| Summary: | 碩士 === 國立屏東科技大學 === 環境工程與科學系 === 91 === The Characteristics of Heavy Metals in Several River Sediments
Mao-Wen Tiao and Fang-Yin Lee
Department of Environmental Science and Engineering,
National Pingtung University of Science and Technology
Abstract
This project aims to study the content, distribution, chemical forms, and desorption characteristics of heavy metals in three river sediments. The samples were collected with a self-developed sampler from Feng-Shan, Dian-Bao, and Ah-Kung-Dian Rivers in Kaohsiung County. The basic properties were determined, including pH, organic matter, particle-sized distribution, cation exchange capacity, base saturation and heavy-metal content. In addition, the sequential extraction procedure developed by Tessier et al. was used to study the fractionation and mobility of heavy metals. The cumulative desorption curves were applied to investigate the release of heavy metals into water. The results showed that the sediments were highly contaminated with Cr, Zn, Ni, Pb, Cu, and mostly accumulated in the upper layer. In descending order, the heavy-metal contents were Cr > Zn > Ni > Pb > Cu in Feng-Shan River, Zn > Ni > Pb > Cr > Cu in Doan-Bao River, and Zn > Cr > Cu > Pb > Ni in Ah-Kung-Dian River, respectively. The results of sequential extraction indicated that Ni existed mainly as residual (average 49%) and carbonate forms (21.1%), Pb as residual (30.3%) and carbonate forms (21.1%), Cu as oraganic (32.4%) and residual forms (27.1%), Zn as Fe-Mn oxide (27.4%) and carbonate forms (45.3%), Cr as Fe-Mn oxide (36.4%) and residual forms(43.5%). The mobility factors of Feng-Shan River in descending order were Pb ( 38.8% )＞Ni ( 31.5% )＞Cu ( 25.9% )＞Zn ( 24.3% )＞Cr ( 8.3% ), while those of Ah-Kung-Dian River were Zn ( 68.5% )＞Pb ( 43.7% )＞Ni ( 33.5% )＞Cu ( 16.2% )＞Cr ( 11.1% ), and those of Doan-Bao River were Zn ( 44.2% )＞Pb ( 37.7% )＞Cu ( 35.4% )＞Ni (29.2% )＞Cr ( 9.5% ). Because the majority of metals existed as residual, carbonate-associated, and Fe-Mn-associated forms, the mobility factors of most heavy metals were lower than 45%, with Cr the lowest above all. The phenomenon remained the same with the release rate of heavy metals (＜6.69% ) in the desorption experiment. This accorded with the lowest rate of Cr (1.78%). Due to long-term pollution, all heavy metals could not yet keep balanced after 90-day desorption experiment. The fact that certain amounts of heavy metals remained in all sediments after desorption indicated that it might be difficult to remove metals completely from their contaminated sediments under natural circumstances.
Key word：Sequential Extraction Procedure, Desorption, Mobility Factor
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