Example Number of identify metaphase cell Average metaphase cells with chromosome damage Average level genotoxicity (%) Average length of root (mm) Percentage (%) length root of negative control Wastewater; influent in CW 200 58 ± 6.0 29.0* ± 3.0 17 ± 3.5 41.4 Cleaning water effluent out CW 200 7 ± 2.0 3.5* ± 1.0 42 ± 3.5 100.2 Negative control-NC (tap water filtered with R.O.-reverse osmosis 200 6 ± 2.0 3.0 ± 1.0 41 ± 2.0 100.0 Positive control-PC (10 ppm Methan Methilsulphonate–MMS 4016 Sigma) 200 61 ± 5.0 31.0 ± 2.5 12 ± 3.0 29.2

Table 1: The average length of the roots and cytological effects of investigated samples and both controls of the test plants of Allium cepa L. Cytological effects– investigation of genotoxicity level and Average root length of test plant Allium cepa L.–investigation of general toxicity. From each of 5 bulbs in a series of 5, one root tip is taken for each of 5 slides. From each slide, 200 metaphase cells are scored. The degree of general toxicity of the analysed samples (5 bulbs per sample) was assessment from the mean root lengths expressed as a percentage of the mean root length of the negative control.