| Kaschin-Beck disease(KBD), an endemic osteoarthropathy, is distributed in the lowselenium(Se)-belt that stretches from northeast to southwest China. However, some regional areas with low soil Se concentration are not always KBD severely afflicted, in fact there is no significant difference in Se levels between KBD villages and control one from the same area. Selenium bio-available concentrations, or the proportions of water-soluble selenium seem more critical in comparison.The present study examined ecological geochemical assessment between KBD-stricken areas in Aba autonomous prefecture of Sichuan Province and Xinghai County in the southern region of Qinghai Province, and ecological healthy area in Ping’an-Ledong of eastern Qinghai Province, focusing on the relationship between the KBD and ecological geochemical environment, the behavior of selenium(Se) and other elements related to KBD, and the influencing mechanism using pedological and geochemical methods, with the purpose of probing further into the ecological constraints of selenium bioavailability and bioaccessibility.The results showed that topsoils in Aba typical area of Sichuan Province occurred Kaschin-Beck disease(KBD) featured high-fluorine(F), low-selenium(Se), and lack of water-soluble selenium. The greatest contributions of soil water-soluble Se in KBD control area were humic bound selenium(Se-humic), followed by selenate with excellent fluidity and solubility, otherwise available phosphorus might promote the bioavailability of Sehumic; while in KBD-stricken area, the biological activity of selenite weakened due to the constraints of soil iron(Fe) oxides / hydroxides and organic matter, where selenite is the main factor to water-soluble selenium. The safety of agricultural products in Aba and Xinghai of KBD typical areas was guaranteed, however low Se levels in crops or the Se enrichment to crops such as highland barley and potatoes were strongly restricted by soil p H, exchangeable calcium(Ex-Ca), exchangeable magnesium(Ex-Mg) and so on. Moreover, the daily intake of iodine(I) and Se of KBD-stricken patients from Aba of Sichuan Province was always lower than the individuals from Ping’an – Xinghai healthy area of Qinghai Province, even was inferior to KBD control area of Aba, and the data of biomarker reflected recent or long-term exposure showed the similarity. The Chemical Index of Alteration(CIA) and the Index of Compositional Variability(ICV) in soil profiles were calculated by 63.05(± 3.54) and 1.17(± 0.14) respectively, indicating local low Se level may be a feature that soils inherit from their Se-deficient parent materials. Rhizosphere soil samples obtained from the study area were classified into Cryic Cambisols(M1), Ustic Isohumisols(J2), Udic Luvisols(L4) and Stagnic Gleysols(I2). The integrated constraints on Se bioavailability in these soils were analyzed, however these soil types showed different geochemical behaviors such as: strong leaching of M1 topsoil with Se(VI), Ca, K, Mg, Al, Fe and Mn reduced elements’ bioavailability; because of precipitation, soluble calcium bicarbonate(Ca(HCO3)2) in topsoil of J2 at hillside carried K, Na, Cl, S, and Se(dissolved elements) away easily, while at valley or depositional districts, partial calcic residues accumulated; the argic horizon in L4 constrained the migration of selenite, Se(IV), and promoted its adsorption on clay and sesquioxide; however, I2 formed in a highland anaerobic environment featured massive amounts of organic matter, lower p H value and peat swamp accumulation with poor drainage, which was one of typical geographical characteristics, abundant humus acid had key influence for Kaschin-Beck disease, despite abundant water-soluble Se to the contrary.These research achievements could provide some foundation of controlling or improving ecological low-Se environment, and developing Se-rich products scientifically, which has a high value of practical application and scientific significance. |
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