Research On Soil Accumulation Effect And Environmental Impact Of Heavy Metal In Pig Feed And Swine Manure

In the intensive animal production, more and more trace elements such as Cu, Zn was added in the feeds of animals to prevem disease, improve feed efficiency and make them grow faster. Due to low bioavailability of these elements in animal bodies, most of them were excreted to the environment with animal feces.When the manures containing high concentrations of these heavy metals are appplied in agricultural fields, there will be potentially environmentm risks caused by the manure-born metals.Heavy metal into the plant body has became the most important way to pollute the environment and endanger human health. However, the biological activity and environmental behavior of heavy metals in soil depends not only with the total amount, but also on their chemical form in the environment. Therefore, it is very significant to analyse the form change, mobility and biological toxicity of heavy metals by research the formation distribution and its influencing factors of heavy metals in the compost soil.Now, although many researches on heavy metal pollution from livestock manure were carried out, most of them focused on the study of total content of heavy metals in soil and its evaluation and there has been rare comprehensive review on the effects of the bioavailability and speciation of heavy metals in the soil on swine manure composting. This paper provides some infomation of reasonable use of poultry and livestock manures in agricultural fields, protection of farmland ecoenvironment and improvement of vegetables quality, by analyzing the contents and fractionation of heavy metals in pig feeds and swine manures and the impact of the content and chemical speaciations of heavy metals in compost soil from intensive livestock farms in the suburb of Zengcheng were studied. The main results are summarized as follows:1. The results of heavy metals contents in pig feeds and swine manures showed that the average contents of Cu, Zn and As in pig feeds are high,which was4-7times that of feeds. Based on the control standards for pollutants in sludges from agricultural use(GB4284-84), all manure samples exceeded the limitations for Cu and Zn;based on the control standards for urban wastes for agricultural use(GB8172-87), all the grower manure samples exceeded the limitations for As, exceeding by40%.2. The sequential extraction of heavy metals in the swine manures showed that Cu, Zn and Pb mainly exist in weak acid soluble fractions and reducible fractions, less proportion was organic matter fractions and residual fractions.Most of metals were in these three forms with strong activity and leaching rate, which have highly potential risk to the environment.3. The results indicate that pig manure compost(PMC) can greatly improve the soil PH, CEC and the content of soil organic matter,which were all decreased gradually with the increase of soil depth. The concentration of Cu and Zn in soil is increased during pig manure composting, decreasing from the soil surface layer to bottom.However, the concentration of Pb and Cd, Hg and As in compost soil fluctuate comparatively little with the soil depth.The pollution evaluation of heavy metals pollution of both compost soil indicate that apart from slight pollution of Cu with the depth of10cm in the vegetable garden soil profile, all the other compost soil was not polluted by Cu, Zn, Pb and Cd, Cr, Hg and As.4. The mass fraction of secondary phase of each element in the composting vegetable garden soil and composting orchard soil in descending order:Cu>Pb>Zn、Pb>Cu>Zn, respectively. The bioavailability and mobility of Cu and Pb are highest in the studies three heavy metals, with potential ecological risks, while Zn is relatively more stable and hard to release.5. Good correlation was obtained between the speciation concentrations of heavy metals and the total content of heavy metals in compost soil, the speciation concentrations of heavy metals in compost soil were affected together by several relative factors,such as PH, organic matter, CEC,sand,silt and clay. Among them, the total amount of heavy metal is probably the most critical factor determining the speciation concentrations of heavy metals, followed by organic matter, PH and CEC.6. The heavy metal content in vegetables group of the purple perilla leaf and sweet potato was higher than that in their plant stem, with particularly significant the heavy metal content in the plant stem as high as leave2to9times.Based on the Maximum levels of contaminants in foods (GB2762-2005), in addition to the content of As in the group of purple perilla leaf exceeded the standard in all the fruit and vegetable samples studied, other fruit and vegetable samples satisfied the standard.