蛇紋石生態系中巨量元素與微量元素在土壤與植物體之含量探討

Macro and trace element contents in soils and plants of a serpentine ecosystem

陳念祖(CHEN NIEN CHU)

指導教授 ： 許正一

國立屏東科技大學/工學院/環境工程與科學系所/碩士(2011年)

https://doi.org/10.6346/NPUST.2011.00071

摘要

蛇紋岩土壤為超基性岩類母質所風化，其土壤有效性氮、磷、鉀偏低，Ca/Mg比值偏低，並含有高濃度的鉻、鎳、鈷等重金屬，其濃度可遠超過台灣的土壤污壤管制標準，而矽和鈣則含量較低，因此使得一般植物不易生長。蛇紋岩土壤的重金屬雖非人為污染所致，但一樣會影響生態環境與人體健康，因此本論文採取花蓮萬榮某一廢棄蛇紋岩礦場之7種優勢植物及根域土壤，這7種植物為豬屎豆、五節芒、銀合歡、咸豐草、葛藤、印度草木犀及加拿大蓬等。研究目的為探討蛇紋石生態系中巨量與微量元素在土壤與植物中的元素含量，並以序列萃取法及單一試劑萃取法測定不同型態之重金屬，以了解植物吸收重金屬之含量及不同部位的吸收量，評估植物之元素組成與植物有效性。研究結果顯示，多數蛇紋岩土壤之Ca/Mg比值小於1.0，為典型蛇紋岩土壤的特徵，而土壤中鉻的含量為559-723 mg/kg，鎳為691-1220 mg/kg，皆已超過現行的土壤污染管制標準甚多。在重金屬型態劃分中，鉻與鎳主要被固定在礦物晶格內，故集中在殘餘態，而元素間移動性鎳大於鉻，在DTPA萃取量方面，仍是鎳高於鉻，其與序列萃取之型態分佈趨勢差異相符，表示蛇紋岩土壤中的鉻不易被植物所攝取，而HCl萃取也與DTPA萃取趨勢相似。受到蛇紋岩土壤母質特性之影響，植體中重金屬濃度也較一般植物高，錳含量為10.4-69.4 mg/kg，鉻含量為6.08-36.9 mg/kg，鎳含量為8.52-51.4 mg/kg，植體中的錳與鉻大部分累積於根部，而鎳則明顯累積在葉片，顯示本研究區植物可能具有潛力成為鎳累積之植物，因為葉片之於根部之鎳轉移係數可大於1.0，其中又以豬屎豆的2.27最高。

關鍵字

蛇紋岩土壤 ； 超基性岩類 ； 重金屬 ； 植物有效性

並列摘要

Serpentinitic soils from ultramafic parent rocks are characterized by low availability of N, P, K, and Ca/Mg and extremely high contents of heavy metals like Cr, Co, and Ni. These metal levels in the serpentinitic soils can be much higher than the soil pollution control standards (SPCS) of Taiwan. Additionally, low contents of Si and Ca causes to poor growth of general plants. The heavy metals in the serpentinitic soils are not anthropogenic, but they have potential risk to ecosystem and human health. Therefore, this study selected an abandoned site of serpentine at Wang-Ron, Hualiean to collect 7 species of plant and the corresponding soils in the root zone. The plants include Crotalaria zanzibirica, Miscanthus floridulus, Leucaena leucocephala, Bidens pilosa, Dolichos lobatus Willd., Melilotus indicus and Conyza Canadensis. The purposes are to explore element contents in the soils and plants, to fractionate heavy metals by sequential extraction and single extraction, to understand the plant uptake of the elements and their compartmentation in different plant tissues, and evaluate the phyto-availability. The experimental results indicated that the Ca/Mg ratio was lower than 1.0 in most cases of soils and reflected the typical characteristics of serpentinitic soils. The concentrations of Cr and Ni ranged from 59 to 723 mg/kg and from 691 to 1220 mg/kg respectively, which greatly exceeded the SPCS. Regarding solid fractionation of Cr and Ni, the dominant phases of Cr and Ni are the residual forms which are fixed in the mineral framework. The DTPA- and HCl-extractable amounts of Ni was higher than that of Cr, which difference in trend betwee elements is the same to that by sequential extraction. Therefore, Cr is hard to be absorbed by the plants. The heavy metal contents in the studied plants were higher than those in the other plants. The concentrations of Mn, Cr, and Ni in the plant ranged from 10.4 to 69.4 mg/kg, from 6.08 to 36.9 mg/kg, and from 8.52 to 51.4 mg/kg. In addition, most Mn and Cr in the plant accumulated in the root, while Ni was in the leaves. This study elucidates that the plant may be potential accumulators of Ni, because the transfer factor (TF, leaf/root) of Ni is higher than 1.0, particullarly for Crotalaria zanzibirica with TF 2.27.

並列關鍵字

Serpentinitic soil ； ultramafic rock ； Heavy metals ； Phytoavailability

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