Yang Yaning, Sheng Guangyao
Department of Crop, Soil, and Environmental Sciences, University of Arkansas, Fayetteville, Arkansas 72701, USA.
Environ Sci Technol. 2003 Aug 15;37(16):3635-9. doi: 10.1021/es034006a.
Lack of proper techniques to isolate black carbon (BC) from soils has hindered the understanding of their roles in the sorption and environmental fate of organic contaminants in soils and sediments. The burning of crop residues may be the primary source of BC in agricultural soils. In this study, wheat (Triticum aestivum L.) and rice (Oryza sativa L.) residues were burned, and the resulting particulate matter (ashes) along with a soil were used to sorb diuron from water. Calculations indicated that the burning of crop residues may result in an appreciable level of ashes in soils. The diuron sorption isotherms on ashes were curvilinear Langmuir type, suggestive of surface adsorption and similar to that with activated carbon. Ashes were 400-2500 times more effective than soil in sorbing diuron over the concentration range of 0-6 mg/L. Sorption by wheat ash-amended soils and the degree of isotherm nonlinearity increased with increasing ash content from 0% to 1% (weight), indicating the significant contribution of wheat ash to the sorption. Calculations show that wheat ash and soil independently contributed to the sorption. Above the wheat ash content of 0.05%, the sorption was largely controlled by the ash. Density-based fractionation and repeated HCI-HF washing of wheat ash yielded carbon-enriched fractions and enhanced diuron sorption by these fractions. BC appeared primarily responsible for the high adsorptivity of ashes. Ashes arising from the burning of crop residues may be an important determinant of pesticide immobilization and environmental fate in soils.
缺乏从土壤中分离黑碳（BC）的适当技术阻碍了人们对其在土壤和沉积物中有机污染物吸附及环境归宿方面作用的理解。作物秸秆燃烧可能是农业土壤中黑碳的主要来源。在本研究中，燃烧了小麦（Triticum aestivum L.）和水稻（Oryza sativa L.）秸秆，将产生的颗粒物（灰烬）与一种土壤用于从水中吸附敌草隆。计算表明，作物秸秆燃烧可能导致土壤中产生相当数量的灰烬。敌草隆在灰烬上的吸附等温线为曲线型朗缪尔等温线，表明是表面吸附，且与活性炭的吸附等温线相似。在0 - 6 mg/L的浓度范围内，灰烬对敌草隆的吸附效果比土壤高400 - 2500倍。小麦灰烬改良土壤的吸附以及等温线非线性程度随灰烬含量从0%增加到1%（重量）而增加，表明小麦灰烬对吸附有显著贡献。计算表明，小麦灰烬和土壤对吸附的贡献是独立的。当小麦灰烬含量高于0.05%时，吸附主要由灰烬控制。基于密度的分级分离以及对小麦灰烬进行重复的盐酸 - 氢氟酸洗涤得到了富含碳的级分，且这些级分对敌草隆的吸附增强。黑碳似乎是灰烬具有高吸附性的主要原因。作物秸秆燃烧产生的灰烬可能是土壤中农药固定和环境归宿的重要决定因素。
