Chlorophenol binding to dissolved and particulate soil organic matter determined in controlled equilibrium systems

We determined the sorption of 2,4‐dichlorophenol (DCP), 2,4,5‐trichlorophenol (TCP) and pentachlorophenol (PCP) to dissolved (DOM) and particulate soil organic matter (POM) from the same soil in controlled equilibrium systems, using ¹⁴C‐labelled chlorophenols in combination with reversed‐phase high‐performance liquid chromatography (RP‐HPLC) and liquid scintillation. Associations of DCP, TCP and PCP to DOM and POM were satisfactorily described by linear adsorption isotherms. Together with the absence of substantial competition between DCP and TCP for binding sites, this indicates a hydrophobic partitioning mechanism. The organic carbon normalized partitioning coefficient (K_OC) for the binding of DCP was similar in magnitude for POM (K_POC) and for DOM (K_DOC), whereas K_POC for the more hydrophobic compounds TCP and PCP were approximately one order of magnitude greater than K_DOC. On the basis of the relationships between log K_OC and the organic carbon normalized partitioning coefficient (log K_OW), the extent of association to POM increases more with the hydrophobicity of the chlorophenol than the extent of association to DOM. This holds for our data obtained for DOM and POM of similar origin, as well as for various sources of POM and DOM reported in the literature. Differences in the magnitude of K_POC and K_DOC in our study could not be accounted for by differences in gross carbon chemistry of POM and DOM, as determined by nuclear magnetic resonance (¹³C‐NMR) and X‐ray photoelectron spectroscopy (XPS). Thus, other factors such as the average size and capacity of hydrophobic moieties could explain differences in chlorophenol association between POM and DOM. We conclude that K_POC and K_DOC need to be determined explicitly, when the transport and retention of chlorophenols is modelled, and not calculated from relationships between log K_OC and log K_OW.     

Effects of tillage practice and repeated urban compost application on bromide and isoproturon transport in a loamy Albeluvisol

We quantified the effects of tillage practice and repeated compost (municipal solid waste compost, MSW, and co‐compost of sewage sludge and green wastes, SGW, compared with a control plot without compost addition, CONT) application on bromide and isoproturon transport into the tilled horizon of a loamy Albeluvisol. To do this we conducted field measurements of near‐saturated hydraulic conductivity (K), bromide and isoproturon leaching in column experiments and batch isoproturon sorption measurements. While the K measurements showed that tillage practice had the major effect compared with the different organic amendments, with greater conductivities measured after ploughing and smaller Kvalues measured after sowing, the column leaching experiments showed no statistically significant effect of either the tillage practice or the compost amendments. The batch sorption coefficient, K_d, of isoproturon increased in the order CONT < MSW < SGW, while the leaching of isoproturon for the MSW and SGW was either equal, retarded or quicker compared with CONT. Rate‐limited sorption of isoproturon in the CONT and SGW treatments columns was found, and the overall dissipation of isoproturon increased in the order CONT < SGW < MSW. It was suggested that irreversible sorption as well as degradation occured during isoproturon leaching.     

BTEX Sorption by Montmorillonite Organo-Clays: TMPA,Adam, HDTMA

Organo-clay can be utilized for the containment of environmentalpollutants originating from waste sites or accidental spills. Abatch study was conducted using organo-clays produced from aWyoming montmorillonite (SWy) and three organic cations(trimethylphenylammonium (TMPA), trimethylammonium adamantane(Adam), and hexadecyltrimethylammonium (HDTMA)) to characterizeBTEX (benzene, toluene, ethylbenzene, o-, m-, p-xylene) sorption. Sorption data were fitted to two models,with Freundlich resulting in greater correlations of the datathan the Langmuir model (R ² at P ≤0.001-0.05). The Freundlich conditional index (n _f),which describes the experimental sorption characteristics,decreased curvilinearly with organic-cation molecular weights,thus suggesting organo-clays with smaller cations had greaterhydrocarbon retention. Sorption of BTEX followed the order ofTMPA > Adam > HDTMA organo-clays. A similar sequence in themagnitudes of log K _d and log K _omsupportedthis finding. Positive log K _om/K _ow valuesfor TMPA and Adam derivatives indicated there was a greaterretention of BTEX by these organo-clays than octanol. The orderof log K _om for SWy-HDTMA, although concentration-dependent, was analogous to the log K _ow order,indicating partitioning was the dominant sorption mechanism forthe HDTMA-clay. Isotherms for SWy-TMPA and SWy-Adam followed aconvex up pattern. In contract, a concave up curvature, notedfor SWy-HDTMA isotherms, was probably caused by a cosorptiveenhancement process resulting from an effective increase in organic matter content of the organo-clay due to furtherhydrocarbon sorption,in concurrence with a decrease inadsorbate activity coefficients. Values of binding affinityconstant, K _f, for SWy-TMPA were consistently higherthan SWy-Adam. The K _f values determined for totalBTEX sorption by TMPA and Adam derivatives were higher thanthose for the individual hydrocarbons. With SWy-HDTMA, the same order was observed for benzene and toluene; however, ethylbenzene and xylenes had greater K _f values thanthat for the BTEX mixture, possibly due to higher partitioningaffinity of the larger alkylbenzenes. With SWy-HDTM, thesequence of K _f values was: ethylbenzene > m-xylene > p-xylene > o-xylene > toluene >benzene. Trends for SWy-TMPA and SWy-Adam were in contrast tothat of the partitioning order, suggesting that adsorption, ratherthan partitioning, was the primary sorption mechanism for thesetwo organo-clays. With respect to the equilibriumconcentrations, the sorbed amounts for total BTEX mixture weregenerally higher than those for the individual compounds. Ascompared to benzene and toluene, the large-size alkylbenzenesshowed greater partitioning affinity due to their high hydrophobicity.     

Impacts of particulate organic carbon and dissolved organic carbon on removal of polycyclic aromatic hydrocarbons, organochlorine pesticides, and nonylphenols in a wetland

Background, aim, and scope  The potential of wetlands for controlling point- and nonpoint-source pollution in surface water has attracted increasing interest. The partitioning process of organic contaminants between water, particulate organic carbon (POC) and dissolved organic carbon (DOC), impacts their behaviors in the aquatic environments. Meantime, the partitioning process of organic contaminants is closely related to their physicochemical properties, such as hydrophobicity (or K _ow), and their fates in wetlands may vary greatly depending on physicochemical properties. The aim of this study was to examine fates and removals of polycyclic aromatic hydrocarbons (PAHs), organochlorine pesticides (OCPs) and nonylphenols (NPs) in a wetland in Beijing, China, and provide useful information for ecological remediation. Materials and methods  Water samples, collected at five sites from inlet to outlet of the wetland once a month in summer 2006, were immediately filtered within 2 days through 0.45-μm glass fiber prefilters and enriched by solid-phase extraction. The filtered particulates were collected as the total suspended particulates (TSPs), freeze-dried, and Soxhlet-extracted. After extraction, samples were purified following a clean-up procedure and analyzed by GC-MS. Results  TSPs could be removed efficiently with a removal rate of 97.4%, and DOC could be moderately removed with a removal rate of 44.7% from inlet to outlet. The total removals of target contaminants varied widely from null to 82.0%. A good correlation between logK _ow and logK _oc (organic-carbon-normalized suspended-particulate partition coefficient) was observed (r ² = 0.84 for PAHs and r ² = 0.86 for OCPs, p < 0.01). Ratios of the POC-bound fraction of target contaminants (or DOC-bound fraction) to the freely dissolved fraction increased with their K _ow values. The removal of the POC fraction contributed more than 50% to the total removal for the contaminants with logK _ow > 5.0. Only a small portion of the removal was attributed to the removal of the freely dissolved fraction. Discussion  Hydrophobic compounds such as PAHs and OCPs with higher K _ow values would show stronger POC or DOC preference. Their removal depended greatly on their K _ow values and the removal of total suspended particulates. On the other hand, concentrations of NPs decreased little in the wetland, probably due to their production through degradation of their precursors and relatively low hydrophobicity. Conclusions  POC and DOC play essential roles on the fates and removals of hydrophobic organic contaminants in the wetland. The removal of target contaminants with a high K _ow should be mainly through association with the suspended particulates which were precipitated and retained in the wetland. The fates of the organic contaminants in the wetland greatly depended on their hydrophobicities. Recommendations and perspectives  Further work should be done to study the influence of hydraulic retention time and some other environmental factors, e.g., temperature, on removals and fates of organic contaminants. Behavior of NPs and their precursors in the wetland should also be investigated more thoroughly.     

Multi-Step Competitive Sorption and Desorption of Chlorophenols in Surfactant Modified Montmorillonite

Single- and bi-solute sorption and desorption of 2,4-dichlorophenol (2,4-DCP) and 2,4,5-trichlorophenol (2,4,5-TCP) in montmorillonite modified with hexadecyltrimethylammonium (HDTMA) were investigated using multi-step sorption and desorption procedure. Effect of pH on the multi-step sorption and desorption was investigated. As expected by the magnitude of octanol-water partition coefficient, K _ow , both sorption and desorption affinity of 2,4,5-TCP was higher than that of 2,4-DCP at pH 4.85 and 9.15. For both chlorophenols, the protonated speciation (at pH 4.85) exhibited a higher affinity in both sorption and desorption than the predominant deprotonated speciation (about 95% and 99% of 2,4-dichlorophenolate and 2,4,5-trichlophenolate anions at pH 9.15, respectively). Desorption of chlorinated phenols was strongly dependent on the current pH regardless of their speciation in the previous sorption stage. Freundlich model was used to analyze the single-solute sorption and desorption data. No appreciable desorption-resistant (or non-desorbing) fraction was observed in organoclays after several multi-step desorptions. This indicates that sorption of phenols in organoclay mainly occurs via partitioning into the core of the pseudo-organic medium, thereby causing desorption nearly reversible. In bisolute competitive systems, sorption (or desorption) affinity of both chlorophenols was reduced compared to that in its single-solute system due to the competition between the solutes. The ideal adsorbed solution theory (IAST) coupled to the single-solute Freundlich model successfully predicted bisolute multi-step competitive sorption and desorption equilibria.     

Partitioning characteristics of PAHs between sediment and water in a shallow lake

Goal, Scope and Background

Distribution of hydrophobic organic contaminants in abiotic compartments is essential for describing their transfer and fate in aquatic ecosystems. Taihu Lake is the third largest freshwater lake in China. Water quality of Taihu Lake has deteriorated greatly during the last decades and has threatened the water supply. The aim of the present study was to investigate the partitioning of polycyclic aromatic hydrocarbons (PAHs) among overlying water, suspended particulate matter (SPM), sediments, and pore water in Meiliang Bay, Taihu Lake and to provide useful information for the ecological engineering in this area.

Materials and Methods

Overlying water and surface sediment were sampled from six sites in Meiliang Bay, Taihu Lake, China. Within 72 h of sampling, sediments were centrifuged to obtain the pore water. Overlying water samples were filtered to separate dissolved and SPM samples. After extraction, samples were purified following a clean-up procedure. PAH fraction was obtained by elution with a mixture of hexane: DCM (7:3, V/V) and analyzed by GC/MS.

Results

PAHs concentrations in overlying water varied from 37.5 ng/L to 183.5 ng/L. Concentrations of PAHs in pore water were higher than those in overlying water. The total concentrations of 16 priority PAHs in sediments ranged from 2091.8 ng/g-dw to 4094.4 ng/g-dw. PAHs concentrations on SPM were decreased with suspended solid concentrations (SSC). Total PAHs concentrations on SPM varied in the range of 3369.6 ng/g-dw to 7531.1 ng/g-dw. The partition coefficients between sediment and overlying water (log K _oc) for PAHs with log K _ow<5 were positively correlated with their octanol-water partition coefficients (log K _ow) (n=39, r=0.79, p<0.0001). Partition coefficients between sediment and pore water (log K _oc′) for all PAHs were also significantly correlated with their log K _ow values (n=48, r=0.82, p<0.0001).

Discussion

In general, PAHs derived from combustion sources tend to bind strongly to soot particles in natural sediment. Consequentially, K _oc values observed in the natural environment could be orders of magnitude higher than those predicted by linear correlation relationships under laboratory conditions. In the present study, the ratio of log K _oc values to log K _ow values falls consistently above 1, indicating that the sediment soot carbon in the bay was more attractive for PAHs than n-octanol. The log K _oc′ was also higher than that predicted under laboratory conditions, suggesting that the measured pore water PAH concentrations were lower than those predicted. That is to say, not all the sediment PAHs can be available to partition rapidly into sediment pore waters. A variation in soot content is a possible reason. Furthermore, concentrations of PAHs on SPM were higher than those in sediments. The compositions of PAHs on SPM and in sediments were similar, indicating the importance of re-suspension process of sediments in the partitioning process of the shallow lake.

Conclusions

The results indicated the equilibrium partitioning model could be used to predict PAHs distribution in various phases of a shallow lake in the stagnation period, but re-suspension processes should be considered to modify the relationship between log K _ocs and log K _ows.

Recommendations and Perspectives

Concentration, particle size and composition of resuspended particles could affect the relationship between log K _ocs and log K _ows. Further work should be done under field conditions, especially where a steady thermodynamic equilibrium state could be assumed.

     

Biochar Increases Diuron Sorption and Reduces the Potential Contamination of Subsurface Water with Diuron in a Sandy Soil

The herbicide diuron is widely used in agricultural areas in Brazil, whereas it has high potential for subsurface water contamination due to its physicochemical characteristics. Recent studies have demonstrated the potential of biochar as a sorbent and possible pesticide leaching mitigation. The objective of this study was to investigate the long-term effect of biochar application on the kinetics of sorption and desorption of diuron in a Cerrado Haplic Plinthosol. Samples were collected in an experiment conducted in the field in a randomized block design consisting of the combination of two levels of fertilizer application (0 and 300 kg ha^-1 of 5-25-15 formula of NPK fertilizers) and three doses of biochar (0, 16, and 32 Mg ha^-1). The Freundlich isotherm accurately described the sorption of diuron in all treatments. Biochar application increased the sorption and reduced the desorption of diuron. This effect was attributed to the contribution of biochar to total organic carbon (C) and C in the humin fraction and to the increase in the reactivity of the humic acid and humin fractions, which was significantly highly correlated with the sorption coefficient (K_f). A positive correlation between the partition coefficient of organic C and K_f confirmed the importance of the soil organic compartment for the sorption of diuron. The higher diuron sorption and lower diuron desorption capacities of sandy soils after biochar application could reduce the potential risk of diuron leaching and contamination of subsurface water.     

Cadmium sorption behavior of natural and synthetic zeolites

Abstract

The sorptive properties of zeolites (a natural zeolite and 3 synthetic zeolites) for cadmium (Cd) were investigated with the intention of selecting suitable materials, for use as amendments in contaminated soils, to reduce the uptake of Cd by field crops. The Cd sorption data were well described by the Langmuir and the Freundlich equations and the coefficients values indicated significant sorptive capacities for Cd by these minerals. Synthetic zeolites have 100 to 500 times greater sorption capacities than the natural zeolite. In all cases, sorption increased with increasing pH and this relationship was linear over the pH range between 3 and 10 for the natural zeolite whereas for the synthetic zeolites a sharp increase was observed between pH 3 and 6. The critical pH above which maximum Cd sorption occurred on synthetic zeolites coincided with the pH where mineral dissolution ceases. The natural zeolite showed an inverse relationship between particle size (<0.15–2.0 mm) and Cd sorption. In desorption experiments with natural zeolite, 10 sequential extractions with 0.01 MNaC10₄ removed 19% Cd from the lowest sorption treatment and 44% of the metal from the highest level, showing that Cd was bound more strongly with decreasing concentrations. Desorption was greater with 0.01 MKC10₄than 0.01 MNaC10₄ especially in the first 5 extractions.     

Adapted DAX‐8 fractionation method for dissolved organic matter (DOM) from soils: development,calibration with test components and application to contrasting soil solutions

Most methods to fractionate natural dissolved organic matter (DOM) rely on sorption of acidified DOM samples onto XAD‐8 or DAX‐8 resin. Procedural differences among methods are large and their interpretation is limited because there is a lack of calibration with DOM model molecules. An automated column‐based DOM fractionation method was set up for 10‐ml DOM samples, dividing DOM into hydrophilic (HPI), hydrophobic acid (HPOA) and hydrophobic neutral (HPON) fractions. Fifteen DOM model components were tested in isolation and in combination. Three reference DOM samples of the International Humic Substances Society were included to facilitate comparison with other methods. Aliphatic low‐molecular‐weight acids (LMWAs) and carbohydrates were classified as HPI DOM, but some LMWAs showed also a partial HPO character. Aromatic LMWAs and polyphenols partitioned in the HPOA fraction, menadione (quinone) and geraniol (terpenoid) in HPON DOM. Molecules with log K_ow > 0.5 had negligible HPI fractions. The HPO molecules except geraniol had specific UV absorbance (SUVA, measure for aromaticity) >3 litres g⁻¹ cm⁻¹ while HPI molecules had SUVA values <3 litres g⁻¹ cm⁻¹. Distributions of DOM from eight soils ranged from 31 to 72% HPI, 25 to 46% HPOA and 2 to 28% HPON of total dissolved organic carbon. The SUVA of the HPI DOM was consistently smaller compared with the HPOA DOM. The SUVA of the natural DOM samples was not explained statistically by fractionation and the variation coefficient of SUVA among samples was not reduced by fractionation. Hence, fractionation did not reduce the variability in this DOM property, which casts some doubts on the practical role of DOM fractionation in predicting DOM properties.     

Desorption of myo‐inositol hexakisphosphate and phosphate from goethite by different reagents

Inositol phosphates are abundant organic phosphates found widely in the environment. The sorption and desorption of organic phosphate (P_o) are important processes in controlling the mobility, bioavailability and fate of phosphorus (P) in soil and sediment. The desorption characteristics of myo‐inositol hexakisphosphate (IHP) and inorganic phosphate (P_i) from goethite were studied by pre‐sorption of IHP or P_i followed by desorption by KCl, H₂O, and citrate. Batch experiments and in situ attenuated total reflectance Fourier transform infrared (ATR‐FTIR) spectroscopy were used to investigate the desorption of IHP/P_i. The desorption percentage of IHP/P_i by citrate was much higher than that by H₂O/KCl. The desorption of P by citrate was mainly achieved through ligand exchange, and the desorption increased with decreasing pH. Desorption by H₂O was slightly greater than that by 0.02 M KCl because the electrostatic repulsion between the P molecules is larger in H₂O. Due to the higher affinity of IHP for goethite than that of P_i, the maximum desorption of IHP was lower than that of P_i. Desorption curves (desorption concentration in solution vs. sorption density) of IHP or P_i on goethite by KCl or H₂O was well fitted by an exponential equation, while those by citrate were well fitted by a linear equation. The desorption amounts of P in the first cycle account for more than 58% of the total desorption followed by substantial decreases in the second and third cycles. There was a re‐sorption of P_i from solution in the late stage of desorption by KCl and H₂O, resulting in a sharp decrease in desorption. Re‐sorption of IHP did not occur, which is probably due to its poor diffusion into goethite. The initial desorption rate of P_i with KCl and H₂O decreased with increasing pre‐sorption time, whereas that of IHP was opposite. This study indicates that strong sorption on and weak desorption of IHP from iron (hydr)oxides may explain the accumulation of IHP in soils.     

Congener-specific evaluation of biota-sediment accumulation factor model for HCHs and DDTs under small-scale in situ riverine condition

Purpose

The congener-specific biota-sediment accumulation factors (BSAFs) model for hexachlorocyclohexanes (HCHs) and dichlorodiphenyltrichloroethanes (DDTs) was evaluated for four different freshwater fish species (Orienus plagiostomus, Tor putitora, Glyptothorax punjabensis, and Cyprinus carpio) in in situ riverine conditions of Kabul River, Pakistan.

Materials and methods

The congeners of HCH and DDT were quantified using gas chromatograph (GC-ECD). The BSAF for each congener (HCHs and DDTs) was calculated from paired observation of congener’s measured concentrations in fish and sediment taken at the same site. Pearson’s correlation and linear regression analyses were performed to determine the influence of sediment organic carbon fraction (f _soc ) and organism lipid fraction (f _lipid ) on BSAF, and the relationship between BSAFs and logarithm of octanol-water partition coefficients (log K _ows) of HCH and DDT congeners, respectively.

Results and discussion

The BSAFs for total HCH (t-HCH) and total DDT (t-DDT) ranged from 0.6 to 1.5 and from 0.2 to 1.6, respectively. The model was significantly influenced by both fish (p = 0.004) and chemical types (p = 0.002) at 95 % confidence level. The sediment organic carbon fraction (f _soc ) and fish lipid fraction (f _lipid ) had not-too-weak effects on BSAF values for all fish species. The BSAF values were linearly fitted with logarithmic octanol-water partition coefficients (log K _ows) of HCH and DDT congeners, despite the different chemical structures, and different compound class significant negative correlations between log K _ows and BSAF values were found, indicating that hydrophobicity is one of the key factors influencing the bioaccumulation potential of the investigated compounds.

Conclusions

The present study confirmed the applicability of the BSAF model as a screening tool for predicting bioaccumulation of sediment-associated HCH and DDT congeners in investigated fish species under small-scale in situ riverine conditions of Kabul River and suite the model for benthic fish (G. punjabensis) on the basis of the 25th and 75th percentiles of congener-specific BSAF values.

     

Caesium sorption—desorption in clay—humic acid systems

Soaking for 7 d with 0.05 M NaCl resulted in less caesium being sorbed by bentonite and kaolinite, but more by illite, compared to soaking for 2 d prior to addition of Cs. Overall the amount of Cs sorbed by the three clays was in the order bentonite > illite > kaolinite. Addition of humic acid to the clays depressed the sorption of Cs by all three clays, with illite showing the greatest effect. Desorption of added Cs was not totally reversible. The presence of humic acid resulted in an enhanced desorption of Cs from bentonite and to a lesser extent kaolinite. This enhanced desorption in the presence of humic acid was not seen for illite. The order of Cs retention following desorption for both clay and clay/ humic-acid mixtures was illite > bentonite > kaolinite. A single K_d value could not describe the whole isotherm, but individual values were calculated at different Cs concentrations to cover the range of the isotherm. K_d values for desorption were higher than the corresponding K_d for sorption. For both sorption and desorption, the presence of humic acid resulted in lower K_d values than in its absence.     

Soil hydrophobicity: a contribution of diuron sorption experiments

Retention processes play a major role in the fate and impact of organic contaminants in soils. The main goal of this study was to determine the influence of soil hydrophobic properties on the retention of diuron by using plots of a long‐term experiment in Versailles. We selected seven plots with pH 3.4 to 8.2 and low organic content. Sorption isotherms were obtained on soil slurries and kinetic measurements of diuron sorption were performed on undisturbed soil samples. The results showed that the Freundlich coefficient k_f decreased as pH increased and that the K_oc coefficient, k_f/TOC, was linearly related to the contact angle measured on the clay fraction over a wide range of pH. A low initial adsorption rate and low adsorption equilibrium were observed for the plot treated with NaNO₃. In this case, the structure in micro‐aggregates was assumed to limit the accessibility of adsorption sites. The CaCO₃ and CaO treated plots had similar organic matter contents, pHs, CECs and bulk densities, although their < 2 μm:C ratio differed. The higher retention of diuron in the CaCO₃ plot is attributed to the higher hydrophobicity of the < 2 μm fraction, probably masking part of the permanent clay negative charges. Thus, in addition to the different treatments, organic matter composition and distribution should also be included as specific soil properties. We conclude that the sorption properties of pesticides such as diuron can be a good tool to obtain greater understanding of soil properties and the degree of soil hydrophobicity/hydrophilicity in particular.     

土壤对镉的吸附与解吸——Ⅱ.吸附势与解吸势

本文提出了吸附势(logK_a)和解吸势(logK_d或相对解吸势logK_dr)两个有关吸附和解吸的强度概念,并进行了理论推导和实验验证。logK_a和logK_d或logK_dr是影响土壤或胶体吸附和解吸因素的综合反应。实验证实logK_a可用于表征土壤胶体对Cd的相对选择性,并且对胶体吸附Cd有着良好的预测性;logK_dr可用于表征土壤胶体对Cd的相对固定能力,并可用于估测Cd的污染程度。盆栽试验表明,随着土壤胶体logK_a的增加,或logK_dr的降低,稻草或糙米中Cd的含量下降。可以预期,吸附势和解吸势不但在土壤物理化学,土壤环境化学研究中,而且在植物营养化学、水化学、以及界面化学等方面有可能获得实际应用。     

Response of the sorption behavior of Cu,Cd, and Zn to different soil management

This study investigated the effect of different farming practices over long time periods on the sorption‐desorption behavior of Cu, Cd, and Zn in soils. Various amendments in a long‐term field experiment over 44 y altered the chemical and physical properties of the soil. Adsorption isotherms obtained from batch sorption experiments with Cu, Cd, and Zn were well described by Freundlich equations for adsorption and desorption. The data showed that Cu was adsorbed in high amounts, followed by Zn and Cd. In most treatments, Cd ions were more weakly sorbed than Cu or Zn. Generally, adsorption coefficients K_F increased among the investigated farming practices in the following order: sewage sludge ≤ fallow < inorganic fertilizer without N ≈ green manure < peat < Ca(NO₃)₂ < animal manure ≤ grassland/extensive pasture. The impact of different soil management on the sorption properties of agricultural soils for trace metals was quantified. Results demonstrated that the soil pH was the main factor controlling the behavior of heavy metals in soil altered through management. Furthermore, the constants K_F and n of isotherms obtained from the experiments significantly correlated with the amount of solid and water‐soluble organic carbon (WSOC) in the soils. Higher soil pH and higher contents of soil organic carbon led to higher adsorption. Carboxyl and carbonyl groups as well as WSOC significantly influenced the sorption behavior of heavy metals in soils with similar mineral soil constituents.     

Factors controlling the partitioning of pyrene to dissolved organic matter extracted from different soils

The mobility of hydrophobic organic compounds (HOCs) in soils can be influenced by the presence of dissolved organic matter (DOM). While numerous studies have determined interactions of HOCs with humic and fulvic acids, only few data exist on the partitioning of HOCs to natural, non‐fractionated DOM as it occurs in soil solutions. In this study, DOM was extracted from 17 soil samples with a broad range of chemical and physical properties, originating from different land uses. The partition coefficients of pyrene to DOM were determined in all soil extracts and for two commercial humic acids using the fluorescence quenching method. For the soil extracts, log K_DOC values ranged from 3.2 to 4.5 litres kg^?1. For the Aldrich and Fluka humic acids, log K_DOC was 4.98 and 4.96 litres kg^?1, respectively, thus indicating that they are not representative for soil DOM. After excluding these two values, the statistical analysis of the data showed a significant negative correlation between log K_DOC and pH. This was also shown for one sample where the pH was adjusted to values ranging from 3 to 9. A multiple regression analysis suggested that ultraviolet absorbance at 280 nm (an indicator for aromaticity) and the E4:E6 ratio (an indicator for molecular weight) had additional effects on log K_DOC. The results indicate that the partitioning of pyrene to DOM is reduced at alkaline pH, probably due to the increased polarity of the organic macromolecules resulting from the deprotonation of functional groups. Only within a narrow pH range was the K_DOC of pyrene mainly related to the aromaticity of DOM.     

Sorption and desorption characteristics of organic phosphates of different structures on aluminium (oxyhydr)oxides

Sorption and desorption characteristics of four organic phosphates (OPs) with different molecular sizes and structures (glycerophosphate, GP; glucose‐6‐phosphate, G6P; adenosine triphosphate, ATP; myo‐inositol hexakisphosphate, IHP) and inorganic phosphate (P_i) on three aluminium (Al) (oxyhydr)oxides (amorphous Al(OH)₃, boehmite and α‐Al₂O₃) were investigated. The maximum sorption amounts of OPs and P_i increased with decreasing crystallinity of the minerals on a per mass basis: α‐Al₂O₃ < boehmite < amorphous Al(OH)₃. With an exception of IHP sorption on amorphous Al(OH)₃, the maximum surface area‐based sorption densities increased with decreasing molecular weight (MW) of OPs and P_i: IHP < ATP < G6P < GP < P_i. Despite having the largest MW, IHP had greater sorption amounts on amorphous Al(OH)₃ than the other OPs because of the transformation of surface complexes to surface precipitates. Sorption kinetics of OPs was first a rapid sorption followed by a long and slow sorption process. Of the three Al (oxyhydr)oxides, amorphous Al(OH)₃ had the greatest first rapid sorption density and initial sorption rate of OPs within 5 minutes, both factors decreasing with increasing MW of OPs. The initial desorption percentages of OPs by KCl generally increased with decreasing MW of OPs, whereas the maximum desorption percentages of OPs by citrate were four to five times those achieved with KCl. Overall, strong specific sorption of OPs occurs on the surface of Al (oxyhydr)oxides, and molecular structure and size of OPs, as well as crystallinity and crystal structure of the minerals, are the key factors affecting the interfacial reactions and environmental behaviour of OPs.     

Phosphorus exchange properties of European soils and sediments derived from them

The sorption and desorption of phosphorus (P) from eroding soil particles in land runoff are important processes contributing to agriculturally‐driven eutrophication. We investigated the P‐exchange properties and related chemical characteristics of contrasting European agricultural soils and sediment material eroded from them under indoor (small‐scale) and outdoor (larger‐scale) rainfall simulations. Quantity‐intensity (Q/I) relationships revealed large variation in equilibrium P concentrations at zero net P sorption (EPC₀) (0–10.3 mg l⁻¹) and instantly labile P (−Q₀, the amount of P to be desorbed to obtain a P equilibrium concentration of 0 mg l⁻¹) (2–75 mg kg⁻¹), both correlating closely with Al‐bound P and the P saturation degree of Al oxides (DPS_Alox). Maximum P sorption (Q_max) (43–515 mg kg⁻¹) also correlated most closely with Al_ox. The indoor and outdoor rainfall simulations produced sediments with different P sorption properties: in the indoor simulation (less kinetic energy, constant slope), the sediments had larger EPC₀ values, and usually larger −Q₀ values, than the sediments in the outdoor simulation (greater kinetic energy, variable slopes). Furthermore, the P exchange properties of the sediments differed from those of the bulk soil depending on the enrichment of soil P‐sorption components (Fe/Al oxides, clay). The outdoor simulation indicated that sites with gentle slopes produced sediments that were more enriched with Al_ox, Fe_ox, Mn_ox and organic C than those with steeper slopes. In this study, when the bulk soil had an initial EPC₀ greater than 1.3 mg l⁻¹, the outdoor rainfall simulation produced sediment with smaller EPC₀ and vice versa, indicating that, depending on the P status of the bulk soil, the sediment material was acting as source or sink for P during transport. However, on the basis of their EPC₀ values, most eroding sediments might be expected to desorb, rather than adsorb, P when entering surface water.