ABSTRACT

Batch sorption and incubation experiments were carried out in the Soil Science Laboratory of Michael Okpara University of Agriculture, Umudike (MOUAU) to evaluate the effect of cow dung, poultry manure and cocoa pod on sorption of heavy metals; amendment and heavy metal effect on soil chemical properties. Batch sorption experiment was Completely Randomized Design (CRD) using two factors; (A) amendment with cow dung, poultry manure and cocoa pod as rates and (B) time with 15 minutes, 30 minutes and 60 minutes also as rates with three replications. Also, an incubation experiment was CRD consisting of twelve treatment combinations replicated three times. Soil samples used in the study were collected at the depth of 0-20 cm from arable land within MOUAU. All the amendments used were sourced locally. Batch study was conducted at room temperature using batch adsorption techniques. Heavy metals solution used for the batch study was prepared at the concentration of 100 mg/L. Whatman No.1 filter paper was used to filter heavy metal solution. Incubation experiment was also carried out at the same temperature for thirty days. The soils were amended with 1g of each amendment and contaminated with heavy metals at the rate equivalent to 60 mg/kg and wetted throughout the incubation period. Available metal was extracted using 50 ml of 0.05 ml EDTA solution at the end of incubation and analyzed for heavy metal concentration. Routine chemical analyses were carried out on the soils after incubation using standard laboratory procedures. The data obtained were subjected to analysis of variance (ANOVA) using Genstat edition 3 (GenStat, 2007) and the means separated using Fisher’s Least Significant Difference (LSD) at 5% level of probability. Batch study revealed no significant effect of contact time on sorption of metals while the amendments had significant effect with time amendment interaction being significant only on adsorption of copper. Highest Cu, Pb and Zn (2.34 mg/g, 2.41 mg/g and 2.39 mg/g) was adsorbed by cow dung, cocoa pod and cow dung at 60, 15 and 30 minutes of contact times respectively while the least; 1.84 mg/g, 0.87 mg/g and 1.99 mg/g were sorbed by poultry manure at 30, 15 and 30 minutes of contact times respectively in batch study. Isotherms of the three metals obtained in all the amendment had H shape. All the amendments had significant effect on extraction of the metals with the highest amount extracted from controls without amendments while the least Cu (30.33 mg/kg), Pb (36.17 mg/kg) and Zn (37.17 mg/kg) were extracted from poultry manure, cocoa pod and cow dung amended soils respectively. Also, the treatments had significant effect on soil chemical properties with the effect of organic amendments in combination with heavy metals being virtually higher than the sole effect of heavy metals in all the soils. Generally, all the amendments showed good potential in binding heavy metals in both soil and aqueous solution and improving soil chemical properties.