Heavy metals analysis and toxicity evaluation of some textile and dyeing effluents in Kano, Nigeria using Allium cepa bioassay

Abstract

Insufficiencies in dyeing and textile processing coupled with incomplete sewage treatment system lead to indiscriminate discharge of large amount of dyestuff into water bodies mostly used for irrigation and fishing. These wastes are potentially mutagenic and some are even carcinogenic. In this research, cytotoxicity of three industrial effluents viz; African Textile Manufacturer (ATM), Kofar Naisa and Kofar Mata dyeing centres were evaluated using Allium cepa bioassay. The concentrations of some heavy metals (Cr, Cd, Zn, Fe, Cu, Co, Pb, Mn and Ni) were also determined. Three sets of small onion bulbs were cultivated in 25%, 50% 75% and 100% effluent concentrations (v/v) and a control for each site. Root tips from each bulb were harvested and processed for cytological studies using squashing technique. After 48hrs of exposure, cytotoxic effects of the effluents on root tips (compared to control) showed root growth retardation which was more apparent at higher concentrations. This indicated that, the root growth inhibition was concentration dependent. Number of dividing cells observed and the Mitotic Index (MI) were also concentration dependent. There were decrease in number of dividing cells and MI with increase in concentration of the treatment. The effective concentrations that caused 50% effect (EC₅₀) was 95% for ATM and K/Naisa dyeing points while it was 100% in K/mata dyeing point. Diverse structural aberrations and abnormalities were observed ranging from chromosomal bridge, which was apparent even at low concentrations of the treatment to cytokinesis failure, Micronucleus (MN) and nuclear buds or vacuolated nuclei. Analysis of Variance (ANOVA) showed no significant difference (P>0.05) in mean concentrations of Cr, Fe, Cu and Mn for K/Naisa and K/Mata dyeing centres, but there was statistical difference (P<0.05) for these parameters in ATM. Likewise, there was significant difference (P<0.05) in the root growth of A. cepa exposed to different concentrations of the effluent in ATM and K/Naisa sites but no statistical difference existed in root growth of A. cepa exposed to K/Mata effluents.

Keywords: Allium cepa, Bioassay, Effluents, Cytotoxicity, Mitotic Index