江苏宜溧富硒稻米产区地质地球化学背景

江苏宜溧地区分布有400 km2多的富硒土壤,并产出天然富硒稻米。通过系统分析研究宜溧富硒稻米产地的稻米、土壤、岩石、水样的Se等元素地球化学数据,探讨了控制宜溧地区富硒稻米产出的主要地质环境及地球化学背景因素,总结了Se等元素在米-土-岩之间的分布迁移特征。结果显示:(1)宜溧地区产出的富硒稻米主要受富硒耕地控制,稻米Se与耕地土壤Se、Corg.之间存在显著正相关性,米Se与土Se的相关系数R=0.81,土壤Se≥0.5 mg/kg的耕地中富硒稻米检出率为100%;(2)二叠系煤系地层中的杂色泥质粉砂岩、页岩是主要富硒原岩,其平均Se含量达到17.22 mg/kg,比当地土壤中Se高出5倍以上。富硒原岩沉积厚度越大,其上覆土壤的Se含量越高;(3)上述富硒岩层中夹杂一层几到几十厘米厚的铁锰结核透镜状沉积物,富集Fe、Mn、Cd、S、P等,其风化形成土壤可能富集Cd,但富硒稻米中未检测到Cd超标;(4)耕地土壤中有效Se小于0.02 mg/kg,有效Se占土壤Se的比例为0.16%~2%。富硒耕地土壤总体偏酸性,其p H一般介于4.6~6.5,富硒原岩更偏酸性,其p H一般介于4.2~5.5;(5)Se从源头向耕地迁移也是一个不断均匀化的过程,地势、气候条件、断层等对富硒耕地的分布有影响,山间盆地、沟谷、山前平原是形成天然富硒耕地的主要场所,特定断层可成为天然富硒耕地的边界。

Geological and geochemical background of Se-rich rice production in Yili area, Jiangsu Province

There exist abundant Se-rich soil resources over 400 km² in the Yili area, Jiangsu Province, and a part of natural Se-rich rice has been produced in this area. By systematically studying and analyzing newly-obtained elemental geochemical data from the typical samples about rice seeds, soil, rock and soil solution related to Se-rich rice origin, this paper discusses the main controlling factors and geological environment or geochemical background for producing the natural Se-rich rice in the Yili area, and summarizes distribution and migration characteristics of some trace elements such as Se within rice as well as soil and rock. Some conclusions have been reached:(1) Se concentration in rice is significantly correlated to Se and TOC in soil, with the correlation coefficient (R) being 0.81. Detection rate of Se-rich rice is 100% when Se concentration is more than 0.5 mg/kg in soil; (2) Permian coal-bearing strata seem to be main primitive sources to form Se-rich soil, and the variegated argillaceous siltstone and shale within the strata are important Se-rich rocks, and the average Se concentration is 17.22 mg/kg in these rocks, which is more than 5 times higher than the average Se concentration in the local soil; and there are some obvious positive correlation between rock thickness and Se concentration in its overlying soil:where the sedimentary thickness of the Se-rich rock increases, the Se concentration is higher in the overlying soil layer; (3) The above-mentioned Se-rich rock formation includes a layer of iron and manganese nodule sediments lenticular in form, its thickness is about 5-30 cm, and there are abundant Fe, Mn, Cd, S, P and some other elements in the nodule sediments; the weathering and transferring process to form soil may contain a part of Cd, but the Cd that exceeds the value of the standard sample has not been yet detected in those relevant Se-rich rice seeds; (4) the available Se concentration is lower than 0.02 mg/kg in the cultivated soil, and the ratio of the available Se concentration to Se concentration is from 0.16% to 2% or so in the cultivated soil; and the most cultivated soils that enrich selenium are acidic, their pH values are between 4.6 and 6.5; the original Se-rich rocks are more acidic, with their pH values being generally between 4.2 and 5.5; (5) Se migration process is a series of continuous dilutions or homogeneous movements. Se-rich farmland distribution is influenced by the terrain, rainfall, fault belt and some other factors. The natural Se-rich farmland is formed in the small basin in hills, valley and piedmont plain with fault belts becoming the natural boundary of Se-rich farmland.