Acute toxicity of lead, chromium, and other heavy metals to ciliates from activated sludge plants.

Numerous papers have been published which deal with the occurrence of heavy metals in the various components of freshwater ecosystems (Radwan et al. 1990; Scanferlato and Cairns 1990; Hintelmann et al. 1993) and sewage treatment systems (Yetis and Gokcay 1989; Cimino and Caristi 1990; Dilek and Yetis 1992; Melcer et al. 1992; Moriyama et al. 1992). However, only a few papers refer to the presence and effect of heavy metals in populations of aquatic ciliated protozoa (Parker 1979; Cairns et al. 1980; Fernandez-Leborans et al. 1985). In particular, little information exists concerning the lethal concentrations (LC50) of heavy metals in ciliate populations that colonize the activated sludge or the biofilm of waste treatment plants.