Evaluation of heavy metals in the soils of urban and peri-urban irrigated land in Kano, Northern Nigieria

Abstract

Smallholder irrigation for the production of market gardening is important in urban and peri-uban Kano in northern Nigeria. This involves the use of polluted stream water flowing along the major streams in the city. Three streams were selected based on their source of pollutions: Domestic and industrial sources and an ideally non-polluted stream was used as Control. Soil samples were collected from these irrigated sites and analysed for some selected heavy metals including cadmium, chromium, zinc manganese, iron, copper and nickel. The results were compared with the control site and the European Regulatory Standard (EURS). It was found that all the seven heavy metals are higher in the Domestic source pollution (DSP) than in the Industrial source pollution (ISP), prominent among them are Zn, Cu, Fe and Ni, of which their main source is domestic sewage sludge. The high concentration of Cd, Ni and Zn could be associated with tyre wear and combustion of petroleum from the heavy traffic prevalent in this part of the city. The Industrial source pollution stream was found to be less polluted in Mn and Fe which are even less than the control site. There is also continuous accumulation of Fe, Mn and Zn in the DSP sites, this is possibly due to heavy disposal of domestic sewages along the stream. However, the mean concentration of all the heavy metals with the exception of Cd were found to be lower then the European Regulatory Standard, thus there is urgent concern for the authority to look into the continuous accumulation of Cd in especially DSP sites, where the values were above the European Regulatory Standard. Cd can reach human body through crop uptake to the people that consume the crop, this may cause heart and kidney disease.

Keywords: Heavy Metals, Domestic Source Pollution (DSP), Irrigated Land, Industrial Source Pollution (ISP) European Regulatory Standard (EURS)