Immobilization and Phytoavailability of As, Cr and Cu in CCA Contaminated Soil, Effect of Poultry Manure Addition

Abstract

The objectives of this study were to evaluate the ability of poultry manure to reduce the levels of soluble, bioavailable and mobile metals forms of As, Cr and Cu in contaminated soil and thus the transferability of the metal to okra (Abelmoschus esculentus) plant, and the long term stability of poultry manure-treated soil. The contaminated soil sample (As 19.80±1.90 mg.kg-1, Cr 190.00±2.10 mg.kg-1 and Cu 108±1.00 mg.kg-1) was treated with various amounts (0, 5, 10, 20 and 30wt%) of poultry manure (pH 6.81 ±0.04, organic matter 5.99 ± 0.11%, P 1522.00 ±4.30 mg.kg-1 and N 0.40 ± 0.10%), re-wetted to 60% of its water holding capacity and incubated at ambient temperature (28-31oC) for 2 weeks. Single extractions of test soil samples with deionised water and 0.01M CaCl2 solution and sequential extractions following the BCR protocol of the test soil samples revealed reductions of up to 40% and about 60% in the bioavailable and water-soluble metal fractions respectively and in the mobile metal pools. The level of metal uptake by okra decreased with increase in the level of poultry manure application and varied in the order Cu > Cr > As. The transfer coefficient of the metals from the soil to okra plant varied from 0.14 to 0.06 for As, 0.20 to 0.007 for Cr and 0.06 to 0.04 for Cu in unamended and poultry manure amended soil samples respectively, while the translocation factor was about the same order of magnitude; Cr (50%) and Cu (30%) in unamended and poultry manure amended soils, but varied from 54% in unamended soil to 85% in poultry manure amended soil for As. Post-harvest acid treatment of the test soil samples did not reveal marked release of the metal fraction fixed in the soil matrix following poultry manure addition to the contaminated soil