Abstract
The aim of this study was to evaluate the cytotoxicity and genotoxicity of treated wastewater that is discharged in the downstream Alhamed valley, in Almadinah Almonawrah city, Saudi Arabia. Treated wastewater samples were collected from the outlet of sewage treatment plant (STP) and three downstream locations, approximately (10, 20, and 30 km) of the plant. The cytotoxicity and genotoxicity of the samples were assessed using Allium cepa mitotic index (MI) and chromosome aberrations (CA) assays respectively. Onion bulbs were exposed to different concentrations (100, 50, 25, and 12.5%) of treated wastewater for 12 hours. Bulbs exposed to tap water were used as negative controls. Chromosome aberrations (CA) were induced by treated wastewater in a dose dependent manner. In addition, CA were significantly higher at the outlet of STP than the downstream locations. Moreover, the frequency of CA decreased as the distance from STP increased. With respect to cytotoxicity, treated wastewater from all locations induced significant decreases in MI and significant increases in the frequency of aberrant cells except the 30 km sampling point (concentration 12.5%). In conclusion, treated wastewater seems to possess genotoxic and cytotoxic compounds that get eliminated by movement of the water away from STP.