The acute toxicity of nickel to freshwater ciliates.

The acute toxicity of nickel to 12 species of freshwater ciliates was examined in laboratory tests. After exposing standard cultures of the ciliates to a soluble compound of nickel (NiCl(2).6H(2)O) at several selected concentrations close to the lethal limit for 24 h, the mortality rate was registered and the LC(50) values (with 95% confidence intervals) were calculated. Large differences appeared in sensitivities of the 12 species to the metal. Ciliated protozoa such as Spirostomum teres (0.17 mg Ni l(-1), 24-h LC(50)) and Paramecium bursaria (0.36 mg Ni l(-1), 24-h LC(50)) showed the highest sensitivity to the nickel, while Euplotes patella (7.7 mg Ni l(-1), 24-h LC(50)) was the most tolerant species. A comparison of these results with data obtained for other heavy metals indicates that S. teres is an excellent and convenient bioindicator for evaluating the toxicity of waters polluted by heavy metals.