Genotoxic effects of bilge water on mitotic activity in Allium cepa L.

Abstract

Bilge water from oceanic vessels is usually discharged through the bilge wells into the Nigerian marine environment indiscriminately as there is no strong indication of compliance with International Maritime Organization (IMO) regulations relating to its exchange and treatment. In this study, the genotoxic effect of bilge water on root meristems of Allium cepa L. was investigated. Exposure of the onion roots to the wastewater at 1, 5, 10, 25 and 50% (v/v; wastewater/tap water) showed strong concentration-dependent root growth inhibition with an EC₅₀ value of 52.6% at 72 h and induced a variety of chromatid and chromosome structural aberrations at 6, 12, 24 and 48 h. The bilge water was effective in the disturbance of the spindle fibre apparatus at all the concentrations used and this was probably due to the heavy metals (Cu, Mn, Pb, Fe, Cd, Cr, Ag, Ni and Zn) present in the wastewater. In comparison with tap water (negative control), the bilge water was also mitodepressive, causing lower mitotic indices. The findings in this study indicate that the toxic chemicals present in the bilge water are responsible for the observed genotoxic effects, which may contribute to the toxicological assessment of the risk associated with its indiscriminate discharge into the environment.

Keywords:

• Allium cepa
• chromosome aberration
• mitotic index
• bilge water
• root growth

Acknowledgements

The authors are grateful to Mrs Esther Duru for assistance with procurement of bilge water samples. We also acknowledge the contributions of Mr Emmanuel Oseke and Mr Romeo Ofomata for their technical assistance with physico-chemical analyses and the plant bioassay respectively.

Disclosure statement

No potential conflict of interest was reported by the authors.