| Summary: | 碩士 === 中興大學 === 土壤環境科學系所 === 95 === With industrial development and technical advance, some of the heavy metals used in artificial activities enter soil and cause contamination by improper handling. The most common method to determinate heavy metals in polluted soils is chemical extraction with different reagents. Chemical extractions includes single extractions and sequential extractions. Single extraction procedures extract heavy metals in soil by only one step, are usually time-saving, with easier process, and they can choose reagents for different purposes. Single extraction is suitable for differentiate mobility and bio-availability of heavy metals. Sequential extraction procedures extract different forms of heavy metals step by step, but they are time-consuming and with complicate process. However, sequential extraction procedures provide complete informations of different heavy metals forms in soil. It is possible to evaluate short-term and long-term impact of heavy metals against environment by sequential extraction results.
Recently, Taiwan conforms aqua regia digestion to regulate the control standard of heavy metal content in soil. However, this method cannot directly reflect the threat to environment by heavy metals. There are two objectives for this study. One is to compare the results of BCR and Tessier sequential extraction applying on six contaminated soils with different heavy metals content to understand the fractionations of the heavy metals. The other purpose is to apply seven single extraction procedures including H2O, 0.1M CaCl2, 0.11M HOAc, 0.005M DTPA, 0.05M EDTA, 0.1M HCl, 0.12M HNO3 and XRF detection on 30 samples with different heavy metals content, to compare the results from single extractions and aqua regia digestion and to evaluate the practicability of single extractions replacing aqua regia digestion by double sampling design.
Results of sequential extractions show that most of cadmium exists in exchangeable form than other heavy metals. In soils with low heavy metal concentration, most of copper and zinc are residual or reducible. In soils with high heavy metal concentration,most of copper and zinc would distribute in exchangeable form. Most of nickel and lead distribute in reducible or oxidisable form. Aqua regia digestion would overestimate the impact. chromium only distribute in reducible, oxidisable, and residual form. Few of chromium exist in exchangeable form, and it is harmless to the environment. Two sequential extractions lead to different results because of variation in methods. BCR procedure is an ideal method in terms of operation. Amont of heavy metals extracted by different single extraction reagent is in the following order: 0.1M HCl≥ 0.12M HNO3＞0.05M EDTA＞0.005M DTPA＞0.11M HOAc＞0.1M CaCl2＞＞H2O. 0.1M HCl extraction shows significant regression relationship between aqua regia digestion of Cd and Pb in these 30 samples. While results of 0.05M EDTA extraction show good regression relationship between aqua regia digestion of Cd, Cu and Pb. XRF detection shows the best regression relationship between aqua regia digestion in Cr, Ni, and Zn. It also shows significant regression relationship with aqua regia digestion of Cu and Pb. Applying double sampling to single extractions and aqua regia digestion shows 0.1M HCl can replace aqua regia digestion in Cd and Pb contaminated soils, XRF detection can replace aqua regia digestion in Cr, Cu, Ni or Zn contaminated soils. Analytical outlay can be saved and sample amount can be increased by applying two methods on specific polluted samples.
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