The environmental risks posed by heavy metals (HMs) in animal manure are increasing because of the use of trace metals as additives in feedstuffs. Manure samples were collected, and published literature was reviewed in this study to systematically analyze the HMs content in animal manure and compare the results to different sources of animal manures. Results show that the distribution of HMs content in animal manure was skewed. The ranges were between not detected (ND)-147 mg·kg-1 for Cd, ND-1919 mg·kg-1 for Pb, 0.003-2278 mg·kg-1 for Cr, ND-978 mg·kg-1 for As, ND-103 mg·kg-1 for Hg, ND-1747 mg·kg-1 for Cu, ND-11547 mg·kg-1 for Zn, and 1.22-1140 mg·kg-1 for Ni. The means (medians) of those elements were 2.31(0.72) mg·kg-1, 13.5(8.96) mg·kg-1, 36.3(12.0) mg·kg-1, 14.0(3.52) mg·kg-1, 0.97(0.07) mg·kg-1, 282(115) mg·kg-1, 656(366) mg·kg-1, and 21.8 (13.1) mg·kg-1 for Cd, Pb, Cr, As, Hg, Cu, Zn, and Ni, respectively. Means were significantly higher (1-13 times) than the medians. According to maximum limits of Cd, Pb, Cr, As, and Hg for organic fertilizers NY 525-2012, about 12.3% (for Cd), 2.58% (for Pb), 2.76% (for Cr), 20.6% (for As), and 3.69% (for Hg) of the data were above the limits. According to the composting regulations of Germany, about 53.9% (for Cu), 45.7% (for Zn), and 0.59% (for Ni) exceeded the maximum limits. The heavy metal contents in animal manure of different regions differs significantly. As and Cd contents in animal manure in the Shandong Province tend to be higher with their average values at 1.7 times and 10.1 times of the mean contents for national scale, respectively; the heavy metal contents in eastern China tend to be higher. Cd and As contents in animal manure tend to be higher in Northeast and Eastern China, while Cu and Zn contents were higher in Eastern and South China. After comparing HMs content in different sources of manures, we found that Cd, As, Hg, Cu, Zn, and Ni mean contents in pig manure were 1.0-3.0 times, 1.8-6.8 times, 1.1-15.8 times, 4.9-17.5 times, 2.7-12.0 times, and 1.7-2.1 times that of cattle manure, sheep manure, and poultry manure. The Pb content in poultry manure was the highest, with the mean being 2.8, 2.5, and 2.2 times higher than pig manure, cattle manure, and sheep manure, respectively. When recycling animal manure into the crop field, the accumulation rates for Cd were under 0.02 mg·(kg·a)-1 in over 90% of the circumstances and the accumulation rates for Pb were all below 0.15 mg·(kg·a)-1. When applying poultry manure, Cr in soil is easily accumulated with the maximum accumulation rate of 0.28 mg·(kg·a)-1.
Keywords: accumulation rate; content analysis; farmland soil; heavy metal; livestock manure; spatial distribution.