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

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.