Genotoxicity Screening of Industrial Effluents using Onion bulbs (Allium cepa L.)

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 Industries are undoubtedly indispensable components of a nation’s development; however, the impact of industrial wastewaters on aquatic and terrestrial ecosystems has drawn a lot of attention worldwide because of its overwhelming environmental significance. Industrial wastewater originates from the wet nature of most large industries which require large quantities of water for processing and disposal of wastes. Most industries are therefore, located near water sources. Industrial wastewater is not only concentrated but plentiful, so the pollution potential of industrial wastewater is by far greater than that of domestic wastewater. In Nigeria, over 80% of the industries discharge solid wastes, liquid effluents and gaseous emissions directly into the environment without any treatment (Federal Ministry of Water Resources, 1994). Despite existing legislations, of the 200 randomly assessed industries, only 18% perform rudimentary recycling prior to disposal of the wastes (FEPA, 1998). Several higher plant systems, including bioassays with plant roots have provided cheaper, easier, sensitive, useful, reliable and valuable alternative methods for the determination of the adverse effects of environmental pollutants to the usual assays carried out on experimental animals (Grant, 1978). Most of the studies indicate that there is an excellent correlation between chromosome abnormalities and mutagenic activity found in root-tip systems and those found in mammalian cell systems. Observation of the root tip system of plants therefore constitutes a rapid and sensitive method for environmental monitoring (Majer et al., 2005). Allium cepa L. has been used as a first-tier assay for the detection of environmental chemicals that may pose genetic hazards from a wide range of pollutants such as sewage effluents (Ukaegbu and Odeigah, 2009), leacheates (Bakare and Wale-Adeyemo, 2004, Chandra et al., 2005) and chemicals (Seetharaman et al., 2004). Cytotoxicity and environmental pollution have been assessed by the in vivo onion (Allium cepa) root tip cell test which is known to give similar results to in vitro animal cytotoxicity tests (Vicentini et al., 2001; Teixeira et al., 2003). A. cepa test has also been used by many authors to evaluate cytotoxicity and genotoxicity of industrial effluents (Rank and Nielson, 1998; Chauhan et al., 1999; Grover and Kaur, 1999; El-Shahaby et al., 2003, Babatunde and Bakare, 2006; Junior et al., 2007; Abdel-Migid et al., 2007; Şık et al., 2009; Samuel et al., 2010). In a study conducted on the toxicity of wastewaters from three industrial establishments in Benin City, Nigeria, differential lethality was established on Chironomus travalensis (Diptera larvae) (Olomukoro and Okhumale, 2008). We are not aware of any reports on the genotoxicity of these industrial effluents. This study was therefore undertaken to corroborate or otherwise, the nature and extent of toxicity of the effluents discharged from the same industrial establishments using a higher plant monitoring system, the Allium cepa assay. MATERIALS AND METHODS Three industrial effluents: a brewery (Br), bottling company (Bt) and rubber processing industry (Rr) were collected from their discharged points within the Benin City metropolis situated between latitudes 6 o 06’ N, 6 o 30’ N and longitudes 5 o 30’ E, 5 o 45’ E and an area of about 500 square kilometres. Effluents from these industries are discharged into close-by rivers; the brewery (Br) and rubber processing industry (Rr) effluents are discharged into the Ikpoba