SOME HEAVY METALS IN PLANTS IRRIGATED WITH SEWAGE EFFLUENTS

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Department of Engineering

ABSTRACT
This study investigates the concentrations of certain metals absorbed by crops when irrigated with sewage effluents. Amaranthus, tomatoes and maize crops were flood-irrigated with A.B.U., Zaria waste stabilization pond effluents for about 4 months at application rate of 80 litres per day per plot of 4m x 2m. Tapwater was used as control irrigation water. The concentrations of heavy metals including Zn, Mn, Pb, Cd and B in the sewage effluents and the tapwater were determined, in addition to the initial concentrations of these metals in the soil. Also, the cumulative absorption of these metals in the various parts of the experimental crops were determined during the periods of irrigation. It was found that A.B.U. sewage effluent contained slightly more Zn, Mn, Pb, Cd and B than the tapwater. Although the Pb, Cd and B concentrations absorbed by various tissues of the test crops were more when the crops were irrigated with sewage effluents than with tapwater, the difference was not statistically significant. However, the Mn concentrations absorbed by various parts of the test crops were significantly higher in the tapwater than in sewage effluents irrigated crops. The results show that different crops absorbed these metals at different rates and that the absorption of the metals differ from part to part for each crop. Generally the roots of the test crops absorbed the highest concentrations of Zn, Pb, and Cd followed by stem. However, the Mn and B absorption were highest in the leaves than the remaining parts in all the test crops. The maize grains and the tomato fruits contained the lowest concentrations of all the elements investigated. Although the heavy metal concentrations absorbed by the different parts of the crops increased (except Mn) with increasing sewage application, the concentrations of these metals absorbed during the period of study were within the permissible limits. However, the effect of longer period of. investigation on the absorption of these metals should be investigated.