Medicinal leech (Hirudo verbana) were exposed for 30 days to various concentrations of Zn (0.188, 0.375, 0.75, 1.5, 3.0, 6.0, 12.0, 24.0 and 48.0 mg/l), Cu (0.004, 0.008, 0.016, 0.032, 0.063, 0.125, 0.25, 0.5, and 1.0 mg/l) and their equitoxic mixture Zn + Cu (0.188 + 0.006, 0.375 + 0.012, 0.75 + 0.023, 1.5 + 0.045, 3.0 + 0.09, 6.0 + 0.18, 12.0 + 0.36, and 24.0 + 0.72 mg/l). The LC₅₀ values were determined for the following exposures: 48 h, 96 h, 10 d, 20 d, and 30 d. Mortality of animals was observed during the whole 30-d period. Lethal eff ects of metals on leech were prolonged as compared to fish; therefore, long-term experiments for leech are needed. The sensitivity of leech to Cu was remarkably higher than to Zn. A partially additive interaction of Zn and Cu in the mixture was found. The additive eff ects were considerably higher during the shorter (96 h, 10 days) than during the longer exposures (20 and 30 days).

Keywords: copper, medicinal leech, heavy metal mixture, long-term exposure, zinc