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Assessment of genotoxicity using the micronucleus assay for demonstration of chromo-) ( some aberrations and the frequency of double nuclei in cells and cytotoxicity here changes in ) quantitative characteristics of nucleoli were measured as a parameter of cell metabolism for different organic and inorganic toxic substances was conducted with three organisms, namely, Allium cepa, Lactuca sativa,and Hydra attenuata. Comparative analyses and discussion of data along with results obtained on toxicity and mutagenicity were also performed. Besides correlation between some results, discrepancies were observed as well. For instance, the organic compound lindane had a weak toxicity, but the highest indices of genotoxicity, whereas the very toxic mercury was one of the least in terms of genotoxicity. The noted difference in values of toxicity, mutagenicity, genotoxicity, and cytotoxicity indicates the importance of using an integrated approach to toxicity testing which combines several methods to obtain a more objective and realistic estimation of a chemical toxicity. With this purpose, the trio of methods including the Muta-ChromoPlate test as a modified version of the standard Ames Fluctuation assay, the micronucleus assay, and the nucleolar biomarker are thus proposed for the routine monitoring of chemical toxicity. ᮊ

The cytotoxicity of three substances (mercury(II), metolachlor, and 4-nitroquinoline-N-oxide) was assessed with a set of nucleolar parameters: the average number of nucleoli, the average volume of a single nucleolus, and the proportion of cells with heteromorphic-paired nucleoli (PNhet). Their toxic impact was studied on cells of animal and plant test organisms: onion (Allium cepa), lettuce (Lactuca sativa), and hydra (Hydra attenuata). In general, at concentrations near IC/LC(50) the three chemicals produced similar cytogenetic effects after 30-360 min of contact. For instance, in plant cells (Allium cepa and Lactuca sativa) the toxicants increased the percentage of cells with PNhet, decreased the volume of single nucleoli, and exerted no significant impact on the nucleolar number. In animal cells (Hydra attenuata), they reduced the size of nucleoli, produced no effect on the number of nucleoli, but decreased the share of cells with PNhet. Also, the chemicals affected the cells of the three test organisms to different degrees. Thus, the effectiveness of our approach of using nucleolar biomarker (use of the proposed set of parameters and time schedule of several determinations in the first hours of toxicant contact, etc.) as a means of assessing cytotoxicity was confirmed.