Characterization of Heavy Metals in Livestock Manures

摘要

The use of animal waste for soil amendment is a viable option for waste management. For safe and sustainable management of waste, it is important to assess its chemical speciations. Therefore, an experiment was carried out to compare changes in heavy metals (HM) [cadmium (Cd), mercury (Hg), nickel (Ni), and lead (Pb)] fractions in five types of livestock manures, namely cow, goat, sheep, chicken, and ostrich. The metals were stepwise fractionated into exchangeable, adsorbed, organically bound, carbonate-precipitated, and residual forms by extracting with 0.5 M KNO_3, de-ionized water, 0.5 M NaOH, 0.05 M Na_2 EDTA, and 4 M HNO_3, respectively. Extractability of HM was found to be highly dependent upon the type of waste as well as extracting agent. Manures differed for the release of HM as chicken ＞ ostrich ＞ sheep ＞ cow ＞ goat. Extractions released HM in the order of Ni ＞ Pb ＞ Cd ＞ Hg. For all metals, extracting agents differed in the order HNO_3 ＞ EDTA ＞ NaOH ＞ KNO_3 ＞ H_2O, irrespective of the kind of manure. Carbon content in the poultry manure (both ostrich and chicken) was less than other animals. Poultry manure released more P than goat, sheep, and cow. Chicken manure got the highest pH (9.5) whereas cow manure had the lowest pH value (8.4). Among manures, EC was measured as goat ＞ cow ＞ sheep ＞ ostrich ＞ chicken.