In the toxicity review of the effects of heavy metals to aquatic
organisms it results that the order of toxicity of metals was
generally: CuOCdONiOPbOCr for ciliates (Madoni et al.,
1992, 1994; Madoni, 2000), and CdOCuOCrONiOPb for
invertebrates (McLusky et al., 1986).