蛇紋岩土壤之特性及其重金屬含量偏高問題

Characterization and High Heavy Metal Content Problems of Serpentinitic Soils

許正一(Zeng-Yei Hseu) ； 蔡衡(Heng Tsai)

《臺灣鑛業》 63卷1期 (2011/03) Pp. 12-26

https://doi.org/10.30014/TMI.201103.0003

摘要

蛇紋岩是超基性火成岩經熱水蝕變而成，其所含的鐵鎂質原岩結晶構造以島狀矽酸鹽為主，故較易風化崩解，且鎂含量高於鈣，而鉻、鎳等重金屬含量偏高，其纖蛇紋石呈纖維狀。蛇紋岩生態系主要的環境問題為土壤沖蝕、土壤鈣/鎂比值偏低且磷與鉀有效性低、石棉纖維逸散、土壤與地下水重金屬污染等。無論重金屬是來自人類污染行為或源自地質環境，只要暴露在生態系統中，對人類健康的潛在危害都是值得重視的問題。全球一般土壤中的鉻、鎳含量分別為84 mg/kg、34 mg/kg，但臺灣蛇紋岩土壤中的鉻與鎳含量不僅高於一般土壤，且會遠高於土壤及地下水污染整治法中的土壤污染管制標準（鉻：250 mg/kg，鎳：200 mg/kg）之10倍以上。鉻、鎳的礦物來源不同，鎳的溶解度與移動性遠高於鉻，而兩者均會隨著風化作用與地形的改變而變得較易溶解。臺灣的蛇紋岩生態系需要面臨的挑戰為水土保持問題的解決、土壤與地下水潛在污染源查證與驗證、與健康風險評估的因應，所以需要落實這些基礎調查研究，才能讓法令在執行上有科學根據，並防範未來在此類場址所發生之整治或執法困擾，進而提升政府施政效能。

關鍵字

蛇紋岩 ； 土壤 ； 鉻 ； 鎳 ； 土壤及地下水污染整治法 ； 生物有效性

並列摘要

Serpentinites are derived from ultramafic igneous rocks through hydrothermal alteration, which original rocks are island silicate framework and high in Fe and Mg. Serpentinites are weakly resistant in weathering and characterized with high Mg and low Ca and abundant levels of Cr and Ni, and their chrysotile is fiber-shaped. The major environmental problems of serpentinitic ecosystem are soil erosion, low Ca/Mg ratio and low availability of P and K in the soil, emission of asbestos fiber, and soil and groundwater contamination with heavy metals. Through environmental exposure, heavy metals not only from anthropogenic sources but also from geologic origins cause a clear risk potential of human health. The average Cr and Ni contents in global soils are around 84 mg/kg and 34 mg/kg respectively. However, Cr and Ni contents of serpentinitic soils in Taiwan are clearly higher than those of global average and excessive with 10 folds of the soil pollution control standards (Cr: 250 mg/kg, Ni: 200 mg/kg) regulated in the Soil and Groundwater Pollution Remediation Act (SGPRA). The mineral origins of Cr and Ni are different. The solubility and mobility of Ni are always higher than those of Cr. Nevertheless, both metals tend to be soluble associated with weathering and landscape changes. New challenges of serpentinitic ecosystem in Taiwan are problems of soil and water conservation, identification and verification of soil and groundwater contamination source, and requirement of health risk evaluation. Therefore, it is necessary to be carried out basic study and survey for serpentinitic soils for applying scientific evidences in regulating the SGPRG, facilitating site remediation, and promoting policy efficiency.

並列關鍵字

Serpentinite ； soil ； chromium ； nickel ； Soil and Groundwater Pollution Remediation Act ； bioavailability