| Summary: | 碩士 === 國立中興大學 === 土壤環境科學系 === 92 === Suitable use of organic fertilizers usually can improve the physical, chemical and biological properties of soil, and also can reach the goals of recycle and reuse of resources, however, some organic fertilizers contain excess amount of heavy metals lead to reduce the qualities of soil and crop. At present, the Chinese National Standards(CNS) method for determining the content of heavy metals in organic fertilizers used by Bureau of Standards, Metrology and Inspection(BSMI) are distributed in different sections and chapters. In addition, there are different digestion methods for different heavy metals cited in CNS standards. The analysis methods used by Taiwan Agriculture Research Institude(TARI) and Soil Survey and Testing Center(SSTC) are also different from that used by the Bureau of Standards, Metrology and Inspection(BSMI).Therefore, it is easy to result in confusion and argument about data between inspectors and fertilizer manufactures.
The purposes of this study are to compare the results obtained by three organizations(BSMI, TARI and SSTC) for the contents of heavy metal in ten organic fertilizers, and to compare the effectiveness and suitability of CNS, acid digestion(HNO3-HClO4-HCl) and dry ash methods to determine the content of Cu, Zn, Cd, Cr, Ni, and Pb for five animal composts and two other composts using Inductively coupled plasma atomic emission spectrometry (ICP-AES). In addition, the effects of matrix in samples on the analysis method were evaluated by spike addition with standard heavy metal solution. For development a suitable test method on determination of heavy metal contents, a factor experimental designs using acid digestion method was conducted, including four amounts of sample(0.1 g, 0.2 g, 0.4 g, and 0.6 g ), two concentrations of HCl(2N and 3N), three mixture of acids of HNO3-HClO4 (5:1, 5:2, and 7:1) and two digestion times (8 hour and clarification condition).
Result showed that different test values of heavy metals of the same ten organic fertilizers were found even using acid digestion, obtained from the result of the three organizations. The method of acid digestion was found to be the most suitable and correct method to measure the heavy metal contents in organic fertilizers due to higher percentage of recovery in spiking test and more clarified solution were obtained, however, the amount of sample used was less than other methods. After evaluation, the acid digestion method using ICP-AES determination was recommended to be used to measure the contents of heavy metal in organic fertilizers, and four analysis conditions were suggested as follows: (1)sample size is 0.4 g, (2)the ratio of acid is HNO3:HClO4=5:1, (3)the concentration of HCl is 2 N and (4)the digestion time is heat required to sample until almost clarification.
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