中文摘要：

湖北恩施渔塘坝是中国人群硒中毒爆发性流行的典型病区.使用改进的7步连续化学浸提技术,对渔塘坝土壤硒进行了水溶态、可交换态、有机态、元素态、酸性提取态、硫化物/硒化物态和残渣态硒的提取,并应用氢化物-原子荧光法测定了土壤总硒和各结合态硒.结果表明,渔塘坝高硒土壤中硒结合态分布基本可以分为4种类型,或以有机结合态硒为主,或以元素态硒为主,或是有机结合态和元素态硒为主,亦或是有机结合态和硫化物/硒化物硒为主,可交换态和元素态硒次之.上述硒的结合态分布特征说明,渔塘坝土壤硒来源或以人为引入硒为主,或以富硒碳质岩石的风化来源为主.渔塘坝旱地土壤中元素态硒（多以自然硒晶体形式出现）的普遍分布,揭示了人为来源硒的引入是导致田地土壤高硒的主要原因.也就是说,20世纪60年代初期,当地村民耕种田地的施肥方式是引入硒的主要途径.

英文摘要：

Yutangba is one of the typical high-Se areas in Enshi Prefecture in China, where a sudden incidence selenium poisoning occurred in 1963. Using a modified sequential chemical-extraction technique, seven operationally defined selenium fractions were determined in soils from Yutangba, which were defined as water-soluble, ligand-exchangeable, base-soluble, elemental, acetic acid-soluble, sulfide/selenide, and residue. Bulk selenium in soil and selenium concentration in each fraction were measured by hydride generator-atomic fluorescence spectrometry （HG-AFS）. The. results show that selenium fractions in soils from different locations of Yutangba can be divided into four types according to the dominant fractions of selenium, i. e. elemental, organic-bound, elemental plus organic-bound, and organic-bound and sulfide/selenide with some ligand-exchangeable and elemental Se. The distribution of selenium fractions indicates that the source of selenium in Yutangba soils is diverse, and could be introduced by local farmers via traditional cultivation methods, or supplied from the weathering processes of Se-rich carbonaceous rocks exposed in the north part of Yutangba. Because of the occurrence of native Se crystals in soils from different cropland sites, we propose that Se in cropland soil is mainly introduced by local villagers＇ cultivation methods. Therefore, the source of the Se introduced in the 1960＇s to Yutangba soils was mainly anthropogenic.