病原菌在红壤胶体上的吸附机制研究

研究了pH和KCl离子强度对猪链球菌和大肠杆菌在红壤胶体表面吸附的影响,结合表面物化性质和Derjaguin-Landau-Verwey-Overbeek(DLVO)理论分析互作机制。结果表明,细菌在红壤胶体表面的吸附等温线能较好拟合Freundlich方程(R20.97),猪链球菌在红壤胶体表面吸附的分配系数(Kf)是大肠杆菌的4.5倍～6.1倍,细菌在去有机质胶体表面吸附的Kf值为含有机质胶体的2.4倍～3.2倍。比表面积越大或zeta电位绝对值越小,细菌吸附能力越强,吸附态细菌位于距红壤胶体表面90～100 nm处的次级小能位置。随着体系pH降低(9.0～4.0)或离子强度增大(1～10 mmol L-1),细菌与红壤胶体互作能障降低,细菌吸附量增大,吸附机制符合DLVO理论;而在高离子强度下(50～100 mmol L-1),猪链球菌吸附量降低了3.4%～5.6%,表明除DLVO作用力外,非DLVO作用力如空间位阻排斥和疏水作用对吸附也有贡献。     

流动电位法研究高岭石胶体对包铝石英砂zeta电位的影响

为探讨采用流动电位法表征带电颗粒间相互作用的可行性,采用自制的流动电位测量装置测定了高岭石胶体流经包铝石英砂时zeta电位的变化(Δζ),研究高岭石与包铝石英砂之间的作用程度,考察了包铝程度、介质离子强度和离子种类对带电颗粒之间相互作用的影响。结果表明,可采用流动电位法表征不同尺寸的异电荷颗粒间的相互作用。随着石英砂表面包铝程度的增加和介质离子强度的降低,包铝石英砂的Δζ增加,说明其与高岭石之间的作用程度增加。含低价态离子的溶液中高岭石胶体与包铝石英砂的作用程度大于其在含有高价离子的溶液中。采用经典的DLVO理论计算得到的高岭石胶体与包铝石英砂间的作用能可以很好地解释高岭石对包铝石英砂表面电化学性质的影响,两种异电荷颗粒间的静电引力大小是决定高岭石与包铝石英砂间作用程度的关键因素。在静电力的作用下,高岭石通过电荷屏蔽作用和双电层重叠作用改变包铝石英砂的zeta电位。高岭石与包铝石英砂间的静电引力越大,高岭石对包铝石英砂表面电化学性质的影响越大。     

土壤矿物和胡敏酸对阿特拉津的吸附-解吸作用研究

选取了6种土壤矿物(蒙脱石、高岭石、钙饱和处理蒙脱石、钙饱和处理高岭石、无定型氧化铁和无定型氧化铝),以及从土壤中提取纯化的3种胡敏酸为材料,采用批量吸附平衡法,研究土壤矿物和胡敏酸对阿特拉津的吸附特性。结果表明,各吸附剂对阿特拉津的吸附均能采用Frundlich方程进行较好地拟合(r≥0.982,p0.01)。胡敏酸对阿特拉津具有最大的吸附性能,其固-液分配系数(Kd值)随平衡浓度(Ce值)的变化基本恒定,吸附等温线呈线性(Frundlich方程常数N≈1),吸附以分配溶解作用为主,吸附可逆性较高。黏土矿物(特别是蒙脱石)对阿特拉津也具有较强的吸附能力,Kd值随Ce值增加而增加,吸附等温线呈S型(N1),吸附主要是通过表面亲水作用。无定型氧化铁铝的Kd值随Ce值增加而降低,当Ce达到一定水平后,Kd趋于恒定,吸附等温线呈L形(N1),吸附主要是通过无定型氧化物表面的羟基与阿特拉津分子间的化学键合作用,吸附可逆性最差。     

铁铝氧化物–层状硅酸盐矿物互作对Cr (Ⅵ)和As (Ⅴ)吸附的影响

以高岭石、蒙脱土、针铁矿和三水铝石四种单一典型土壤矿物以及针铁矿-蒙脱石和三水铝石-蒙脱石（质量比为1:1）两种代表性土壤矿物复合体为吸附材料，采用吸附平衡实验、能谱分析（(EDS）、红外光谱、扫描电镜、酸碱滴定和zeta电位测定等方法，研究了铁铝氧化物与层状硅酸盐矿物之间的相互作用对Cr(Ⅵ)和As(Ⅴ)吸附的影响及其机制。吸附平衡实验和EDS实验结果表明，两种复合体对Cr(Ⅵ)和As(Ⅴ)的吸附容量均小于其两种组成矿物单一体系吸附量的平均值，即铁铝氧化物与蒙脱石的互作降低了这些氧化物对Cr(Ⅵ)和As(Ⅴ)的吸附能力。表面性质表征结果表明，与蒙脱石复合后，针铁矿与三水铝石表面的正电荷均被完全中和，电荷符号发生反转。与理论值相比，三水铝石-蒙脱石复合体的表面位点总浓度无明显变化，比表面积减小。针铁矿-蒙脱石复合体的比表面积与理论值无明显差异，但矿物表面位点浓度减小，表面羟基红外吸收峰强度减弱。氧化物与层状硅酸盐矿物互作改变了矿物表面性质，这可能是导致氧化物对Cr(Ⅵ)和As(Ⅴ)的吸附能力降低的主要原因。当评估污染元素在土壤中有效性时应当考虑土壤固相组分间的互作对离子吸附的影响。     

广西水耕人为土黏粒矿物组成及其空间分布特征

黏粒矿物影响着土壤理化性质，可指示成土因素特征和土壤发生发育过程/强度，也是中国土壤系统分类的基层单元土族矿物学类型划分的重要依据。本研究选择了广西不同纬度和成土母质的18个代表性水耕人为土的剖面，应用X射线衍射（XRD）方法分析了其典型水耕氧化还原层（Br层）的黏粒矿物组成及其空间分布特征，并确定了其中“黏质”剖面的土族控制层段矿物学类型。结果表明：（1）供试土壤的黏粒矿物主要包括高岭石、伊利石、三水铝石、1.42 nm过渡矿物、蒙脱石和蛭石等，依次分别出现在100%、88.9%、72.2%、61.1%、44.4%和38.9%的剖面中。（2）黏粒矿物组成在纬度空间分布上具有明显规律性特征。随着纬度降低，土壤黏粒中的高岭石增加，伊利石、蒙脱石、1.42nm过渡矿物逐渐减少；纬度＞23°N区域内，成土母质对黏粒矿物组成影响明显。（3）纬度23°N是黏粒矿物组成和土族矿物学类型分界线，＜23°N区域，黏粒矿物均以高岭石为主，是“黏质”剖面的土族控制层段的主要矿物学类型；＞23°N区域，黏粒矿物组成以高岭石、蒙脱石、伊利石或1.42 nm过渡矿物为主，因成土母质不同而异，“黏质”剖面的土族控制层段矿物学类型包括高岭石混合型、混合型和伊利石型。     

除草剂草甘膦在几种土壤和矿物上的吸附研究

通过批平衡实验考察了草甘膦在几种性质不同土壤和矿物上的吸附行为。研究发现土壤对草甘膦有较强的吸附能力，草甘膦在土壤上吸附量的大小与土壤理化性质密切相关。草甘膦在土壤和矿物上的吸附符合Freundlich吸附方程，其在土壤上的吸附常数K与土壤粘粒含量呈正相关，并随土壤氧化铁和氧化铝含量增加而增加，而与土壤的pH呈显著负相关。草甘膦在高岭石上的吸附量要比在蒙脱石上大，而草甘膦在金属离子饱和的蒙脱石和高岭石上的吸附研究结果表明，草甘膦在钠、钙、铁离子饱和的矿物上的吸附能力依次为Fe-蒙脱石〉Ca-蒙脱石〉Na-蒙脱石和Fe-高岭石〉Ca-高岭石〉Na-高岭石。     

磺胺嘧啶在土壤及土壤组分中的吸附/解吸动力学

抗生素在土壤中的吸附/解吸及迁移过程受其理化性质的强烈影响,其中土壤中的矿物成分,如高岭石、蒙脱石及腐殖酸等是重要控制因素。本文主要研究了磺胺嘧啶在土壤、高岭石、蒙脱石和腐殖酸中的吸附/解吸动力学过程,并对反应前后的高岭石、蒙脱石和腐殖酸进行傅里叶红外光谱(Fourier transform infrared, FTIR)表征,探讨其可能的吸附机理。结果表明:磺胺嘧啶的吸附(解吸)动力学过程,可以分为快速吸附(解吸)、吸附解吸动态平衡和吸附(解吸)平衡3个阶段;磺胺嘧啶在土壤及其3种组分中的吸附(解吸)均可在24 h内达到平衡,其浓度高低会导致土壤及其组分的吸附差异,不同土壤组分中的官能团含量、带电性质及氢键是造成吸附差异的主要原因;分别用伪一级动力学模型、伪二级动力学模型和Elovich模型对其吸附过程进行拟合,其动力学吸附过程更符合伪二级动力学模型,R20.99,主要受控于物理化学吸附;FTIR图谱表明磺胺嘧啶与高岭石以物理吸附为主,并有少量氢键作用,与蒙脱石之间主要以氢键作用完成吸附,而在腐殖酸中存在表面络合和π–π共轭作用。     

不同母质黑钙土黏粒矿物组成研究

以黄土母质和红土母质发育的黑钙土为研究对象,采用化学分析及X射线分析,对同一气候和地理位置条件下的2种母质黑钙土的黏粒矿物组成及其差异进行研究,并探讨其演化机制.结果表明:2种母质黑钙土的黏粒矿物均以2:1型矿物为主,黏粒矿物组成一致性高,均含有蒙脱石、伊利石、蛭石、高岭石和石英.但各层次间衍射峰的强度以及部分衍射峰位置略有变化,红土母质黑钙土底层不存在蒙脱石,表层以绿泥石为主,而黄土母质黑钙土在底层存在绿泥石,在成土中后期可能转化为蛭石.红土母质黑钙土与黄土母质黑钙土相比,高岭石衍射峰强度更强,伊利石强度减弱,且随着土层深度的增加,减弱趋势更为显著,说明红土母质在成土早期,气候湿热,土壤风化较为强烈.     

用悬液Wien效应研究阳离子与土壤粘粒间的能量关系

从能量关系研究土壤带电粘粒与电解质离子间的相互作用一直是土壤化学家希望解决的课题。本文介绍阳离子与带电粘粒间的平均结合自由能和平均吸附自由能的计算公式,并用悬液Wien效应法研究K 、NH4 、Ca2 和Cd2 与黄棕壤、棕壤和黑土粘粒间的能量关系。研究结果表明:K 和NH4 的平均结合自由能范围为6.3~7.1kJmol-1,K 的结合能稍大于NH4 的;Ca2 和Cd2 的结合能范围为7.2~9.4kJmol-1。同一阳离子与不同土壤的结合能顺序如下:黄棕壤<棕壤<黑土。它们在同一高场强(如150kVcm-1)下的平均吸附能ΔGad值:K 和NH4 在黄棕壤和棕壤粘粒上的很接近,分别为0.9和0.8kJmol-1,而在黑土粘粒上,NH4 的较K 的大0.1kJmol-1;Ca2 在黄棕壤和黑土上的吸附能较Cd2 的分别大0.3和0.6kJmol-1;二价阳离子的平均吸附自由能约为一价阳离子的2~2.5倍。     

细菌-矿物互作及其复合体在重金属修复中的应用

利用功能细菌辅助植物固定重金属是目前农田土壤污染修复中高效且环境友好的方式,其中细菌与矿物间相互作用广泛存在,包括细菌对矿物的溶解作用、矿物对细菌活性的影响以及细菌-矿物复合体的形成等,并贯穿整个修复过程。一方面,细菌与矿物互作会影响细菌的活性和表面特性,如带电性、表面官能团位点类型及浓度等,进而影响细菌对重金属的生物吸附行为以及辅助植物修复作用的发挥;另一方面,细菌-矿物结合形成的复合体较单一细菌、矿物组分对重金属的固定行为不同,在重金属修复过程中发挥不可忽视的作用。本文综合分析细菌与矿物的结合作用、细菌对矿物的溶解作用以及矿物对细菌活性的影响,阐述细菌-土壤矿物(矿物材料)复合体在重金属污染修复中的应用潜能,为复合体应用于重金属污染土壤环境提供理论依据。     

Adsorption of DNA on clay minerals and various colloidal particles from an Alfisol

Adsorption and desorption of salmon sperm DNA on four different colloidal fractions from Brown Soil and clay minerals were studied. The adsorption isotherms of DNA on the examined soil colloids and minerals conformed to the Langmuir equation. The amount of DNA adsorbed followed the order: montmorillonite?fine inorganic clay>fine organic clay>kaolinite>coarse inorganic clay>coarse organic clay. A marked decrease in the adsorption of DNA on organic clays and montmorillonite was observed with the increase of pH from 2.0 to 5.0. Negligible DNA was adsorbed by organic clays above pH 5.0. As for inorganic clays and kaolinite, a slow decrease in DNA adsorption was found with increasing pH from 2.0 to 9.0. The results implied that electrostatic interactions played a more important role in DNA adsorption on organic clays and montmorillonite. Magnesium ion was more efficient than sodium ion in promoting DNA adsorption on soil colloids and minerals. DNA molecules on soil colloids and minerals were desorbed by sequential washing with 10 mM Tris, 100 mM NaCl and 100 mM phosphate at pH 7.0. A percentage of 53.7-64.4% of adsorbed DNA on organic clays and montmorillonite was released, while only 10.7-15.2% of DNA on inorganic clays and kaolinite was desorbed by Tris and NaCl. The percent desorption of DNA from inorganic clays, organic clays, montmorillonite and kaolinite by phosphate was 39.7-42.2, 23.6-28.8, 29.7 and 11.4%, respectively. Data from this work indicated that fine clays dominate the amount of DNA adsorption and coarse clays play a more important role in the binding affinity of DNA in soil. Organic matter may not favor DNA adsorption in permanent-charge soil. The information obtained is of fundamental significance for the understanding of the ultimate fate of extracellular DNA in soil.     

低分子量有机配体对黏粒矿物吸附苏云金芽孢杆菌的影响

土壤是微生物的理想栖息地,土壤微生物群落组成复杂,数量巨大。1g土壤中可能栖息着上百亿个微生物,其中细菌可达1010个[1]。约80%～90%的土壤微生物寄居于土壤固相表面,如黏土矿物、金属氧化物或有机质表面[2]。细菌与矿物间的相互作用在土壤污染物转化与降解、团聚体形成[3]、矿物风化[4-6]及病原菌运移[7-8]等诸多过程起着关键作用。     

Sb(V)在三种矿物表面的吸附行为

用研究了蒙脱土、高岭土和针铁矿在不同的pH与离子强度的介质条件下对Sb(V)的吸附及解吸行为。3种矿物对Sb(V)的吸附能力差别较大,蒙脱土的吸附量远大于针铁矿和高岭土,针铁矿与高岭土的吸附能力相近。pH对Sb(V)在3种矿物表面的吸附行为影响显著。随pH的升高,Sb(V)的吸附均减弱。吸附在高岭土表面的Sb(V)易解吸,而针铁矿和蒙脱土表面的Sb(V)不易解吸。随离子强度升高,高岭土对Sb(V)的吸附减弱;离子强度对Sb(V)在针铁矿和蒙脱土表面吸附的影响较小。     

Influences of kaolinite and montmorillonite on benzo[a]pyrene biodegradation by Paracoccus aminovorans HPD-2 and the underlying interface interaction mechanisms

Clay minerals play an important role in biogeochemical cycling. Here, kaolinite and montmorillonite, the two most abundant and widespread clay minerals with typical layered structures, were selected to investigate and compare their effects on the biodegradation of benzo[a]pyrene (BaP) by Paracoccus aminovorans HPD-2 and to investigate the underlying interface mechanisms. Overall, the BaP degradation efficiency was significantly higher 7 d after montmorillonite addition, reaching 68.9% (P < 0.05), when compared with that of the control without addition of clay minerals (CK, 61.4%); however, the addition of kaolinite significantly reduced the BaP degradation efficiency to 45.8%. This suggests that kaolinite inhibits BaP degradation by inhibiting the growth of strain HPD-2, or its strong hydrophobicity and readily agglomerates in the degradation system, resulting in a decrease in the bio-accessibility of BaP to strain HPD-2. Montmorillonite may buffer some unfavorable factors, and cells may be fixed on the surface of montmorillonite colloidal particles across energy barriers. Furthermore, the adsorption of BaP on montmorillonite may be weakened after swelling, reducing the effect on the bio-accessibility of BaP, thus promoting the biodegradation of BaP by strain HPD-2. The experimental results indicate that differential bacterial growth, BaP bio-accessibility, interface interaction, and the buffering effect may explain the differential effects of the different minerals on polycyclic aromatic hydrocarbon biodegradation. These observations improve our understanding of the mechanisms by which clay minerals, organic pollutants, and degrading bacteria interact during the biodegradation process and provide a theoretical basis for increasing the biodegradation of soil pollutants by native microorganisms under field conditions.     

Hydrolysis of cellobiose by β-glucosidase in the presence of soil minerals - Interactions at solid-liquid interfaces and effects on enzyme activity levels

Extracellular enzymatic activities in soils are essential for the cycling of organic matter. These activities take place in multiphase environments where solid phases profoundly affect biocatalytic activities. Aspergillus niger is ubiquitous in soils; its β-glucosidase plays an important role in the degradation of cellulose, and therefore in the global carbon cycle and in the turnover of soil organic matter. However, the information on the interactions of this protein with soil minerals is very limited, and even less is known about their consequences for the hydrolysis of the natural substrate cellobiose. We therefore characterised the sorptive interactions of this enzyme with the soil minerals montmorillonite, kaolinite and goethite and quantified the resulting changes in the hydrolysis rate of cellobiose. Fractions of adsorbed protein, and the resulting catalytic activity loss, were lower for montmorillonite than for kaolinite and goethite at given experimental conditions; adsorption was 9.7 ± 7.3% for montmorillonite, 70.3 ± 3.1% for kaolinite and 71.4 ± 1.8% for goethite, respectively. Adsorption of the protein to the minerals caused a total decrease in the catalytic activity of 18.8 ± 3.4% for kaolinite and 17.9 ± 4.7% for goethite whereas it was not significant for montmorillonite. The average catalytic activity lost by the pool of adsorbed molecules was 26.8% for kaolinite and 25.0% for goethite. Both the amount of adsorbed protein and the resulting loss of catalytic activity were found to be independent of the specific surface areas yet were influenced by the electrical properties of the mineral surfaces. Under the experimental conditions, montmorillonite and kaolinite are negatively charged whereas goethite is positively charged. However, because of the adsorption of phosphate anions from the buffer, a charge reversal took place at the surface of goethite. This was confirmed by zeta (ζ)-potential measurements in phosphate buffer, revealing negative values for all the tested minerals. Indeed goethite interacted with the enzyme as a negatively charged surface: the amount of adsorbed protein and the resulting catalytic activity loss were very similar to those of kaolinite. Our results show that, even if an important fraction of β-glucosidase is adsorbed to the minerals, the catalytic activity is largely retained. We suggest that this strong activity retention in presence of soil minerals results from a selective pressure on A. niger, which benefits from the activity of the adsorbed, and thus stabilized, enzyme pool.     

Interactions of clay minerals with Arthrobacter crystallopoietes: starvation, survival and 2-hydroxypyridine catabolism

For bacterial inoculants to be effective in soil remediation, the bacterial strain must be capable of overcoming any negative effects of soil minerals on cellular processes. One class of minerals commonly encountered by soil bacteria is clays. Thus, the effect of commonly occurring clay minerals in soils on starvation, survival and 2-hydroxypyridine catabolism by Arthrobacter crystallopoietes was evaluated. Stationary phase A. crystallopoietes cells were suspended in 0.03M, pH7.0, phosphate buffer containing no clay or amended with 0.2% (wt/vol) montmorillonite, sodium montmorillonite or kaolinite. Marked effects of clay minerals on both survival rates and catabolic rates of 2-hydroxypyridine were noted. For example, after 14 weeks starvation, 4.6% of the initial cell population was viable with no clay present, compared to 0.8% (montmorillonite), 22.1% (kaolinite) and 54.1% (sodium montmorillonite) in the presence of the clay minerals. Acclimated and nonacclimated cell populations were used to evaluate 2-hydroxypyridine catabolism. Induction of 2-hydroxypyridine metabolism occurred in the unacclimated cells following starvation. Differential impact of the clay minerals on unacclimated cells was detected. Montmorillonite enhanced the capacity for induction of 2-hydroxypyridine catabolism and its decomposition rate after 0–3 days starvation. For acclimated cells, clay did not affect the metabolic activity prior to starvation, but the presence of clay resulted in increased activity during starvation. For example, after 3 days starvation, a nearly two fold increase in metabolism was detected in the presence of clay minerals. These data suggest that some clay minerals in soil alter the survival time and metabolic activity of soil-amended bacteria, thereby affecting the potential for bioremediation success. Received: 1 March 1996     

电解质种类和浓度影响磷酸根解吸的机理研究

本文研究了吸附性阳离子、电解质浓度和组成影响几种矿物和土壤吸附态磷的解吸的机理。结果表明,吸附性阳离子影响磷酸根解吸与离子桥有关。桥接静电场愈强,被束缚磷的释放就愈困难。电解质阳离子对磷酸根解吸的影响则取决于其对表面负电荷的屏蔽效应。阳离子电价高,屏蔽作用大,磷解吸就少。电解质浓度影响吸附态磷的解吸主要与表面电位的变化有关。当pH>PZC值时,提高电解质浓度降低表面负电位,从而减少磷的吸附;当pH<PZC时,提高电解质浓度则降低表面正电位,促进磷的解吸。磷酸根解吸盐效应零点(P_PZSE)值一般都介于土壤或矿物样品吸附磷酸根前后测得的两个PZC值之间。不同浓度电解质溶液中磷解吸量之差与吸附层电位变化量(△ψ_x)呈正相关。     

Adsorption mechanisms of thiazafluron in mineral soil clay components

The adsorption of the herbicide thiazafluron, 1,3-dimethyl-1-(5-trifluoromethyl-1,3,4-thiadiazol-2-yl)urea, by three smectites, illite, kaolinite, ferrihydrite and the clay fraction of an illitic soil (54.9% illite, 17.0% montmorillonite and 24.9% kaolinite) and a montmorillonitic soil (33.9% illite, 55.0% montmorillonite and 11.1% kaolinite) has been determined. Thiazafluron adsorbed on neither kaolinite nor iron oxide. The adsorption isotherms on smectites and illite conformed to the Freundlich equation. Values of K_f-obtained for smectites were larger than for the illite and increased as the layer charge of the smectite decreased. Desorption of thiazafluron on smectites was shown to be highly irreversible. Adsorption isotherms of thiazafluron on different homoionic montmorillonite samples suggest an important role of the exchangeable cations in the adsorption. Infrared spectra and X-ray diffraction analysis of the complexes of thiazafluron with homoionic montmorillonites indicated that thiazafluron adsorbs in the interlamellar space of the smectites, mainly by substitution of water molecules associated with the exchangeable cations through the carbonyl-amide group and formation of H-bonds or waterbridge between the NH group of the amide and the basal oxygens of the montmorillonite. The illitic soil clay adsorbed more of the herbicide than the montmorillonitic one did, suggesting that illite and montmorillonite may be present in soils in altered forms giving rise to different adsorption capacities from those of the pure minerals.     

Surface loading effect on Cd and Zn sorption by kaolinite and montmorillonite from low concentration solutions

Studies of Cd and Zn sorption using Na-saturated kaolinite and montmorillonite, and low metal solution concentrations similar to those found in the environment, showed that metal sorption affinity (measured by K _d values) decreased markedly with increasing surface metal loading for both layer silicates. For equilibrium solution concentrations <0.1 μmol L^?1 for Cd, and < 1 μmol L^?1 for Zn, both metals were sorbed with greater affinity by kaolinite than montmorillonite. These results were probably due to the higher proportion of weakly acidic edge sites present on kaolinite surfaces. In the case of Zn there was an affinity reversal for equilibrium solution concentrations > 1 μmol L^?1, which was attributed to the permanent charge sites of montmorillonite. Cadmium ions were sorbed, by kaolinite, with greater affinity than Zn for equilibrium solution concentrations between 0.3 to 1.5 μmol L^?1. This result was attributed to retention of these metal ions through electrostatic attraction by permanent charge sites present on the kaolinite used in this work. According of these results it seems that metal sorption by these layer silicates involves predominantly edge weak acid sites at lower surface coverages (higher affinity sites), and permanent charge sites at higher metal coverages (lower affinity sites). It was concluded that Cd and Zn sorption by those two layer silicates is greatly influenced by surface metal coverage, and results cannot be extrapolated from low to high surface coverages, and viceversa.     

Sorption of chlorpyrifos to selected minerals and the effect of humic acid

Sorption of chlorpyrifos (CPF) from 2.85 microM (1 mg/L) aqueous solutions in 0.01 M NaCl to montmorillonite, kaolinite, and gibbsite was investigated at 25 degrees C. Uptake of CPF by kaolinite and gibbsite was generally <10%, with pH having at most a small effect. Sorption to montmorillonite was significantly greater, with approximately 50% of the initial CPF being removed from solution below pH 5. Above pH 5 the sorption decreased to about 30%. About 70% of CPF was sorbed to kaolinite and gibbsite after 30 min, whereas on montmorillonite only 50% sorbed in an initial rapid uptake (approximately 30 min) followed by slower sorption, with a maximum achieved by 24 h. Although CPF desorbed completely from kaolinite in methanol, only about two-thirds was desorbed from montmorillonite. CPF has only a weak affinity for the surfaces of kaolinite and gibbsite. In the case of montmorillonite, sorption is significantly stronger and may involve a combination of sorption to external surfaces and diffusion into microporous regions. At pH >6 increased negative surface charge results in a lower affinity of CPF for the external surface. In the presence of 50 mg/L humic acid (HA) the amount of CPF sorbed on gibbsite and kaolinite was 3-4 times greater than that in the binary systems. The HA forms an organic coating on the mineral surface, providing a more hydrophobic environment, leading to enhanced CPF uptake. The HA coating on montmorillonite may reduce access of CPF to microporous regions, with CPF tending to accumulate within the HA coating.