Studies on the sorption and desorption characteristics of Zn(II) on the surface soils of nuclear power plant sites in India using a radiotracer technique

Zinc adsorption was studied in the soils of three nuclear power plant sites of India. 65Zn was used as a radiotracer to study the sorption characteristics of Zn(II). The sorption of zinc was determined at 25 and 45 degrees C at pH 7.8+/-0.2 in the solution of 0.01 M Ca(NO3)2 as supporting electrolyte. The sorption data was tested both in Freundlich and Langmuir isotherms and could be described satisfactorily. The effect of organic matter and other physico-chemical properties on the uptake of zinc was also studied in all the soil samples. The results showed that the cation exchange capacity, organic matter, pH and clay content were the main contributors to zinc sorption in these soils. The adsorption maximum was found to be higher in the soil on Kakarpara Atomic Power Plant sites soils having high organic matter and clay content. The zinc supply parameters of the soils are also discussed. In the desorption studies, the sequential extraction of the adsorbed zinc from soils showed that the diethylene triamine penta acetic acid extracted maximum amount of adsorbed zinc than CaCl2 and Mg(NO3)2. The zinc sorption on the soil and amount of zinc retention after extractants desorption shows a positively correlation with vermiculite and smectite mineral content present in the clay fraction of the soil. The amount desorbed by strong base (NaOH) and demineralised water was almost negligible from soils of all the sites, whereas the desorption by strong acid (HNO3) was 75-96% of the adsorbed zinc.     

Sorptive behavior of the phenylamide fungicides,mefenoxam and metalaxyl,and their acid metabolite in typical Cameroonian and German soils

Laboratory soil sorption experiments were conducted on mefenoxam, formulated metalaxyl (F-metalaxyl), pure metalaxyl (P-metalaxyl) and metalaxyl acid metabolite to elucidate differences in their sorptive behaviour on typical Cameroonian forest soil (sand clay loam, pH 4.8 and 3.01% OC) and German soil (sandy loam, pH 7.2, 1.69% OC) using a batch equilibrium method. The data obtained on all test chemicals conformed to linear and Freundlich adsorption isotherms. The Langmuir equation failed to describe the sorption of the substances tested. All substances were adsorbed to a greater extent by the Cameroonian soil. The average percentage adsorptions for mefenoxam, F-metalaxyl, P-metalaxyl and the acid metabolite on the Cameroonian soil were 27.8%, 28.3%, 31.8% and 46.8% respectively while for the German soil they were 21.7%, 21.5%, 24.7% and 9.8% respectively. The KD and KF parameters and the Freundlich exponential term (1/n) were low, indicating that the interactions between soil particles and the fungicides were weak. The sorption parameters were lower in the German soil. P-metalaxyl exhibited a higher adsorption capacity than F-metalaxyl in both soils. Mefenoxam and F-metalaxyl exhibited similar sorption parameters in soils, whereas those of P-metalaxyl and acid metabolite differed. Differences observed in the adsorption between the two soils could be attributed to their properties. Desorption studies revealed that the adsorbed fungicides were not firmly retained by soil particles and their adsorption was reversible. Desorption of adsorbed mefenoxam, P-metalaxyl and of the acid metabolite from German soil was almost completely reversible with percentage desorption rates of more than 91.0%, whereas the rate for F-metalaxyl was 74.1%. All compounds exhibited some resistance to desorption from the Cameroonian soil, with percentage desorption rates less than 77.0%. Therefore if degradation in the soil is slow the fungicides described have a potential to leach to lower soil horizons.     

Photoinductive properties of soil humic acids and their fractions obtained by tandem size exclusion chromatography-polyacrylamide gel electrophoresis.

Humic acids (HAs) from three soils of different origin (Chernozem, Ferralsol and Ranker) have been fractionated by coupling size exclusion chromatography (SEC) and polyacrylamide gel electrophoresis (PAGE) on three fractions (fractions A, B, C + D) with different molecular sizes (MSs) and exactly defined electrophoretic mobility (EM). Fractions identically marked had similar EM and MS, independently of HA sources. The photoinductive properties of the whole HAs and their fractions were compared by studying the photoinduced transformation of fenuron at 365 nm. High MS fractions A and B appeared to exhibit poor photoinductive activities compared to the whole HAs, whereas low MS fraction C + D in Chernozem and Ranker were more efficient than the whole HAs. A fourth intermediary fraction containing a mixture of fractions B and C + D with small amount of D was shown to photoinduce poorly the transformation of fenuron. It was therefore concluded that the molecules capable of photoinducing the transformation of fenuron were mainly contained in fraction D. Fluorescence properties of Chernozem HA and its fractions have been tested. Fraction C + D exhibited a very similar fluorescence emission spectrum in comparison with the whole HA and in contrast, the fractions A and B emitted very weakly.     

Cadmium adsorption and desorption behaviour on goethite at low equilibrium concentrations: effects of pH and index cations

The transport and bioavailability of cadmium is governed mainly by its adsorption-desorption reactions with minerals such as goethite--a common iron oxide mineral in variable charged and highly weathered tropical soils. Soil factors such as pH, temperature, solution Cd concentration, ionic strength and ageing affect Cd adsorption on goethite. The desorption behaviour of Cd from goethite at low concentrations is not fully understood. This study investigates the adsorption-desorption of Cd at low Cd concentrations (Cd adsorbed on goethite from 20 to 300 microM Cd solutions) in Na and Ca nitrate solutions of 0.03 M nominal ionic strengths. Synthetic goethite prepared by ageing a ferric hydroxide gel at high pH and room temperature was used for Cd adsorption and desorption studies. For desorption experiment 10 successive desorptions were made for the whole range of initial Cd concentrations (20-300 microM) in the presence of 0.01 M Ca(NO3)2 or 0.03 M NaNO3 solutions. Cadmium adsorption was found to be higher in Na+ than Ca2+ probably due to the competition of Ca2+ ions with Cd2+ ions for adsorption sites on the surfaces of goethite. The effect of index cation on Cd adsorption diminished with increase in pH from 5.0 to 6.0. Cadmium desorption decreased with increase in pH from 5.0 to 6.0 in both Na and Ca systems. After 10 successive desorptions with 0.03 M NaNO3 at the lowest initially adsorbed Cd approximately 45%, 20% and 7% of the adsorbed Cd was desorbed at pH 5.0, 5.5 and 6.0, respectively. The corresponding desorptions in the presence of 0.01 M Ca(NO3)2 were 49%, 22% and 8%, respectively. The Freundlich parameter, k, based on each progressive step of desorption at different adsorbed concentration increased with increasing desorption step, which may indicates that a fraction of Cd was resistant to desorption. Low Cd desorbability from goethite may be due to its specific adsorption and/or possibly as a result of Cd entrapment in the cracks or defects in goethite structure.     

Zinc, copper and nickel concentrations in soil extracts and crops grown on four soils treated with metalloaded sewage sludges

Sludges containing high concentrations of zinc, copper or nickel and an uncontaminated sludge were added to two sandy loams (pH 6.5 and 7.1), a heavy clay (pH 6.3) and a calcareous clay (pH 7.8) to give ten sludge treatments for each soil. The mixtures were incubated fallow, cropped continuously with clover, or cropped with barley and red beet in rotation for 21 months. The quantity of added metal either in the soil solution or extracted by 0.1m CaCl(2) depended on the metal loading, pH and soil cation exchange capacity, and changed with time after mixing soils and sludges. Crop metal concentrations, and the occurrence of metal-induced yield reductions, also depended on soil properties as well as metal loading. The best chemical extractant for predicting plant metal concentrations was 0.1m CaCl(2).     

Factors influencing lead sorption-desorption at variable added metal concentrations in Rhodoxeralfs

The response of ten soils of the lithic Rhodoxeralf type to the supply of lead at concentrations of 500, 1000, 2000, 3000, 4000, 5000 and 6000 mg kg-1 was examined in batch sorption-desorption tests. Lead availability in the soils was found to depend on its partitioning between the soil solution and the solid phase as reflected in adsorption isotherms. The isotherms, of the H type, were consistent with a high affinity of the sorbent for the metal, with which it forms stable inner-sphere complexes on the soil surface. Sorption-desorption tests revealed that some properties of the soils such as their pH (mean=8) and high contents in clays (particularly in kaolinite) and crystalline iron oxides significantly influence Pb sorption, the effect being especially marked at high added metal concentrations. Added lead is largely retained by crystalline iron oxides and the soil clay fraction; the pH of the soil favours the release of variably-charged sites from both. The extent of Pb desorption was small, particularly at the lowest added levels (500 and 1000 mg kg-1). Desorption increased with increasing added Pb concentration and exceeded 50% at 5000 and 6000 mg kg-1; this suggests that Pb is present not only as inner-sphere complexes, but also as outer-sphere complexes and, partly, as precipitates. The desorption isotherms consist of three segments that exhibit significant differences depending on the added Pb concentration, namely: 500-1000, 2000-4000 and 5000-6000 mg kg-1.     

Effects of pH, organic acids, and competitive cations on mercury desorption in soils

The effects of pH, organic acids, and competitive cations on Hg(2+) desorption were studied. Three representative soils for rice production in China, locally referred to as a yellowish red soil (YRS), purplish clayey soil (PCS), and silty loam soil (SLS) and classified as Gleyi-Stagnic Anthrosols in FAO/UNESCO nomenclature, were, respectively, collected from Jiaxin County, Deqing County, and Xiasha District of Hangzhou City, Zhejiang Province. Most of the added Hg(2+) was adsorbed at low initial concentrations (<2 mg l(-1)). Desorption of the adsorbed Hg(2+) in 0.01M KCl (simulating soil solution) was minimal, but was significantly enhanced by the change of pH, and the presence of organic acids or competitive cations. The desorption of Hg(2+) in the soils decreased with pH from 3.0 to 5.0, leveled off at pH 5.0-8.0, but increased with pH from 7.0 to 9.0. The presence of organic ligands enhanced Hg(2+) desorption in the soils except for YRS, in which the addition of tartaric, malic, or oxalic acid reduced Hg(2+) desorption at low concentrations (<10(-4)M), but Hg(2+) desorption generally increased with organic acid concentration. Citric acid was most effective in increasing Hg(2+) desorption, followed by tartaric acid and malic acid; and oxalic acid was the least effective. Desorption of adsorbed Hg(2+) increased with increasing concentrations of added Cu(2+) or Zn(2+). Applied Cu(2+) increased Hg(2+) desorption more than Zn(2+) at the same loading rate. CAPSULE: The effects of organic acids and competitive cations on Hg desorption in soil-water system are related to their concentrations, basic chemical properties, and soil properties.     

Sorption and mobility of metronidazole, olaquindox, oxytetracycline and tylosin in soil

Laboratory studies were conducted to characterise four different antibiotic compounds with regard to sorption and mobility in various soil types. Distribution coefficients (Kd values) determined by a batch equilibrium method varied between 0.5 and 0.7 for metronidazole, 0.7 and 1.7 for olaquindox and 8 and 128 for tylosin. Tylosin sorption seems to correlate positively with the soil clay content. No other significant interactions between soil characteristics and sorption were observed. Oxytetracycline was particularly strongly sorbed in all soils investigated, with Kd values between 417 in sand soil and 1026 in sandy loam, and no significant desorption was observed. Soil column leaching experiments indicated large differences in the mobility of the four antibiotic substances, corresponding to their respective sorption capabilities. For the weakly adsorbed substances metronidazole and olaquindox the total amounts added were recovered in the leachate of both sandy loam and sand soils. For the strongly adsorbed oxytetracyline and tylosin nothing was detected in the leachate of any of the soil types, indicating a much lower mobility. Results from defractionation and extraction of the columns (30 cm length) showed that 60-80% of the tylosin added had been leached to a depth of 5 cm in the sandy loam soil and 25 cm in the sand soil.     

Effect of farmyard manure application on boron adsorption-desorption characteristics of some soils

Boron (B) availability to crop plants depends on soil properties as well as management practices like liming, fertilization and use of organic manures. To assess the effect of farmyard manure (FYM) application on availability of added B, adsorption-desorption of B was investigated in five different soils receiving varying doses of FYM (0, 5 and 10 g FYM kg(-1) soil). Two surfaces Freundlich model was found best to account for B adsorption-desorption data of all soils. Application of FYM increased B adsorption capacities pertaining to low (K1) and high (K2) concentration ranges in all soils, except Soil C (Alfisol) having a pH of 9.8, in which the higher rate of FYM decreased the value of K2. Application of FYM did not change B desorption capacities of soils corresponding to low B concentration range (K(1)(1)) significantly, however, it increased B desorption capacity pertaining to high B concentration (K(1)(2)) in all soils, except Soils C (Alfisol) and E (Entisol) having pH of 9.8 and 5.1, respectively. Application of FYM increased the desorption slope factor applicable to low concentration range (1/n(1)(1)) in Soil A (Inceptisol), but decreased it in Soil E (Entisol). The 1/n(1)(2) (desorption slope factor applicable to high concentration range) decreased with FYM application in all soils except Soil E (Entisol), where it was increased. Boron desorption index (slope(ads)/slope(des)) decreased with FYM application in low B concentration range, but increased in high concentration range for all soils except soil E (Entisol, pH 5.1), in which a reverse trend was observed. Application of FYM increased the retention of added B in soils and may help reducing the leaching losses.     

Irrigation of soil with synthetic landfill leachate--speciation and distribution of selected pollutants

The fates and toxicities of selected landfill leachate pollutants in a soil with a low attenuation potential were investigated. Soil columns consisting of a loamy sand which had been irrigated with synthetic landfill leachates were dissected and analysed for pH, electrical conductivity, copper and zinc species, iron and phenol concentrations and microbial activity. Copper was found to be least mobile and accumulated in the top 4 cm of the soil columns. Sequential extraction of the soil revealed that at least two-thirds of the total copper was in the EDTA-, NaOH-extractable and residual fractions. Approximately 2% of the copper was water soluble and between 1 and 22% was in the MgCl(2)-extractable fraction. Zinc and phenol were relatively mobile and were detected throughout the soil-column profile as well as in the column effluents. The greatest zinc fraction (55-71%) was MgCl(2)-extractable. Zinc solubility in water was again low (1-4%). Phenol was partially adsorbed by the soil but its main attenuation occurred by biodegradation. Microbial activity was affected by the availability of the carbon source as well as the presence of copper and zinc. Copper was more inhibitory to microbial activity than zinc. In the presence of phenol, the simultaneous application of zinc and copper distinctly reduced microbial activity. No inhibitory effect of copper and zinc was observed in the absence of phenol when the microorganisms were severely carbon limited.     

Adsorption and desorption characteristics of hydrophobic pesticide endosulfan in four Indian soils

Adsorption and desorption characteristics of endosulfan in four Indian soils were studied extensively. The soils used were clayey soil (CL--lean clay with sand), red soil (GM--silty gravel with sand), sandy soil (SM--silty sand with gravel) and composted soil (PT--peat) as per ASTM (American Society for Testing and Materials) standards. Adsorption and desorption rates were calculated from kinetic studies. These values varied for alpha and beta endosulfan depending on the soil type. Maximum specific adsorption capacities (qmax) for different soils were calculated by Langmuir model. The values varied from 0.1 to 0.45 mg g(-1) for alpha endosulfan and 0.0942-0.2722 mg g(-1) for beta endosulfan. Maximum adsorption took place in clay soil followed by composted soil and red soil. Adsorptions of alpha and beta endosulfan were negligible in sand. The binding characteristics of various functional groups were calculated using Scatchard plot. Effect of functional groups was more predominant in clayey soil. Organic matter also played a significant role in adsorption and desorption of endosulfan. Endosulfan adsorption decreased drastically in clay soil when the pH was reduced. Desorption was higher at both acidic and alkaline pH ranges compared to neutral pH. Results indicated that alpha endosulfan is more mobile compared to beta endosulfan and mobility of endosulfan is maximum in sandy soil followed by red soil. It can be inferred that crystal lattice of the clay soil plays a significant role in endosulfan adsorption and desorption. Immobilization of endosulfan is more advisable in clay soil whereas biological and or chemical process can be applied effectively for the remediation of other soil types.     

Carbendazim sorption-desorption in Vietnamese soils

Four Vietnamese soils (denoted AG, CT, ST and TG) which differed with respect to pH (pH 2.9-5.4), clay (17-50%) and organic matter (0.3-9.8%) content, were selected for sorption and desorption studies of carbendazim using the batch equilibration technique. Sorption increased with increasing organic carbon (OC) and clay content. Kd values for carbendazim sorption on AG, CT, ST, TG soils at initial concentration of 20 microg/g were 12.5, 127, 8.1 and 9.6 ml/g, respectively. The OC partition coefficients (Koc) for AG, CT, ST and TG were 1140, 1300, 2700 and 960 ml/g, respectively. Carbendazim was strongly sorbed and the binding was less reversible in the acid sulfate soil (CT), than in the other soils. The CT soil had both the highest OC content (9.8%) and the highest clay content (49.8%). The influence of pH on carbendazim sorption was studied in the ST and CT soils. Sorption of carbendazim by the sandy ST soil (OC 0.3%; clay content 26.3%) increased as the pH decreased, while sorption of carbendazim by the CT soil decreased as pH decreased.     

Sorption and leaching of flucetosulfuron in soil

Abstract

The adsorption–desorption and leaching of flucetosulfuron, a sulfonylurea herbicide, was investigated in three Indian soils. Freundlich adsorption isotherm described the sorption mechanism of herbicide with adsorption coefficients (K_f) ranging from 17.13 to 27.99 and followed the order: Clayey loam?>?Loam?>?Sandy loam. The K_f showed positive correlation with organic carbon (OC) (r?=?0.910) and clay content (r?=?0.746); but, negative correlation with soil pH (r = ?0.635). The adsorption isotherms were S-type suggesting that herbicide adsorption was concentration dependent and increased with increase in concentration. Desorption followed the sequence: sandy loam?>?clayey loam?>?loam . Hysteresis (H) was observed in all the three soils with H?<?1. Leaching of flucetosulfuron correlated positively with the soil pH; but, negatively with the OC content. Sandy loam soil (OC- 0.40%, pH ?7.25) registered lowest adsorption and highest leaching of flucetosulfuron while lowest leaching was found in the loam soil (pH ? 7.89, OC ? 0.65%). The leaching losses of herbicide increased with increase in the rainfall intensity. This study suggested that the soil OC content, pH and clay content played important roles in deciding the adsorption–desorption and leaching behavior of flucetosulfuron in soils.     

Desorption of cadmium from goethite: effects of pH, temperature and aging

Cadmium is perhaps environmentally the most significant heavy metal in soils. Bioavailability, remobilization and fate of Cd entering in soils are usually controlled by adsorption-desorption reactions on Fe oxides. Adsorption of Cd on soil colloids including Fe oxides has been extensively studied but Cd desorption from such soil minerals has received relatively little attention. Some factors that affect Cd adsorption on goethite include pH, temperature, aging, type of index cations, Cd concentrations, solution ionic strength and presence of organic and inorganic ions. This research was conducted to study the influence of pH, temperature and aging on Cd desorption from goethite. Batch experiments were conducted to evaluate Cd desorption from goethite with 0.01 M Ca(NO3)2. In these experiments Cd desorption was observed at 20, 40 and 70 degrees C in combination with aging for 16 h, 30, 90 and 180 d from goethite that adsorbed Cd from solutions containing initial Cd concentrations of 20, 80 and 180 microM. Following the adsorption step Cd desorption was measured by 15 successive desorptions after aging at various temperatures. At the lowest amount of initially adsorbed Cd and equilibrium pH 5.5, cumulative Cd desorption decreased from 71% to 17% with aging from 16 h to 180 d and the corresponding decrease at equilibrium pH 6.0 was from 32% to 3%. There was a substantial decrease in Cd desorption with increasing equilibration temperature. For example, in goethite with the lowest amount of initial adsorption at equilibrium pH 5.5, cumulative Cd desorption decreased from 71% to 31% with increase in temperature from 20 to 70 degrees C, even after 16 h. Dissolution of Cd adsorbed goethite in 1M HCl, after 15 successive desorptions with 0.01 M Ca(NO3)2, indicated that approximately 60% of the Cd was surface adsorbed. Overall, dissolution kinetics data revealed that 23% to 88% Cd could not be desorbed, which could possibly be diffused into the cracks and got entrapped in goethite crystals. At elevated temperature increased equilibrium solution pH favoured the formation of CaCO3 and CdCO3 which reasonably decreased Cd desorption. Cadmium speciation showed the formation of calcite and otavite minerals at 40 and 70 degrees C due to increase in pH (>9.5) during aging. X-ray diffraction analysis (XRD) of these samples also revealed the formation of CaCO3 at elevated temperatures with aging. While mechanisms such as Cd diffusion and/or entrapment into fissures and cracks in goethite structure with increase in temperature and aging are possible.     

Adsorption-desorption and leaching of pyraclostrobin in Indian soils

Pyraclostrobin is a new broad-spectrum foliar applied and seed protectant fungicide of the strobilurin group. In this paper, adsorption-desorption of pyraclostrobin has been investigated in three different soils viz. Inceptisol (sandy loam, Delhi), Vertisol (sandy clay, Hyderabad) and Ultisol (sandy clay loam, Thrissur). Effect of organic matter and clay content on sorption was also studied in Inceptisol of Delhi. Leaching potential of pyraclostrobin as influenced by rainfall was studied in intact soil columns to confirm the results of adsorption-desorption studies. The adsorption studies were carried out at initial concentrations of 0.05, 0.1, 0.5, 1 and 1.5 μg mL^?1. The distribution coefficient (K_d) values in three test soils ranged from 4.91 to 18.26 indicating moderate to high adsorption. Among the three test soils, adsorption was the highest in Ultisol (K_d 18.26), followed by Vertisol (K_d 9.87) and Inceptisol (K_d 4.91). K_F value was also highest for Ultisol soil (66.21), followed by Vertisol (40.88) and Inceptisol (8.59). S-type adsorption isotherms were observed in all the three test soils. K_d values in organic carbon-removed soil and clay-removed soil were 3.57 and 2.83 respectively, indicating lower adsorption than normal Inceptisol. Desorption studies were carried out at initial concentrations of 0.5, 1 and 1.5 μg mL^?1. Desorption was the greatest in Inceptisol, followed by Vertisol and Ultisol. Amounts of pyraclostrobin desorbed in three desorption cycles for different concentrations were 23.1–25.3%, 9.4–20.7% and 8.1–13.6% in Inceptisol, Vertisol and Ultisol respectively. Desorption was higher in clay fraction-removed and organic carbonremoved soils than normal Inceptisol. Desorption was slower than adsorption in all the test soils, indicating hysteresis effect (with hysteresis coefficient values varying from 0.05 to 0.20). Low values of hysteresis coefficient suggest high hysteresis effect indicating easy and strong adsorption, and slow desorption, of pyraclostrobin in soils. Higher hysteresis coefficient values in organic carbon removed soil (0.25–0.30) and clay fraction removed soil (0.28–0.36) as compared to normal Inceptisol soil suggest relatively weak adsorption and easy desorption of pyraclostrobin. Results of regression analysis suggest that the organic matter and pH of the soil play a major role in adsorption of pyraclostrobin. Leaching studies were carried out in intact soil columns in Inceptisol. The columns were leached with different amounts of water simulating different amounts of rainfall. The results suggest that most of the pyraclostrobin residues will remain present in the top soil layers even under high rainfall conditions and chances of pyraclostrobin moving to lower soil depth are almost negligible.     

Tylosin sorption to silty clay loam soils, swine manure, and sand

The objectives of this study were to assess sorption and desorption of tylosin, a macrolide antimicrobial chemical used in swine, cattle, and poultry production, in three silty clay loam soils of South Dakota and compare soil sorption to sand and manure sorption. The silty clay loam soils, from a toposequence in eastern South Dakota, standardized sand samples, and swine manure were used in 24-h batch sorption studies with tylosin concentrations ranging from 25 to 232 micro mole/L. Desorption from soil was conducted over a four-day period. Partition coefficients, based on the Freundlich isotherm (K(f)) or K(d) values, were calculated. K(f) values for the silty clay loams were similar, not influenced by landscape position, and averaged 1,350 with isotherm slopes ranging from 0.85 to 0.93. K(f) values for sand were dependent on solution/sand ratios and pH, ranging from 1.4 to 25.1. K(d) values of manure were dependent on the solution type and ranged from 840 L/kg with urine to about 175 L/kg when sorbed from water. Desorption of tylosin from each soil over the four-day period was < 0.2% of the amount added. The soils' high K(f) values and low desorption amounts suggest that once tylosin is in these soils, leaching to lower depths may not occur. However, this does not preclude runoff with soil eroded particles. If tylosin reaches a sand aquifer, through bypass flow or other mechanism(s), movement in the aquifer most likely would occur.     

毒死蜱在不同土壤腐殖酸上的吸附/解吸特征

通过平衡振荡法研究毒死蜱在不同来源土壤腐殖酸(Has)上的吸附/解吸行为.结果表明,毒死蜱在Has上的等温吸附行为用Freundlich模型描述相对更合理;它们的吸附等温线在实验范围内基本呈直线,且吸附能力很强,顺序为:紫色潮土Has＞黄壤Has＞中性紫色土Has＞酸性紫色土Has＞腐殖土Has;但毒死蜱的解吸率较小,其值均小于26.70%,有明显的滞后现象,尤其是腐殖土Has和紫色潮土Has,固定能力顺序为:紫色潮土Has＞腐殖土Has＞中性紫色土Has＞酸性紫色土Has＞黄壤Has.由于不同来源土壤中Has的组成结构差异明显,它们对毒死蜱的吸附/解吸规律表现出不同的特征.土壤Has对毒死蜱的吸附/解吸行为的影响是多种因素综合作用的结果,具体作用机理尚待进一步研究.     

Geochemical fractions of copper in soil chronosequences of selected European floodplains

The influence of soil formation on copper sorption is documented based on chronosequences of soils from three river floodplains in Europe (Danube, Ebro and Elbe). Sequential extraction was used to fractionate copper in original and spiked soils in order to study the long-term and short-term behaviour of copper retention. Copper partitioning among defined geochemical fractions was mainly determined by soil pH and the contents of carbonates, organic matter and Fe-/Mn-oxides and hydroxides. Copper extracted with NH(2)OH.HCl correlated well with the contents of crystalline Fe-oxides and hydroxides, demonstrating increasing retention capacity with progressing soil development. Copper retained in original soils was found in more strongly bound fractions, whereas sorption of freshly added copper was primarily influenced by the presence of carbonates. Beyond the effect of progressing soil formation, variations in organic carbon contents due to different land use history affected the copper retention capacity of the investigated soils.     

Fate and mobility of pharmaceuticals in solid matrices

The sorption and mobility of six pharmaceuticals were investigated in two soil types with different organic carbon and clay content, and in bacterial biomass (aerobic and anaerobic). The pharmaceuticals examined were carbamazepine, propranolol, diclofenac sodium, clofibric acid, sulfamethoxazole and ofloxacin. The sorption experiments were performed according to the OECD test Guideline 106. The distribution coefficients determined by this batch equilibrium method varied with the pharmaceutical tested and the solid matrix type. Ofloxacin was particularly strongly adsorbed (except of the case of using anaerobic biomass for the solid matrix) while clofibric acid was found to be weakly adsorbed. The fate of pharmaceuticals in soil was also assessed using lysimeters. Important parameters that were studied were: the pharmaceutical loading rate and the hydraulic loading rate for adsorption and the rate and duration of a "rain" event for desorption. Major differences in the mobility of the six pharmaceuticals were observed and correlated with the adsorption/desorption properties of the compounds.     

Sorption, desorption and mineralisation of the herbicides glyphosate and MCPA in samples from two Danish soil and subsurface profiles

The vertical distribution of the sorption, desorption and mineralisation of glyphosate and MCPA was examined in samples from two contrasting soil and subsurface profiles, obtained from a sandy agricultural site and a non-agricultural clay rich site. The highest mineralisation of [14C-methylen]glyphosate, with 9.3-14.7% degraded to 14CO2 within 3 months was found in the deepest sample from the clay site. In the deeper parts of the sandy profile high sorption and low desorption of glyphosate coincided with no or minor mineralisation indicating a limited glyphosate bioavailability. MCPA was readily mineralised except in the deepest samples from both sites. The highest MCPA mineralisation was detected just below the surface layers with 72% or 44% degraded to 14CO2 at the sandy or the clay sites, respectively. MCPA sorped to a minor extent in all samples and no indications of sorption-controlled mineralisation was revealed. None of the herbicides were mineralised under anoxic conditions.