Toxicity of inorganic compounds in the Spirotox test: a miniaturized version of the Spirostomum ambiguum test.

The Spirostomum ambiguum toxicity test has been intensively studied in the Department of Environmental Health Sciences, Warsaw University of Medicine for the last 5 years. The purpose of the present work was to develop and evaluate a miniaturized microplate version of the test, called the Spirotox test, and to estimate the toxicity of selected inorganic compounds to the Spirostomum ambiguum. The test was carried out in conventional 24-well (6 x 4) polystyrene multiwell plate. Preliminary test was one control and 11 toxicant concentrations with two duplicates. Definitive test was one control and five toxicant concentrations with three duplicates per concentration. Dilution of the sample was made directly in the plate. Toxicity series of heavy metals based on 24-h LC50 may be established as follows: Cu > Ag > Hg > Cr > Cd > Zn > Ni > Pb > Co > Mn. The series may be divided into four classes: extremely toxic: below 0.1 ppm (Cu, Ag, Hg); very toxic: 0.1-1.0 ppm (Cr, Cd, Zn, Ni); toxic: 1.0-10 ppm (Pb, Co); and low toxic: above 10 ppm (Mn). Anions were much less toxic to S. ambiguum than cations. Using the same classification, only cyanide (CN) was toxic, other anions were low toxic. Toxicity series based on 24-h LC50 may be established as follows: CN > SeO3 > Cr2O7 > NO2 > S2O3 >WO4 > BO3.