ABSTRACT:The potential cytotoxicity and genotoxicity of three industrial wastewaters (brewery, rubber and bottling) in Benin metropolis using the Allium cepa test were investigated. A series of five small onion bulbs were cultivated in 0.01, 0.1, 1, and 10% of the wastewaters (v/v) and after 48 hours, one root tip from each bulb was harvested and processed for cytological studies by the aceto-orcein squash technique. At 72h, their cytotoxic effects on the root tips showed strong growth retardation in high concentrations of all the wastewaters. Compared to the control, treatment with the wastewaters resulted in root growth inhibition with EC50 values of 35, 50 and 62% for bottling, rubber and brewery effluents respectively, and decrease in mitotic index with increasing concentration for all samples and these were statistically significant (p<0.05). Chromosomal aberrations induced in the onion root tip cells were mostly sticky chromosomes and bridges. Chromosomes with disturbed spindles and fragments were also present in appreciable amounts. Based on the EC50 values, the bottling wastewater was most toxic, followed by rubber effluent while effluents from the brewery were least toxic. The findings in this study indicate that there are toxic chemicals present in the wastewaters which are responsible for the observed genotoxic effects on the onion root tip cells. The study also reveals that the Allium test is a useful and reliable tool for the genotoxicity screening of industrial effluents which could be employed by environmental managers before these effluents are finally discharged into the environment. @JASEM