Structural and sorption characteristics of adsorbed humic acid on clay minerals

Clay-humic complexes are commonly distributed in natural environments. They play very important roles in regulating the transport and retention of hydrophobic organic contaminants in soils and sediments. This study examined the structural changes of humic acid (HA) after adsorption by clay minerals and determined phenanthrene sorption by clay-humic complexes. Solid- and liquid-state 13C nuclear magnetic resonance (NMR), for the first time, provided direct evidence for HA fractionation during adsorption on mineral surfaces, that is, aliphatic fractions were preferentially adsorbed by clay minerals while aromatic fractions were left in the solution. The ratio of UV absorbance of HA at 465 and 665 nm (E4 to E6 ratio), which is related to aromaticity, corroborated with the NMR results. For both montmorillonite and kaolinite, adsorbed HA fractions had higher sorption linearity (N) and affinity (K(oc)) than the source HA. The K(oc) of adsorbed HA for the clay-humic complexes could be up to several times higher than that of the source HA. This large increase may be contributed by the low polarity of the bound HA. Moreover, for each mineral, the N values of adsorbed HA increased with increasing HA loading. It is believed that HA may develop a more condensed structure on mineral surface at lower HA loading level due to the stronger interactions between HA and mineral surface as a result of close contacts.     

Chemistry of inorganic arsenic in soils: II. Effect of phosphorus, sodium, and calcium on arsenic sorption

There are more than 10000 arsenic (As) contaminated sites in Australia. The ability of soils at these contaminated sites to sorb As is highly variable and appreciable amounts of As have been recorded in the subsurface soils. The potential risk of surface and ground water contamination by As at these sites is a major environmental concern. Factors that influence adsorption capacity of soils influence the bioavailability and subsequent mobility of As in soils. In the present study we investigated the effect of PO4(3-) and Na+ and Ca2+ on the sorption of AsV and AsIII by an Oxisol, a Vertisol, and two Alfisols. The presence of P (0.16 mmol L(-1)) greatly decreased AsV sorption by soils containing low amounts of Fe oxides (<100 mmol kg(-1)), indicating competitive adsorption between P and AsV for sorption sites. In contrast, the presence of a similar amount of P had little effect on the amount of AsV adsorbed by soils with high Fe content (>800 mmol kg(-1)). However, AsV sorption substantially decreased from 0.63 to 0.37 mmol kg(-1) as P concentration was increased from 0.16 to 3.2 mmol L(-1) in selected soils. This suggests increased competition between P and AsV for soil sorption sites, through either the higher affinity or the effect of mass action of the increasing concentration of P in solution. A similar effect of P on AsIII sorption was observed in the low sorbing Alfisol and high affinity Oxisol. However, the amount of AsIII sorbed by the Oxisol was much greater than the Alfisol for all treatments. The presence of Ca2+ increased the amount of AsV sorbed compared with that of Na+ and was manifested through changes in the surface charge characteristics of the soils. A similar trend in AsIII sorption was recorded with changes in index cation, although the effect was not as marked as recorded for AsV.     

Effects of dissolved organic carbon on sorption and mobility of imidacloprid in soil

To evaluate the effects of dissolved organic carbon on sorption and mobility of the insecticide imidacloprid [1-(6-chloro-3-pyridinyl) methyl-N-nitro-2-imidazolidinimine] in soils, adsorption and column experiments were performed by using a typical calcareous soil from southeastern Spain and two different types of dissolved organic carbon, that is, dissolved organic carbon extracts from a commercial peat (DOC-PE) and high-purity tannic acid (DOC-TA). The experiments were carried out from a 0.01 M CaCl2 aqueous medium at 25 degrees C. The results obtained from the sorption experiments show that the presence of both DOC-PE and DOC-TA, over a concentration range of 15 to 100 mg L(-1), produces in all cases a decreasing amount of imidacloprid adsorbed in the soil studied. From the column experiments the retardation coefficients (RC) were calculated for imidacloprid by using either 0.01 M CaCl2 aqueous solution (RC = 2.10), 0.01 M CaCl2 DOC-PE solution (RC = 1.65), or 0.01 M CaCl2 DOC-TA solution (RC = 1.87). The results indicate that mobility of imidacloprid is increased 21.4 and 11.0% in the presence of DOC-PE and DOC-TA solutions, respectively. Dissolved organic carbon reduces imidacloprid sorption by competing with the pesticide molecules for sorption sites on the soil surface, allowing enhanced leaching of imidacloprid and potentially increasing ground water contamination.     

Sorption of 17β-estradiol to pig slurry separates and soil in the soil-slurry environment

Contamination of freshwater by estrogens from manure applied to agricultural land is of grave concern because of the potentially harmful effects on aquatic life and human health. Recent developments in liquid manure (slurry) management include partial removal of particulate slurry dry matter (PSDM) by separation technologies, which may also remove parts of the estrogens and enhance infiltration of the slurry on field application and hence the interaction between estrogens and the soil matrix. This study investigated how 17β-estradiol (E2), a natural estrogen commonly found in pig manure, sorbs to agricultural soils, to different size fractions of pig slurry separates, and to soils amended with each size fraction to simulate conditions in the soil-slurry environment. A crude fiber fraction (SS1) was prepared by sieving (<500 μm) the solids removed by an on-farm separation process. Three other size fractions (SS2 > SS3 > SS4) were prepared from the liquid fraction of the separated slurry by sedimentation and centrifugation. Sorption experiments were conducted in 0.01 mol L(-1) CaCl(2) and in natural pig urine matrix. Sorption in 0.01 mol L(-1) CaCl(2) was higher than that in pig urine for all solids used. Sorption of E2 to soil increased with its organic carbon content for both liquid phases. The solid-liquid partition coefficients of slurry separates were 10 to 30 times higher than those of soils, but the organoic carbon normalized partition coefficient values, reflecting sorption per unit organic carbon, were lower for slurry separates. Mixing slurry separates with soil increased the sorption of E2 to the solid phase significantly in the order: SS1 < SS3 < SS2 for both liquid phases. In contrast, SS4 reduced the sorption of E2 to the solid phase by increasing the sorption to suspended or dissolved organic matter. The study suggested that potentially 50 to 75% of E2 in slurry can be removed from the liquid fraction of slurry by physical separation.     

Phosphorus sorption and availability in soils amended with animal manures and sewage sludge

Soils that receive large applications of animal wastes and sewage sludge are vulnerable to releasing environmentally significant concentrations of dissolved P available to subsurface flow owing to the gradual saturation of the soil's P sorption capacity. This study evaluated P sorption (calculated from Langmuir isotherms) and availability of P (as CaCl2-P and resin P) in soils incubated for 20 d with poultry litter, poultry manure, cattle slurry, municipal sewage sludge, or KH2PO4, added on a P-equivalent basis (100 mg P kg(-1)). All the P sources had a marked negative effect on P sorption and a positive effect on P availability in all soils. In the cattle slurry- and KH2PO4-treated soils, the decreases in P sorption maximum (19-66%) and binding energy (25-89%) were consistently larger than the corresponding decreases (7-41% and 11-30%) in poultry litter-, poultry manure-, and sewage sludge-treated soils. The effects of cattle slurry and KH2PO4 on P availability were, in most cases, larger than those of the other P sources. In the poultry litter, poultry manure, and sewage sludge treatments, the increase in soil solution P was inversely related (R2 = 0.75) to the input of Ca from these relatively high Ca (13.5-42 g kg(-1)) sources. Correlation analyses implied that the magnitude of the changes in P sorption and availability was not related to the water-extractable P content of the P sources. Future research on the sustainable application of organic wastes to agricultural soils needs to consider the non-P- as well as P-containing components of the waste.     

Herbicide sorption coefficients in relation to soil properties and terrain attributes on a cultivated prairie

The sorption of 2,4-D and glyphosate herbicides in soil was quantified for 287 surface soils (0-15 cm) collected in a 10 x 10 m grid across a heavily eroded, undulating, calcareous prairie landscape. Other variables that were determined included soil carbonate content, soil pH, soil organic carbon content (SOC), soil texture, soil loss or gain by tillage and water erosion, and selected terrain attributes and landform segments. The 2,4-D sorption coefficient (Kd) was significantly associated with soil carbonate content (-0.66; P < 0.001), soil pH (-0.63; P < 0.001), and SOC (0.47; P < 0.001). Upper slopes were strongly eroded and thus had a significantly greater soil carbonate content and less SOC compared with lower slopes that were in soil accumulation zones. The 2,4-D Kd was almost twice as small in upper slopes than in lower slopes. The 2,4-D Kd was also significantly associated with nine terrain attributes, particularly with compounded topographic index (0.59; P < 0.001), gradient (-0.48; P < 0.001), mean curvature (-0.43; P < 0.001), and plan curvature (-0.42 P < 0.001). Regression equations were generated to estimate herbicide sorption in soils. The predicted power of these equations increased for 2,4-D when selected terrain attributes were combined with soil properties. In contrast, the variation of glyphosate sorption across the field was much less dependent on our measured soil properties and calculated terrain attributes. We conclude that the integration of terrain attributes or landform segments in pesticide fate modeling is more advantageous for herbicides such as 2,4-D, whose sorption to soil is weak and influenced by subtle changes in soil properties, than for herbicides such as glyphosate that are strongly bound to soil regardless of soil properties.     

Interactions of organic compounds with wastewater dissolved organic matter: role of hydrophobic fractions

The role of structural fractions of dissolved organic matter (DOM) from wastewater in the sorption process of hydrophobic organic compounds is still not clear. In this study, DOM from two wastewater treatment plants (Lachish and Netanya, Israel) was fractionated to hydrophobic acid (HoA) and hydrophobic neutral (HoN) fractions. The fractions were characterized and their sorptive capabilities for s-triazine herbicides and polycyclic aromatic hydrocarbons (PAHs) were studied. For all sorbates, the binding to the HoN fractions was much higher than to HoA fractions. The HoA fractions were more polar than the HoN fractions, containing a higher level of carboxylic functionalities. However the higher binding coefficients of atrazine (2-chloro-4-ethylamine-6-isopropylamino-s-triazine) and ametryn [2-(ethylamino)-4-isopropylamino-6-methyl-thio-s-triazine] obtained for the HoN fractions suggest that their sorption is governed by hydrophobic-like interactions rather than H bonding. The values of binding coefficients of PAHs measured for the HoN fractions were within the range reported for humic acids and much higher than other fractions, suggesting that this fraction plays an important role in the overall sorption of these compounds by DOM. Higher sorption coefficients were measured for the Netanya DOM sample containing higher level of hydrophobic fractions (HoA + HoN) than the Lachish DOM, suggesting that the sorption of hydrophobic organic compounds by DOM is governed by the level of these structural substances. The evaluation of mobility of organic pollutants by wastewater irrigation requires not only assessment of the total carbon concentration but also, more importantly, the content of the hydrophobic fractions.     

The role of lipids on sorption characteristics of freshwater- and wastewater-irrigated soils

The soil lipid fraction can play an important role in the sorption of organic compounds. In this study, the impact of the lipid fraction of freshwater- and wastewater-irrigated soils on the sorption of non- and relatively polar compounds was assessed. Lipid analyses revealed a clear difference between the two lipid fractions. The lipid extract from the wastewater-irrigated soil was consistent with mainly straight paraffinic chain materials; the lipid extract from freshwater-irrigated soil, on the other hand, exhibited stronger signals of aromatics, double bonds, ester, ether, and methyl, in addition to a smaller contribution from methylene protons. Our data suggest that lipid removal induced a stronger increase in the soil's sorption affinity for solutes capable of polar interactions such as atrazine (2-chloro-4-ethylamino-6-isopropylamino-1,3,5-triazine) and chlorotoluron (N'-(3-chloro-4-methylphenyl)-N,N-dimethylurea) as compared to phenanthrene. Moreover, the level of increase in sorption affinities due to lipid removal was much higher for the freshwater-irrigated soil than for its wastewater-irrigated counterpart, even though the level of lipids in the freshwater-irrigated soil was half that in the wastewater-irrigated one (6 vs. 11% of the total organic C). The higher level of polar functionalities, such as ether and ester moieties, in the lipid fraction from the freshwater-irrigated soil suggests that these extractable compounds compete successfully with the polar solutes (atrazine and chlorotoluron) for specific binding sites in the soil organic matter (SOM). It appears that the composition of the lipid fraction may be a key consideration in unraveling the sorption of organic molecules in soils.     

Interactions of carbamazepine in soil: effects of dissolved organic matter

Pharmaceutical compounds (PCs) and dissolved organic matter (DOM) are co-introduced into soils by irrigation with reclaimed wastewater. We targeted carbamazepine (CBZ) as a model compound to study the tertiary interactions between relatively polar PCs, DOM, and soil. Sorption-desorption behavior of CBZ was studied with bulk clay soil and the corresponding clay size fraction in the following systems: (i) without DOM, (ii) co-introduced with DOM, and (iii) pre-adsorption of DOM before CBZ introduction. Sorption of the DOM to both sorbents was irreversible and exhibited pronounced sorption-desorption hysteresis. Carbamazepine exhibited higher sorption affinity and nonlinearity, and a higher degree of desorption hysteresis with the bulk soil than the corresponding clay size fraction. This was probably due to specific interactions with polar soil organic matter fractions that are more common in the bulk soil. Co-introduction of CBZ and DOM to the soil did not significantly affect the sorption behavior of CBZ; however, following pre-adsorption of DOM by the bulk soil, an increase in sorption affinity and decrease in sorption linearity were observed. In this latter treatment, desorption hysteresis of CBZ was significantly increased for both sorbents. We hypothesize that this was due to either strong chemical interactions of CBZ with the adsorbed DOM or physical encapsulation of CBZ in DOM-clay complexes. Based on this study, we suggest that DOM facilitates stronger interactions of polar PCs with the solid surface. This mechanism can reduce PC desorption ability in soils.     

Concentration, pH, and surface charge effects on cadmium and lead sorption in three tropical soils

Reactions of heavy metals with soil are important in determining metal fates in the environment. Sorption characteristics of two heavy metals, Cd and Pb, in three tropical soils (Mollisol, Oxisol, and Ultisol) from Puerto Rico were assessed at varying metal concentrations (0 to 1.2 mM) and pH values (approximately 2 to 7). All soils sorbed more Pb than Cd. Sorption maxima were obtained for each metal for the Oxisol and Ultisol soils, but not the Mollisol. Sorption appeared to depend more on soil mineralogy than organic matter content. Sorption isotherms were linear within the sorption envelope with similar slopes for each soil-metal curve, when plotting metal sorption as a function of pH. Cadmium and Pb isotherms yielded average slopes of approximately 36+/-1 and 28+/-1 units (percent increase in metal sorption per 1-unit increase in pH), respectively. Metal sorption depended more on metal type than soil composition. Cadmium sorption displayed a greater pH dependence than Pb. Cadmium sorption was less than or equal to the amount of negative surface charge except at pH values greater than the point of zero net charge (PZNC). This suggests that Cd was probably sorbed via electrostatic surface reactions and/or possible inner-sphere complexation at pH > 3.7. However, the amount of Pb sorbed by the Oxisol was greater than the amount of negative surface charge, suggesting that Pb participates in inner-sphere surface reactions. Lead was sorbed more strongly than Cd in our soils and poses less of a threat to underlying ground water systems due to its lower mobility and availability.     

Effect of cobalt sorption on metal fractionation in anaerobic granular sludge

A sequential extraction procedure was applied to two anaerobic methanogenic sludges (Eerbeek and Nedalco) to examine the speciation of micro- and macronutrients in the sludges after cobalt sorption by exposing the sludge to a 1 mM Co solution for 4 d at pH 7 and 30 degrees C. The effect of different physicochemical conditions on cobalt sorption was studied as well: effect of pH (6-8), effect of competition by a second trace element (Ni or Fe), modification of the granular matrix by glutaraldehyde or heat treatment, and EDTA (ethylenediaminetetraacetic acid) addition. Sorbed Co was found to distribute between the carbonates, organic matter + sulfides, and residual fractions. Cobalt adsorption resulted in an antagonistic interaction with other metals present in the granular matrix, evidenced by the solubilization of other trace elements (e.g., Ni, Cu, and Zn) as well as macronutrients (especially Ca and Fe). Modification of the sludge matrix by glutaraldehyde or heat treatment, or exposure to EDTA, led to serious modifications of the Co sorption capacity and strong interactions with multivalent cations (i.e., Ca(2+) and Fe(2+)).     

Influence of decomposition on chemical properties of plant- and manure-derived dissolved organic matter and sorption to goethite

Sorption of dissolved organic matter (DOM) plays an important role in maintaining the fertility and quality of soils in agricultural ecosystems. Few studies have examined the effects of decomposition on DOM sorption and chemical characteristics. This study investigated the sorption to goethite (alpha-FeOOH) of fresh and decomposed hydrophilic (HPL) and hydrophobic (HPB) DOM fractions extracted from the shoots and roots of crimson clover (Trifolium incarnatum L.), corn (Zea mays L.), soybean [Glycine max (L.) Merr.], hairy vetch (Vicia villosa L.), and dairy and poultry manures. Sorption was positively related to apparent molecular weight (MWAP), aromaticity as measured by absorptivity at 280 nm, and phenolic acid content. A 10-d laboratory microbial decomposition of the source organic matter generally increased the sorption of the extracted DOM onto goethite. The decomposition effect on sorption was greater for the HPL fractions than for the HPB fractions. There was a decrease in the MWAP values of the DOM samples following sorption to goethite. In many cases the reduction in MWAP was large, indicating a strong preference by goethite for the higher MWAP DOM fractions. The results of this laboratory-based research demonstrate that microbial processes affect the chemical characteristics of DOM which may affect the distribution of soil organic C pools.     

Nonlinear and competitive sorption of apolar compounds in black carbon-free natural organic materials

Numerous studies have reported a spectrum of sorption phenomena in soils, sediments, and organic matter isolates of those materials that are inconsistent with a partition model proposed in the late 1970s and early 1980s, a model predicated on a hypothesis that sorption is linear and noncompetitive. To explain these nonideal phenomena, prior studies have proposed a hard-soft (glassy-rubbery) model for SOM (soil and sediment organic matter), while others have attributed them singularly to BC (black carbon: soot and charcoal) particles present in topsoils and sediments. In this study, we demonstrated nonideal sorption behavior (isotherm nonlinearity, competitive effects) for a group of apolar compounds in a large set of natural and model organic materials, including a commercial lignin and humic acids from different sources. Complete oxidation of samples by an acidic dichromate method was taken to signify the absence of BC. (However, polymethylene units are stable even if functionalized on both ends, making the technique unreliable for quantifying BC.) Other samples were inferred free of BC by their source and method of preparation. Characterization by thermalanalytical methods indicated the glassy character of the organic materials. The origin of the nonideal behaviors appears to be the glassy character of these materials. Sorption nonlinearity increased or decreased by changing temperature, cosolvent content, or degree of cross-linking by metal ions as predicted for organic solids in a glassy state. We conclude that macromolecular humic substances in the environment may exhibit nonideal sorption behavior in soils and sediments, quite apart from any such behaviors attributable to BC.     

Sorption of sulfonamide pharmaceutical antibiotics on whole soils and particle-size fractions

Residues of pharmaceutical antibiotics are found in the environment, whose fate and effects are governed by sorption. Thus, the extent and mechanisms of the soil sorption of p-aminobenzoic acid and five sulfonamide antibiotics (sulfanilamide, sulfadimidine, sulfadiazine, sulfadimethoxine, and sulfapyridine) were investigated using topsoils of fertilized and unfertilized Chernozem and their organic-mineral particle-size fractions. Freundlich adsorption coefficients (K(f)) ranged from 0.5 to 6.5. Adsorption increased with aromaticity and electronegativity of functional groups attached to the sulfonyl-phenylamine core. Adsorption to soil and particle-size fractions increased in the sequence: coarse silt < whole soil < medium silt < sand < clay < fine silt and was influenced by pH. Sorption nonlinearity (1/n 相似文献   

Regional assessment of herbicide sorption and degradation in two sampling years

Sorption and degradation of the herbicide 2,4-D [2,4-dichlorophenoxyacetic acid] were determined for 123 surface soils (0 to 15 cm) collected in 2002 and in 2004 between 49 degrees to 60 degrees north longitude and 110 degrees to 120 degrees west latitude in Alberta, Canada. The soils were characterized by soil organic carbon content (SOC), pH, electrical conductivity, soil texture, cation exchange capacity, carbonate content, and total soil microbial activity. The 2,4-D sorption coefficients, Kd and Koc, were highly variable with coefficients of variation of 89 and 59%, respectively, at the provincial scale. Both Kd and Koc were well described by regression models with SOC and soil pH as variables, regardless of scale. Surprisingly, variations in 2,4-D mineralization were much smaller than variations in sorption. Variability in total 2,4-D mineralization was particularly low, with a coefficient of variation of only 7% at the provincial scale. Average 2,4-D half-lives in ecoregions ranged from 1.7 to 3.5 d, much lower than the field dissipation half-life of 10 d reported for 2,4-D in general pesticide property databases. Regression models describing degradation parameters were generally poor or not significant because 2,4-D mineralization was only weakly associated with measured 2,4-D sorption parameters and soil properties. As such, regional variations in herbicide sorption coefficients should be measured or calculated based on soil properties, to assign distinct pesticide fate model input parameters when estimating 2,4-D off-site transport at the provincial scale. Spatial variations in herbicide degradation appear less important for Alberta as 2,4-D half-lives were similar in soils across the province. The rapid mineralization of 2,4-D is noteworthy because 2,4-D is widely used in Alberta and perhaps adaptation of soil microbial communities allowed for accelerated degradation regardless of soil properties or the extent of 2,4-D sorption by soil.     

Effect of heat treatment on sorption of polar and nonpolar compounds to montmorillonites and soils

Batch sorption isotherms of 1,3,5-trichlorobenzene, 1,3,5-trinitrobenzene, and tetracycline to organic-free montmorillonites and soils receiving heat treatment (375°C for 24 h) were compared with those to unheated sorbents. Sorption of the nonpolar 1,3,5-trichlorobenzene to soil was lowered after the removal of humus by heating, consistent with the mechanism of hydrophobic partition into organic matter. For 1,3,5-trinitrobenzene, the enhanced sorption to heated soils was attributed to specific interactions with exchangeable cations facilitated by heating-induced irreversible partial dehydration of the clay interlayer. For tetracycline, an additional mechanism for sorption enhancement could be due to increased exposure of strong complexation sites on clay minerals after removal of the humic coating. These hypotheses were supported by the sorption data to heated and unheated Na-, K-, and Cs-saturated montmorillonites. The combustion method is commonly adopted to measure the content of black carbon in soils and sediments. However, findings from the present study indicate that combustion may greatly modify the structural properties of clay minerals, leading to misinterpreted sorption contributions of different soil components to sorption of polar or ionic compounds.     

Significance of anion exchange in pentachlorophenol sorption by variable-charge soils

Sorption data and subsequent predictive models for evaluating acidic pesticide behavior on variable-charge soils are needed to improve pesticide management and environmental stewardship. Previous work demonstrated that sorption of pentachlorophenol (PCP), a model organic acid, was adequately modeled by accounting for pH-and pKa-dependent chemical speciation and using two organic carbon-normalized sorption coefficients; one each for the neutral and anionic species. Such models do not account for organic anion interaction to positively charged surface sites, which can be significant for variable-charge minerals present in weathered soils typical of tropical and subtropical regions. The role of anion exchange in sorption of ionizable chemicals by variable-charge soils was assessed by measuring sorption of PCP by several variable-charge soils from aqueous solutions of CaCl2, CaSO4, Ca(H2PO4)2 as a function of pH. Differences in sorption from phosphate and chloride electrolyte solutions were attributed to pentachlorophenolate interactions with anion exchange sites. Suppression of PCP sorption by phosphate ranged from negligible in a soil with essentially no positively charge sites, as measured by negligible anion exchange capacity, to as much as 69% for variable-charge soils. Pentachlorophenolate exchange correlated well with the ratio of pH-dependent anion exchange capacity to net surface charge. Sorption reversibility of PCP by both CaCl2 and Ca(H2PO4)2 solutions was also demonstrated. Results for PCP clearly demonstrate that sorption to anion exchange sites in variable-charge soils should be considered in assessing pesticide mobility and that phosphate fertilizer application may increase the mobility of acidic pesticides.     

Soil carbon storage in silvopastoral systems and a treeless pasture in northwestern Spain

Soil particle size and land management practices are known to have considerable influence on carbon (C) storage in soils, but such information is lacking for silvopastoral systems in Spain. This study quantified the amounts of soil C stored at various depths to 100 cm under silvopastoral plots of radiata pine ( D. Don) and birch ( Roth) in comparison to treeless pasture in Galicia, Spain. Soils were fractionated into three size classes (<53, 53-250, and 250-2000 μm), and C stored in them and in the whole (nonfractionated) soil was determined. Overall, the C stock to 1 m ranged from 80.9 to 176.9 Mg ha in these soils. Up to 1 m depth, 78.82% of C was found in the 0- to 25-cm soil depth, with 12.9, 4.92, and 3.36% in the 25- to 50-, 50- to 75-, and 75- to 100-cm depths, respectively. Soils under birch at 0 to 25 cm stored more C in the 250- to 2000-μm size class as compared with those under radiata pine; at that depth, pasture had more C than pine silvopasture in the smaller soil fractions (<53 and 53-250 μm). In the 75- to 100-cm depth, there was significantly more storage of C in the 250- to 2000-μm fraction in both silvopastures as compared with the pasture. The higher storage of soil C in larger fraction size in lower soil depths of silvopasture suggests that planting of trees into traditional agricultural landscapes will promote longer-term storage of C in the soil.     

Batch sorption dynamics and equilibrium for the removal of lead ions from aqueous phase using activated carbon developed from coffee residue activated with zinc chloride

Lignocellulosic materials are good precursors for the production of activated carbon. In this work, coffee residue has been used as raw material in the preparation of powder activated carbon by the method of chemical activation with zinc chloride for the sorption of Pb(II) from dilute aqueous solutions.The influence of impregnation ratio (ZnCl₂/coffee residue) on the physical and chemical properties of the prepared carbons was studied in order to optimize this parameter. The optimum experimental condition for preparing predominantly microporous activated carbons with high pore surface area (890 m²/g) and micropore volume (0.772 cm³/g) is an impregnation ratio of 100%. The developed activated carbon shows substantial capability to sorb lead(II) ions from aqueous solutions and for relative impregnation ratios of 75 and 100%, the maximum uptake is practically the same. Thus, 75% represents the optimal impregnation ratio.Batch experiments were conducted to study the effects of the main parameters such as contact time, initial concentration of Pb(II), solution pH, ionic strength and temperature. The maximum uptake of lead(II) at 25 °C was about 63 mg/g of adsorbent at pH 5.8, initial Pb(II) concentration of 10 mg/L, agitation speed of 200 rpm and ionic strength of 0.005 M. The kinetic data were fitted to the models of pseudo-first order and pseudo-second order, and follow closely the pseudo-second order model. Equilibrium sorption isotherms of Pb(II) were analyzed by the Langmuir, Freundlich and Temkin isotherm models. The Freundlich model gives a better fit than the others.Results from this study suggest that activated carbon produced from coffee residue is an effective adsorbent for the removal of lead from aqueous solutions and that ZnCl₂ is a suitable activating agent for the preparation of high-porosity carbons.     

Phosphorus sorption characteristics of estuarine sediments under different redox conditions

Phosphorus (P) plays a major role in eutrophication of aquatic systems. Estuarine sediments could function as sources or sinks for P to the overlying water column depending upon their physico-chemical characteristics. Understanding of P sorption phenomena in estuarine sediments is important in regulating the P availability in estuaries. Phosphorus sorption characteristics of sediments from the Indian River Lagoon, Florida, USA, were determined to examine the role of selected physico-chemical properties of the sediments on soluble reactive P status in estuary water. Mean equilibrium P concentrations (EPCo) of 0.75 mg L(-1) and mean P sorption maxima (Smax) of 32.2 mg kg(-1) were obtained under anaerobic conditions, compared with EPCo of 0.05 mg L(-1) and Smax of 132.7 mg kg(-1) under aerobic conditions. The higher EPCo values under anaerobic conditions and the greater Smax values under aerobic conditions were associated with amorphous and poorly crystalline iron. These results suggest that sediments enriched with amorphous and poorly crystalline forms of iron act as an excellent reservoir for P by adsorbing excessive P in aerobic sediment zones and releasing it upon burial under anaerobic conditions. This study also indicates that P compounds in sediments independently maintain equilibrium with P in solutions. Thus, heterogeneous systems like soil and sediment simply behave as a mixture of homogeneous surfaces as far as their P sorption characteristics are concerned, and hence can be successfully described by the Langmuir and Freundlich models.