湖北渔塘坝高硒环境中硒的分布、迁移和生物可利用性

DISTRIBUTION, TRANSPORTATION AND BIOAVAILABILITY OF SELENIUM IN YUTANGBA, HUBEI PRONVINCE, CHINA

渔塘坝是中国恩施地区较为典型的高硒地区之一,对整个渔塘坝土壤硒、植物硒和水硒及其变化趋势的研究表明,含硒较高的土壤和植物主要分布于西北部富硒碳质岩石出露地段、上坝和下坝地段。在对应的土壤和植物间,硒含量无明显的相关关系,这表明植物对硒的利用并不完全受土壤总硒的影响。30 多年来,坝内土壤硒含量基本无变化,而植物硒含量呈现明显的降低趋势,说明土壤中植物可利用性硒已降低。尽管在流经富硒碳质岩层或废弃的石煤堆旁能够采集到较高的水硒样品,但水硒含量基本无变化的现象说明,在无人为活动的干预下,富硒地段硒的释放已进入了稳定的平衡阶段。渔塘坝硒的分布除与富硒碳质岩石的出露特征、地形特征有关外,还与硒的迁移途径有关。渔塘坝西北部地区出露的富硒碳质岩石仅为高硒区的形成提供了必要条件,而导致坝内高硒土壤形成的主要原因是当地村民的土地耕种方式,如石煤熏土作肥或石煤与石灰的混合来改良土壤等,并进而引起硒在食物链中的富集,且这种影响是长远的。因此,如果当地政府在硒资源的利用和开发上不能够保持合理的规划和使用,渔塘坝仍然是硒中毒可能发生的高风险区,且恩施所有的高硒区也应当是硒中毒的风险区。

Yutangba is one of the most typical high-Se areas in Enshi Prefecture in China. Comprehensive studies were conducted in order to better understand distribution and variation of selenium in soils, plants and water bodies of Yutangba. The results show that high-Se plants and soils are mainly distributed in the northwestern part, Shangba and Xiaba of Yutangba, where exposure of Se-rich carbonaceous strata is found. No significantly positive relationship between soil Se and plant Se was found, which indicates Se uptake by plants is not always controlled by concentration of total Se in the soil. In the past 30 years, selenium content in the soil has remained almost unchanged whereas plant Se has showed a significant declining trend, indicating that in the soil Se available to plants has obviously decreased. Although water samples high in Se can be collected from streams flowing through the Se-rich carbonaceous strata or abandoned stone coal spoils, no obvious variation of Se content in water was observed, demonstrating that the release of Se has reached a geochemical equilibrium. The distribution of Se in Yutangba, apart from topographic and geological factors with regard to Se-rich rocks, is also related to pathways of Se transportation. The exposed Se-rich carbonaceous strata in the northwestern part of Yutangba is a necessary condition for developing high-Se areas, but the high-Se soil in Shangba and Xiaba of Yntangba is attributed to human activities such as cultivation and mining. Local farmers often use Se-rich “stone coals” as fertilizer or soil amendment, thus leading to Se further accumulation in food chain, of which the impact is long term. Therefore should the local government not take adequate measures or make reasonable planning for the exploitation of the Se resources in Enshi Prefecture, the risk of Se poisoning is still very high in Yutangba and some other high-Se places in Enshi Prefecture.