Distribution Of Selenium Species In Greenbelt Soils Of Chengdu And Its Affecting Factors

Selenium is of great significance in environmental and physiological study. The chemical behavior and bioavailability of selenium depend on its speciation in soil. The species of selenium in soils are controlled by physico-chemical properties and other factors in soils. However, there are few researches concerning the distribution of selenium species and its affecting factors based on soil zone and layer depth in urban greenbelt system.The present paper focuses on the contents and distribution of total selenium, selenium species as well as corresponding physico-chemical properties in each soil zone and layer. Besides, the relationships between total selenium, selenium species and physico-chemical parameters were systematically investigated and assessed by calculating Pearson correlation factors. From this paper, it was concluded as follows:(1) A low-cost and wide-linear range procedure was developed for the determination of total selenium and selenium speciation with good accuracy and practicability.(2) Urban greenbelt soil in Chengdu is alkaline while suburb greenbelt soil is acidic; the contents of organic matter and total sulfur in surface are higher than that in sub-surface; the total sulfur contents in surface urban greenbelt soil are close and much higher than that in suburb greenbelt. The average content of organic matter of surface and sub-surface reached maximum in agricultural greenbelt.(3) The maximum means for total selenium in both surface and sub-surface were obtained in agricultural zone. There are significant positive correlations between total selenium and total sulfur in both layers of all greenbelt zones of Chengdu.(4) The proportion of Se species which could be absorbed easily by vegetation (water soluble and exchangeable Se) is highest and very close (40 - 43%) in each urban greenbelt zone. While maximum proportion of residue Se and minimum sum of proportion of water soluble and exchangeable Se were obtained in suburb greenbelt, which is not good for utilization by plants but can efficiently prevent vegetation from over-absorption.(5) In both surface and sub-surface of greenbelt zone of Chengdu, residue Se has a negative relationship with pH and a significant positive correlation with total sulfur; both HCl soluble Se and Se bound to organic matter have a clear positive relationship with total selenium. In sub-surface soils, there is a significant positive correlation between Se bound to organic matter and total sulfur.The conclusion described above is of important significance for study on the mobility and transformation of selenium in urban greenbelt, which is good for environmental evaluation and remediation for selenium contamination.