Content and fractionation of heavy metals in livestock manures in some urban areas of China

Samples of livestock manures were taken from intensive farms in some urban areas of China to study content and fractionation of heavy metals. Results indicated that Cu, Zn, Cd, As, Ni, Cr, Pb and Hg content in these livestock manure samples varied greatly, with averages of 377.5, 1 610.4, 0.72, 7.79, 9.77, 22.51, 6.31 mg·kg-1and 0.06 mg·kg-1, respectively. The content of Cu, Zn, Cd and As was significantly higher in pig manure than in poultry manure and in cow and sheep dung, while Cr content in poultry manure was the highest among all samples. There were 59.84% and 95.08% of pig manure samples in which Cu and Zn content exceeded the National Control Standards of Contaminants in Agricultural Sludge, respectively. Based on the Standards of Guidelines for the Safe Use of Animal Manure in Vegetable Field, Cd, Ni, Cr, Pb and Hg in the pig manure samples were all safe, while for As there was only 3.28% of samples exceeding the limit.However, for Zn, Cu and As, 78.69%, 74.59% and 9.84% of pig manure samples exceeded the limits, respectively. Copper or Zn content decreased in order of nursery pig manure>growing-finishing pig manure>sow manure. The content of As in growing-finishing pig manure was higher than that in nursery pig manure and sow manure, while Cd content was higher in sow manure than in growing-finishing pig manure and nursery manure. In addition, water soluble Cu and As content accounted for 30.47% and 12.19% of the total, respectively, while EDTAextractable Zn and Cu were 35.96% and 48.93% of the total, respectively. The high mobility of Cu, Zn and As in pig manure might increase their risk of releasing into the environment.