*2.5. Genotoxicity Assessment*

The genotoxicity of both untreated and treated industrial effluents was determined using the *Allium cepa* root chromosomal aberration assay [41–43]. After the removal of primary roots of freshly purchased onion bulbs, bulbs were placed on Couplin jars containing distilled water (negative control) and industrial effluents for 48–72 h for rooting. The Couplin jars were kept in a BOD (Biochemical Oxygen Demand) incubator at 25 ± 2 ◦C until roots grew. Care was taken to fill the coupling jars with exposure media on a daily basis so that the onion bulbs were emersed in solution and the root primordia were under continuous exposure to the treatment. Distilled water was used as a negative control during the study. The onion bulbs after treatment were thoroughly washed. The root tips were plucked with forceps and put in a solution of glacial acetic acid and Ethanol in the ratio of 1:3 (Farmer's fluid). The root tips were squashed in aceto-orcein stain to prepare slides. At least five slides consisting of approximately 500 dividing cells were examined under a light microscope to calculate mitotic index (MI) and to score different types of aberrations for each sample. The chromosomal aberrations were categorized into physiological (outcomes of spindle inhibition) and clastogenic (formed due to damage of DNA) based on the descriptions given earlier [42,44].
