中文摘要：

在湖北恩施渔塘坝土壤硒分布的调查过程中，发现不同地段田地土壤中存在异常高硒样品。其硒含量变化范围是346～2018mg／kg，平均（899±548）mg／kg（n=11），相对于坝内成土基岩和耕作土硒含量0．5mg／kg与3．5mg／kg的水平而言，表明这些土壤硒受到了外来源硒的严重污染。扫描电子显微镜的观察表明，这些土壤样品中均有大量晶体状自然硒的出现，其特征类似燃煤型成因的自然硒，证实了上世纪50年代后期恩施当地居民石煤火熏土作肥的耕作方式，并直接导致了田地土壤硒的骤然增加。渔塘坝当地居民在1963年间的硒中毒爆发性流行，乃至恩施地区人畜硒中毒的普遍流行，极可能是人为因素引起。

英文摘要：

During a field-screening study to investigate the distribution of Se in soils and rocks in Yutangba, the anomalous levels of Se in soils were found in different croplands, which range from 346 to 2018 mg/kg, with an average of 899 ±548 mg/kg （n = 11）, significantly greater than the average of 3.5 mg/kg Se in soil. SEM obserations showed that native Se crystals occurred in these samples, which are very similar to those reported Se crystals derived from natural conbustion of stone coal and found in abandoned stone coal spoils. The results indicated that the source of Se in cropland is different from that of soils, which was not cultivated by human activities, and confirmed that local villagers ever had the custom of baking soil on the stone coal fires and then the baked soil was dispersed on the cropland as a fertilizer to improve soil fertility. This cultivating manner ever used by the villagers lived in Yutangba and other places introduced a large amount of Se into their cropland and made it further accumulated in their food chain. The occurrence of native Se crystals in Yutangba cropland explains the reason why sudden incidence of human Se poisoning occurred in some places like Yutangba in Enshi rather than in the whole high-Se areas.