Determination of available chromium(VI) in paddy soils by using selective ion exchange resin embedded in soils

• Main Authors: Chien-Chung Huang, 黃建中
• Other Authors: Dar-Yuan Lee
• Format: Others
• Language: zh-TW
• Published: 2004
• Online Access: http://ndltd.ncl.edu.tw/handle/81823245943875001787

碩士 === 國立臺灣大學 === 農業化學研究所 === 92 === Chromium in soils is presented in the form of Cr(VI) oxyanions or Cr(III) cation. The toxicity, availability and mobility of Cr(VI) is higher than those of Cr(III), thus it is worth to evaluate the Cr(VI) availability of soils. Since soil redox potential can influence the distribution of Cr between Cr(VI) and Cr(III) forms, an in situ method that will not affected by the change of soil properties due to soil preparation needs to be developed for determining Cr(VI) availability in paddy fields. In this study, a selective ion exchange resin (DOWEX M4195) was used to test its feasibility for determining Cr(VI) availability by embedding the resin in paddy soils. The amounts of soil Cr(VI) extracted by the resin were correlated with growth and Cr uptake of rice seedlings grown on the studied Cr(VI)-added soils. Three Taiwan representative agriculture soils [Pingchung (Pc)、Chringchung (Cf) and Taikang (Tk)] were used in this study. Three studied soils were added with K2CrO7 solutions to reach the level of 0、75、175、200、250、300 mg Cr/kg soil respectively. One gram of Cu-saturated selective ion exchange resin was horizontally embedded in saturated soil pastes and recovered after various time ( 1、2、3、4 days) intervals, and the amounts of Cr(VI) adsorbed on the ion exchange resin were measured in order to determine the time needed for equilibrium. The results showed that the amounts of Cr(VI) accumulated on the ion exchange resin increased as the length of embedded time increased, and reached a nearly constant value after 2 days. Among the three studied soils at the same level of Cr(VI) addition, the amounts of Cr(VI) in soils extracted by selective ion exchange resin method are in the order of Tk-soil＞Cf-soil＞Pc-soil. In addition, the studied soils were pre-flooded for 7、15、30 days respectively before the ion exchange resin was embedded in saturated soils and recovered after 2 days. The amounts of Cr(VI) adsorbed on the ion exchange resin were measured to determine the contents of soil available Cr(VI) are affected by pre-flooding time in paddy soils. The results showed that the amounts of soil Cr(VI) extracted by the ion exchange resin decreased as the pre-flooding time (7 to 30 days) increased. The amounts of soil Cr(VI) extracted by the resin were correlated with growth and Cr uptake of rice seedlings grown on the studied Cr(VI)-added soils. Three studied soils were pre-flooded for 7 days and used to grow rice seedlings in the phytotron. The growth of rice seedlings were investigated. The results showed that the growth of rice seedlings were found to be inhibited by the added Cr(VI). The extent of inhibition increased with the amounts of Cr(VI) added to soils. Among the three studied soils, the growth of rice seedlings in the Tk-soil and Cf-soil were much inhibited by Cr than that in the Pc-soil. The amounts of soil extractable Cr(VI) by ion exchange resin had significantly positive correlation with the toxic effect of rice seedlings are affected by Cr. The above results indicated that the ion exchange resin embedded method is suitable for determining Cr(VI) availability of paddy soils across a wide range of properties. In addition, the method may be feasible for in situ determining the Cr(VI) availability of paddy soils.