源自腐殖土的溶解性有机质组分对棕壤和黑土吸附苯并三唑的影响

溶解性有机质(DOM)影响着有机污染物在土壤中的吸附行为.将从腐殖土中提取的DOM(DOMbulk)用XAD-8树脂和阴/阳离子交换树脂进行分级,用红外光谱、元素分析、紫外分光光度计和电位滴定的方法对DOM不同组分特征进行分析.用吸附批次实验方法研究了DOM不同组分对棕壤和黑土吸附苯并三唑(BTA)的影响.结果表明,DOMbulk中疏水酸性(HOA)、疏水中性(HON)、亲水酸性(HIA)、亲水碱性(HIB)和亲水中性(HIN)组分比例分别为61%、17%、6%、2%和14%.由于黑土有机碳(OC)含量高于棕壤,黑土对BTA和DOM组分的吸附能力均大于棕壤.相对于黑土,棕壤吸附DOM的标化分配系数Koc较高,其原因是棕壤中含有较多的对吸附DOM起重要作用的黏粒和粉砂.由于水分子占据DOM结合点位,DOM组分与BTA在溶液中结合较弱.DOMbulk中HIN在土壤上吸附最强.HIN的吸附增加了土壤吸附BTA的点位,增加点位的促进吸附作用大于HIN与BTA的竞争吸附作用,最终表现为促进吸附.疏水组分在土壤上的吸附较弱,产生的新吸附点位较少,主要通过竞争吸附作用抑制土壤对BTA的吸附.DOMbulk由78%的疏水组分构成,对土壤吸附BTA的影响与疏水组分相似.

Effects of Dissolved Organic Matter Fractions Extracted from Humus Soil on Sorption of Benzotriazole in Brown Soil and Black Soil

Dissolved organic matter (DOM) affects the sorption behavior of organic pollutants in soils. In this study, bulk DOM (marked as DOM_bulk) was extracted from natural humus soil and divided into five individual fractions by XAD-8 resin and anion/cation exchange resins based on their hydrophobicity-hydrophilicity. The isolated DOM fractions were characterized by FTIR, elemental analysis, UV spectrophotometer and potentiometric titration. Batch experiments were conducted to investigate the effects of different fractions of DOM on sorption of benzotriazole (BTA) in two Chinese reference soils (brown soil and black soil). Proportions of hydrophobic acid (HOA), hydrophobic neutral (HON), hydrophilic acid (HIA), hydrophilic base (HIB) and hydrophilic neutral (HIN) in DOM_bulk were 61%, 17%, 6%, 2% and 14%, respectively. Sorption affinity of BTA and DOM in black soil was greater than that in brown soil, which was attributed to the higher organic carbon (OC) content of black soil as compared to that of brown soil. Brown soil had higher normalized distribution coefficient K_oc of sorbed DOM fractions than black soil, because brown soil has a greater proportion of clay and silt, which play important roles in sorption of DOM fractions. Dialysis-bag experiments demonstrated that binding coefficient between each isolated DOM fraction and BTA in solution was very weak. The reason is that the binding sites of DOM are occupied by water molecules in solution. Among the isolated DOM fractions, HIN showed the strongest sorption affinity in both soils, which increased OC content and consequently produced new sorption sites in soils. The enhanced sorption effect from new sorption sites was greater than that from competitive sorption between BTA and HIN. On a whole, HIN enhanced the sorption of BTA in soil. HOA and HON inhibited the sorption of BTA in soils. Because the sorption of hydrophobic fractions, especially HON, in soils was less than that of other fractions, competitive sorption between hydrophobic fractions and BTA was the main mechanism. DOM_bulk that consists of 78% hydrophobic fractions had similar effects with hydrophobic fractions on sorption of BTA in two soils.