicity of 36 metals and metalloids and 12 reference toxicants. Among the 36 metals and metalloids, osmium (Os) was found to be the most toxic in the test while boron (B), the least toxic. The EC50 values of this study revealed positive linear relationship with the established test models of cladoceran (Daphnia magna), sludge worm (Tubifex tubifex), chironomid larvae (Chironomus tentans), protozoan (Tetrahymena pyriformis), fathead minnow (Pimephales promelas), bluegill sunfish (Lepomis macrochirus), and aquatic macrophyte duckweed (Lemna minor). Correlation coefficients (r2) for 17 physicochemical properties of metals or metal ions and EC50s (as pM) were examined by linear regression analysis. The electronegativity, ionization potential, melting point, solubility product of metal sulfides (pKsp), softness parameter and some other physicochemical characteristics were significantly correlated with EC50s of metals to C. subglobosa. The reproducibility of toxicity test was determined using 12 reference toxicants. The coefficient of variability of the EC50s ranged from 6.95% to 55.37% and variability was comparable to that noticed for D. magna and other aquatic test models. The study demonstrated the need to include crustacean ostracods in a battery of biotests to detect the presence of hazardous chemicals in soils, sewage sludges, sediments and aquatic systems.