Selenium Speciation Of Se-rich Carbonaceous Rocks From Yutangba, Enshi, Hubei Province, China

In the environment, the mobilization, transformation, bioavailability and toxicity of selenium are mostly being controlled by its chemical speciation. Yutangba, Enshi, Hubei province, China is the only site in the world where a sudden incidence of human selenosis took place, and one of the typical Se-rich areas in China. The Se-rich carbonaceous rocks in the north of Yutangba is prevalently being recognized as the main source of selenium of Yutangba. But there has no systematical report on the fractionation and speciation of the Se-rich carbonaceous rocks and Se-rich soils of Yutangba. Here we use a seven operationally defined chemical sequential-extraction procedure followed by speciation treatments and quantitative analysis by Hydride Generation-Atomic Fluorescence Spectroscopy, to study the Se-rich carbonaceous rocks and soils of Yutangba, Enshi, Hubei province. The major findings are listed as follows:1. As for Se-rich carbonaceous rocks and Se-rich soils, we use a seven operationally defined chemical sequential-extraction procedure, which including: Water soluble Se, ligand exchangeable Se, organic bound Se, elemental Se , carbonates associated Se, sulfide/selenide associated Se, residue Se. The recovery of the scheme is 85.1~114.5%,with an average recovery of 98.8%. The average coefficient of variation(CV) between replicates<10%. Sum of the seven fractions Se are significantly correlated with the total Se value which was independently determined by mixed acid digestion on separate samples (correlation coefficient>0.99) .All of these indicate that the sequential-extraction scheme used in this study is feasible.2. In the Se-rich carbonaceous shale and carbonaceous siliceous rock samples, according to the average proportion values, the Se fractions are: organic bound Se(59.1%) > sulfide/selenide associated Se(13. 1%) > ligand exchangeable Se(11.0%) > water soluble Se(9. 5%) > elemental Se(3. 3%) > residue Se(1.9%) > carbonates associated Se(0.2%). In the Se-rich mudstones and soils, things are a little different, according to the average proportion values, organic bound Se(41. l%) or elemental Se(41.8%)...