THE EFFECTS OF TANNERY SLUDGE ON HEAVY METALS CONCENTRATION IN CEREALS ON SMALL-HOLDER FARMS IN KANO, NIGERIA

Abstract

The effects of the use of tannery sludge as soil amendment material on the heavy metal content in sorghum and millet crops in the Challawa Industrial Estate (CIE), Kumbotso L.G.A. Kano State, were studied. Five farms (each 0.25 ha in size) on which both millet (Ex-Borno) and sorghum (Kaura) crops were cultivated and fertilized with tannery wastes for a period of five years were used for the study. The farm plots were designated TS1, TS2, TS3, TS4, and TS5. Samples (shoots and grains) were collected from these farms for two consecutive years and analysed for the following metals: Cr, Cu, Co, Pb, Mn, Fe, Zn and Ni. Results show that millet crop exhibited higher concentrations of Co, Pb, Zn, Cr and Cu than sorghum, indicating that with repeated applications of tannery wastes as soil amendment material, millet crops could accumulate heavy metals to toxic levels. The heavy metal content of the soils when matched against standard values, were found to be below the tolerance levels and hence posed no danger to man and livestock. Sorghum would be the most appropriate crop to be grown on tannery sludge fertilized lands as it accumulates less heavy metals than millet.