Heavy Metal Pollution And Environmental Risk Assessment Of Livestock Manure

The safe and rational use of organic fertilizers plays a role in recycling agricultural production, however, which is still experiencing technical difficulties during the current production. This research was undertaken in order to determine and analyze various heavy metals present in organic fertilizer sampled in Zhejiang Province of China. The accumulation and translocation of heavy metal in commercial organic fertilizers applied to soils was then investigated by using long-term fertilization experiments in Food-Oilcrop rotation systems and Food-Economic crops rotation cropping systems. By further analyzing heavy metals safety limited quantity in organic fertilizer at home and abroad and evaluating soil environmental capacity for heavy metals in different soils, the pollution status of heavy metal in commercial organic fertilizers and their potential ecological risk to the environment were finally discussed. The present findings provided us a clue for the use of organic fertilizer in safe. The results were listed as following:(1.) The results of the pollution status of heavy metal in commercial organic fertilizers reveal that it is commonly to find commercial organic fertilizers polluted by heavy metals, which have a concentration of heavy metal higher than the safety limited quantity. The mean concentrations of metals showed that there were significant differences among seasons and samples with different raw materials. The exceeding standard rate of metals of fertilizes samples produced from different raw materials were found to be in the order of pig manure>manure mixture>chicken manure and cattle manure. Based on the standard of NY525-2012 Organic Fertilizer by the Ministry of Agriculture in China and the limited standards of heavy metals in compost established by Germany, it could be found that the mean exceeding standard rate of Cu, Zn and As in pig manure fertilizers collected in spring was 95.35%, 88.37% and 58.14%, respectively. In the pig manure fertilizers collected in Summer, however, the mean exceeding standard rate of Cu, Zn and As decreased with a value of 89.19%、81.08%、24.32%, respectively. Besides, it could be noted that the concentration of nutrients and organic matters in organic fertilizers produced from different raw materials showed significant differences. Indeed, the pig manure fertilizers have a highest content of nutrients while the cattle manure fertilizers exhibit a highest content of organic matter.(2). The results of a 5-Years located experiment in the Food-Oilcrop rotation systems showed that the total nitrogen, the available P, the available K and the organic matter in soils showed a increasing trend after organic fertilizer applied and their concentrations increased with the increasing dosage of the applied fertilizers. However, we also noted that the Cu, Zn and Hg contained in soil arable layer exhibited an increasing trend after the application of organic fertilizer. Among all the metals, Cu, Zn and Hg have a relatively higher pollution degree and potential ecological risk indexes, both of which increased as the application dosage of organic fertilizer increased. When a low dosage (2625 kg/hm2) of organic fertilizer was applied, both Cu and Zn in soils are determined to be a severity level for pollution degree and a mild level for the ecological risk to the environment; whereas, the Hg are determined to be a mild level for pollution degree and a moderate level for the ecological risk to the environment under the same condition. The trials with an organic fertilizer application dosage of 5500kg/hm2 showed a completely same result as that with a low dosage of organic fertilizer. When the dosage of organic fertilizer applied increased to a high level (8125kg/hm2), the pollution degree of Cu and Zn in soils is determined to be a mild level and a severity level, respectively. However, both Cu and Zn in soils are determined to be a mild level for the ecological risk to the environment after a high dosage of fertilizers used. Indeed, just like other two trials, the Hg are determined to be a mild level for pollution degree and a moderate level for the ecological risk to the environment after fertilization with a high dosage of fertilizers. According to the above-mentioned results, it could be concluded that the pollution degree and ecological risk index of heavy metals in organic fertilizers can increase with the increasing of the application dosage.(3). As shown in results of a 5-Years located experiment in the Food-Economic crops rotation cropping system, fertilization with organic fertilizers increased the total nitrogen, the available P, the available K and the organic matter in soils, decreased the soil pH and alleviated the soil acidification. As same as that found in the Food-Oilcrop rotation systems, the heavy metals accumulated in arable soil layer increased with the increasing dosage of the applied fertilizers. The Zn, Cr and As showed a obviously increasing trend among all metals. Among all the metals, Cu、Zn、 Pb and Hg have a relatively higher pollution degree and potential ecological risk indexes compared with other metals. When a low dosage(10.5 t/hm2) of organic fertilizer was applied, all Cu、Zn and Pb in soils are determined to be a severity level for pollution degree and a mild level for the, ecological risk to the environment; whereas, the Hg are determined to be a severity level for pollution degree and a moderate level for the ecological risk to the environment under the same condition. When the application dosage of organic fertilizer increased to a high level (18 t/hm2), the pollution degrees and the ecological risk indexes of all Cu, Zn and Pb in soils are found to be mild. Under the same condition, the Hg is determined to have a high level for pollution degree and a moderate level for the potential ecological risk.(4) As shown in results of a 5-Years located experiment in the Food-Economic crops rotation cropping system, When use level of organic fertilizer at 18 t/hm2,that would had evident effects on changing of mercury content. According to estimate that application fertilizer 21 times continuously would beyond secondary standard. Manure application within the scope of rational fertilization, while improving soil fertility and heavy metal contamination risk can be effectively controlled.