Effects Of Swine Manure-born Heavy Metals On Accumulation Of Heavy Metals In Vegetable Soil And Vegetables

In the intensive animal production, more and more trace elements such as Cu, Zn was added in the feeds of animals to prevent 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 applied in agricultural fields, there will be potentially environmental risks caused by the manure-born metals. Now, although many researches on heavy metal pollution were carried out, most of them focused on the effects of land application of sewage sludge and sewage irrigation on environment and there has been no comprehensive review on the input of metals via livestock and poultry manures. Therefore, this study is to investigate the concentrations and the speciation of heavy metals in poultry and livestock manures, accumulation and transformation of manure-born metals in soil, and effects of manure-born metals on the accumulation of metals in vegetables tissues, and provide some information of reasonable use of poultry and livestock manures in agricultural fields, protection of farmland ecoenvironment and improvement of vegetables quality, by using chemical tests, incubation experiment and pot experiment. 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 Zn, Cu, Mn and As in pig feeds were 324.0 mg/kg, 294.1 mg/kg, 156.2 mg/kg and 5.91 mg/kg, respectively. Nevertheless, much higher contents of Zn, Cu, Mn and arsenic were found in the swine manures, with 1064.0 mg/kg, 1018 mg/kg, 659.9 mg/kg and 59.96 mg/kg, respectively, which was 3-4 times that of feeds. Based on the standard of contamination controlling in sludge for land application (GB42 84-84), all manure samples exceeded the limitations for Cu and Zn, while 35% of samples for arsenic.2, The sequential extraction of heavy metals in the swine manures showed that Cu, Zn and Mn mainly exist in organically bound form and Fe/Mn oxide-bound fractions, less proportion was exchangeable or carbonate fractions. Most of metals were in these four forms, which have highly potential risk to the environment. Arsenicmainly exists in exchangeable form (with 31.2%) , indicating that arsenic is high available to plants and high leachable in soil.3 ^ The results of incubation experiment showed that, the swine maure with high concentration of Cu and Zn used in agriculture may easily induce heavy metal accumulation in the soil, and the soil environment would be polluted by the manure-born metals;as time went on, the exchangeable fraction transformed to more stable forms gradually, while the concentration of carbonate fraction initially rose and then decreased, Fe/Mn oxide and organic fractions rose sequently during the experiment, and the residual fraction was relatively stable with little variation.4> Measurement of the biomass of vegetables showed that, the nutrient status can be improved by using proper quantities of swine manure in agriculture soils and the yields of vegetables would increase, but the growth of vegetables would be inhibited if the manure was long-termly applied with a large quantity.5 > The results of Cu and Zn concentrations in vegetables tissues showed that, the accumulation of Cu and Zn would enhanced with the increasing concentrations of them in soil, the concentrations of Cu and Zn in the roots were higher than that in the above-ground, Zn was more easily accumulated in vegetables than Cu, and the concentrations of Cu and Zn in spinach tissues were higher than that in pakchoi and radish. The concentrations of Cu and Zn in the edible part of tested vegetables were measured up to the Chinese Food Hygiene Standard, except the Zn concentration in spinach treated with swine manure, which reached 21.54 mg kg"2and 24.08 mg kg"1, and exceeded the Chinese Food Hygiene Standard of 20 mg kg'1 for Zn based on fresh weight.6^ Good correlation was obtained between the Cu(or Zn) concentrations in the edible part of vegetables and the extractable soil Cu(or Zn) concentrations extracted by DTPA, which was expected to provide a good estimate of safe soil extractable Cu and Zn concentrations after application of swine manures.