Assessing Toxicity of Copper, Cadmium and Chromium Levels Relevant to Discharge Limits of Industrial Effluents into Inland Surface Waters Using Common Onion, Allium cepa Bioassay

Toxicity of copper, cadmium and chromium relevant to established tolerance limits for the discharge of industrial effluents into inland surface waters was evaluated by Allium cepa bioassay. The roots of A. cepa bulbs exposed to Cu2+ (3 mg L-1) individually or in mixtures with Cd2+ (0.1 mg L-1) or/and Cr6+ (0.1 mg L-1) exhibited the highest growth inhibition, mitotic index depression and nuclear abnormalities. Root tip cells exposed to Cr6+ or Cd2+ alone or in mixture displayed significant chromosomal aberrations in comparison to the controls. EC50s for root growth inhibition followed the order Cu2+ < Cd2+ < Cr6+ indicating greater toxicity of copper. The results show that the industrial effluent discharge regulatory limits for these metals need to be reviewed considering potential cyto-genotoxicity to biological systems.