Toxicity evaluation of waste effluent from cassava-processing factory in Lagos state, Nigeria using the Allium cepa assay

Abstract

Mutagenic and genotoxic effects of cassava wastewater (CWW) were investigated by assay of Allium cepa root meristematic cells. The physicochemical parameters of the wastewater samples were also determined. In Allium root growth inhibition test, experimental onion bulbs were cultivated in various concentrations of the CWW and distilled water was used as a negative control. After 72 h, the root tips from the treated bulb were processed for cytological studies by orcein squash technique. The mean lengths of root bundles were obtained and effective concentration (EC) values calculated. The cytotoxic effects on the onion root tips showed strong growth retardation at high concentrations of the effluent with EC value of 5.67%. The mitotic index (MI) 50 rapidly decreased with increasing effluent concentration compared to control. There was significant increase in frequency of chromosome aberrations (stickiness, c-mitosis, vagrant, bridged fragment, binuclei, multipolar anaphase, attached chromosome and laggard chromosome) in root tip meristem cells of Allium cepa at all tested concentrations. At lower concentrations (0.005%), binuclei, (0.5%), vagrant chromosome and (1.0%), bridged fragment were the most common aberrations observed while at higher concentrations, (100 %), c-mitosis, vagrant and bridged fragment were the typical aberrations observed. The results indicate that the effluent samples collected were highly mutagenic. The results of physicochemical analysis revealed that the concentrations of some parameters (turbidity, chemical oxygen demand (COD), biological oxygen demand (BOD), conductivity, total dissolved solid (TDS), total suspended solid (TSS), sulphate, nitrate, phosphate and metals-copper, cobalt, chromium, iron, manganese, magnesium, nickel, cadmium, lead, sodium, potassium and calcium) were above the maximum permissible limit set by world health organization (WHO) and could partly be correlated with the toxicity of wastewater. The findings indicate that the substances contained in the cassava effluents may be toxic to living organisms and may pollute the environment if untreated.

Keywords: Mutagenicity, genotoxicity, cassava wastewater, chromosomal aberration, mitotic index, cyanide, Allium cepa.