Effect of irrigation on heavy metals content of wastewater irrigated fluvisols along River Tatsewarki, Kano, Nigeria
There is an urgent need to educate farmers on the dangers of the presence of heavy metals in soils as well as the quality of irrigation water especially if it comes from tanning industries for increased crop production. Accordingly, soil and irrigation wastewater study was conducted to assess the concentrations of heavy metals in wastewater irrigated Fluvisols and in the irrigation wastewater itself as well as the relationship between the two. Composite surface soil and water samples including controls were collected and analyzed using standard methods. Analytical results were compared with the controls, the EU and FAO standards. Results indicated that the concentrations of Cu (30.556 to 41.667 mgkg-1), Cd (10.269 to18.687 mgkg-1), Zn (18.687 to 26.010 mgkg-1), Cr (8.848 to 12.14 mgkg-1) and Pb (3.953 to 4.787 mgkg-1) in the soil were non-toxic across the river sections. Results also indicated that the irrigation water contained toxic levels of Cu (0.85 to1.25 mgl-1), Cd (0.36 to 0.72 mgl-1) and Cr (0.47 to 0.67 mgl-1) and is therefore considered unsafe for use. However, it did not contain toxic levels of Zn (0.58 1.06 mgl-1) and Pb (0.22 to 0.25 mgl-1) and it is considered safe for use accordingly. Results also revealed that the irrigation water was responsible for the accumulation of Cr (r = 0.019), Cu (r = 0.151), Cd (r = 0.190) and Pb (r = 0.202) in the irrigated soils but not Zn (r = - 0.214). It is recommended that periodic appraisal of the soils should be embarked upon so as to monitor the toxicity level of the soil to keep it within the present non-toxic level. It is also recommended that the wastewater should be remediated to minimize and control the heavy metal contamination through phytoremediation. These measures are expected to enhance increased and sustainable crop production in the study area.
Key words: Fluvisols, Heavy metals, Irrigation, Wastewater.