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The acute and chronic toxicity of cadmium and zinc to two hydra species

The potential of two hydra species, Hydra vulgaris (pink) and Hydra viridissima (green), for use as invertebrate models for toxicity testing of waterborne metals was investigated. The acute and subchronic toxicities of cadmium (a nonessential metal) and zinc (an essential metal) were determined. Results showed that both the hydra species were more sensitive to cadmium than to zinc, and that green hydra were more sensitive than pink hydra. The mean (SE) 96 h LC50 values of cadmium and zinc for pink hydra were 83 (8.5) and 2300 (150) μg/L, respectively. For green hydra, the respective 96 h LC50 values for cadmium and zinc were 3.0 (0.0) and 935 (46.5) μg/L. The respective 7‐day no‐observed‐effect‐concentrations (NOEC) and lowest‐observed‐effect‐concentrations (LOEC) for pink hydra were <13 and 13 μg/L for cadmium, and <250 and 250 μg/L for zinc. The respective 7‐day NOEC and LOEC values for green hydra were 0.4 and 0.8, μg/L for cadmium, and 38 and 75 μg/L for zinc. Neither 1, 2, or 3 × 90‐min pulse‐exposures to 0.4, 0.8, or 1.5 μg/L of cadmium had any significant deleterious effect on total green hydra numbers after seven days in clean water. Green hydra appeared to be excellent freshwater invertebrate models for testing dissolved metals based on their sensitivity and the ability to rapidly assess population reproduction in the laboratory. © 2001 John Wiley & Sons, Inc. Environ Toxicol 16: 557–565, 2001