Sorption of 2,4-D and other phenoxy herbicides to soil, organic matter, and minerals

Purpose

We review 2,4-dichlorophenoxyacetic acid (2,4-D) and other phenoxy herbicide sorption experiments.

Methods

A database with 469 soil–water distribution coefficients K _d (in liters per kilogram) was compiled: 271 coefficients are for the phenoxy herbicide 2,4-D, 9 for 4-(2,4-dichlorophenoxy)butyric acid, 18 for 2-(2,4-dichlorophenoxy)propanoic acid, 109 for 2-methyl-4-chlorophenoxyacetic acid, 5 for 4-(4-chloro-2-methylphenoxy)butanoic acid, and 57 for 2-(4-chloro-2-methylphenoxy)propanoic acid. The following parameters characterizing the soils, solutions, or experimental procedures used in the studies were also compiled if available: solution CaCl₂ concentration, pH, pre-equilibration time, temperature, soil organic carbon content (f _oc), percent sand, silt and clay, oxalate extractable aluminum, oxalate extractable iron (Oxalate Fe), dithionite–citrate–bicarbonate extractable aluminum, dithionite–citrate–bicarbonate extractable iron (DCB Fe), point of zero negative charge, anion exchange capacity, cation exchange capacity, soil type, soil horizon or depth of sampling, and geographic location. K _d data were also compiled characterizing phenoxy herbicide sorption to the following well-defined sorbent materials: quartz, calcite, α-alumina, kaolinite, ferrihydrite, goethite, lepidocrocite, soil humic acid, Fluka humic acid, and Pahokee peat.

Results

The data review suggests that sorption of 2,4-D can be rationalized based on the soil parameters pH, f _oc, Oxalate Fe, and DCB Fe in combination with sorption coefficients measured independently for humic acids and ferrihydrite, and goethite.

Conclusions

Soil organic matter and iron oxides appear to be the most relevant sorbents for phenoxy herbicides. Unfortunately, few authors report Oxalate Fe and DCB Fe data.     

RHIZOSPHERE MICROBIAL POPULATIONS IN CONTAMINATED SOILS

Rhizosphere microbial populations may increase bioremediation of soil contaminated with organic chemicals. A growth chamber study was conducted to evaluate rhizosphere microbial populations in contaminated and non-contaminated soil. Alfalfa (Medicago sativa L.) and alpine bluegrass (Poa alpina L.) were grown in soil containing a mixture of organic chemicals for 14 weeks. The equal millimolar mixture of hexadecane, (2,2-dimethylpropyl)benzene, cis-decahydronaphthalene (decalin), benzoic acid, phenanthrene, and pyrene was added at levels of 0 and 2000 mg/kg. Organic chemical degrader (OCD) populations were assessed by a Most-Probable-Number technique, and bacteria and fungi were enumerated by plate count methods. Different methods for expressing OCD rhizosphere populations were investigated to determine the effect it had on interpretation of the results. At 9 weeks, the OCD numbers were significantly higher in rhizosphere and contaminated soils than in bulk and non-contaminated soils, respectively. Alfalfa rhizosphere OCD levels were 4 × 10⁷/g for contaminated and 6 × 10⁶/g for non-contaminated soils. Bluegrass rhizosphere OCD levels were 1 × 10⁷/g and 1 × 10⁶/g in contaminated and non-contaminated soils, respectively. Selective enrichment of OCD populations was observed in contaminated rhizosphere soil. Higher numbers of OCD in contaminated rhizospheres suggest potential stimulation of bioremediation around plant roots.     

Low-molecular weight organic acids improve plant availability of phosphorus in different textured calcareous soils

Understanding the role of organic acids on phosphorus (P) sorption capacity of soils is very important for its economic and friendly management. Combining P application with low-molecular weight organic acids could result in its higher plant availability for prolonged time. Therefore, citric and oxalic acid (at the rate of 1.0 mM kg^?1 soil) were evaluated for their effect on P sorption capacity and its plant availability in two different textured calcareous soils. Organic acids decreased P sorption capacity and organic carbon partition coefficient (K_oc) whereas increased Gibbs free energy (ΔG) of P. Organic-acid-treated soils required lesser quantity of P fertilizer to produce soil solution P concentration optimum for plant growth (external P requirement [EPR_0.2]), that is, 0.2 mg L^?1. Citric acid was efficient than oxalic acid in the above effects. P sorption parameters of Freundlich model were negatively correlated with lime potential and ΔG whereas had positive correlation (P < 0.05) with EPR_0.2 and K_oc. Incubation with oxalic acid increased available P in loamy sand and loam soil by 20% and 30%, respectively. Thus, organic acids could help reduce application rate of P fertilizer through lowering its adsorption in highly P-fixing soils without compromise on yield.     

Adsorption-desorption of trichloroethylene in granular media

Sorption studies were conducted to determine the adsorption and desorption characteristics of a common synthetic chemical, trichloroethylene (TCE) in four granular media; sandy loam soil, organic top soil, peat moss and granular activated carbon (GAC). The results showed that the Freundlich Isotherm satisfactorily represents adsorption and desorption of dissolved TCE in these media and that the organic carbon content is an important factor in both processes. The soil-water partition coefficient (K _oc) for TCE suggests that it will migrate quickly through soil.     

Biodegradation of PAHs and PCBs in Soils and Sludges

Results from a multi-year, pilot-scale land treatment project for PAHs and PCBs biodegradation were evaluated. A mathematical model, capable of describing sorption, sequestration, and biodegradation in soil/water systems, is applied to interpret the efficacy of a sequential active–passive biotreatment process of organic chemicals on remediation sites. To account for the recalcitrance of PAHs and PCBs in soils and sludges during long-term biotreatment, this model comprises a kinetic equation for organic chemical intraparticle sequestration process. Model responses were verified by comparison to measurements of biodegradation of PAHs and PCBs in land treatment units; a favorable match was found between them. Model simulations were performed to predict on-going biodegradation behavior of PAHs and PCBs in land treatment units. Simulation results indicate that complete biostabilization will be achieved when the concentration of reversibly sorbed chemical (S _RA) reduces to undetectable levels, with a certain amount of irreversibly sequestrated residual chemical (S _IA) remaining within the soil particle solid phase. The residual fraction (S _IA) tends to lose its original chemical and biological activity, and hence, is much less available, toxic, and mobile than the “free” compounds. Therefore, little or no PAHs and PCBs will leach from the treatment site and constitutes no threat to human health or the environment. Biotreatment of PAHs and PCBs can be terminated accordingly. Results from the pilot-scale testing data and model calculations also suggest that a significant fraction (10–30%) of high-molecular-weight PAHs and PCBs could be sequestrated and become unavailable for biodegradation. Bioavailability (large K _d , i.e., slow desorption rate) is the key factor limiting the PAHs degradation. However, both bioavailability and bioactivity (K in Monod kinetics, i.e., number of microbes, nutrients, and electron acceptor, etc.) regulate PCBs biodegradation. The sequential active–passive biotreatment can be a cost-effective approach for remediation of highly hydrophobic organic contaminants. The mathematical model proposed here would be useful in the design and operation of such organic chemical biodegradation processes on remediation sites.     

Phytotoxicity of some chloroanilines and chlorophenols, in relation to bioavailability in soil

Soil adsorption and the effect of four chlorophenols and three chloroanilines on the growth of lettuce (Lactuca sativa) were determined in two soil types differing in organic matter content and pH. Adsorption increased with increasing organic matter content of the soils. Phytotoxicity, based on dosed amounts, was significantly higher in the soil with the low level of organic matter. This difference could be reduced by recalculating the EC₅₀ values for the effect of the test substances on plant growth in mg kg-1 dry soil towards concentrations in mg L-1 pore water using data from soil adsorption experiments. For pentachlorophenol only this recalculation increased rather than decreased the difference between the two soils, however, when the EC50 values for pentachlorophenol were corrected for the difference in soil pH, almost the same values resulted for both soils. Calculated EC₅₀ values on the basis of pore water concentrations appeared to be in good agreement with values determined in nutrient solution tests. These results indicate that, for plants, the toxicity and therefore the bioavailability of organic chemicals in soil mainly depend on the concentration in the soil solution, and can be predicted on the basis of sorption data. Attempts to develop QSARs relating log EC₅₀ values in μmol L^?1 pore water with lipophilicity (expressed as the octanol/water partition coefficient: log K_ow,) of the test substances resulted in a statistically significant relationship. This relationship was further improved by correcting the chlorophenol data for dissociation effects.     

The Effect of the Organic Matter Composition on POP Accumulation in Soil

The effect of different humic fractions on polychlorinated biphenyl (PCB) contamination in soils was tested in the field by means of 53 soil samples from a high-altitude grassland plateau in the Italian Alps. Three humic fractions (humin, humic acids, and fulvic acids) were characterized in parallel by quantifying 12 PCB congeners to establish a direct relationship between PCB levels and humic fraction concentrations. Humin (the most hydrophobic fraction) appears to be the most closely correlated with the amount of PCBs in soil (R ²?=?0.83), while fulvic acid shows the lowest correlation (R ²?=?0.49). The idea of preferential sorption of hydrophobic compounds in the humin fraction is discussed, and the humin carbon content (f _huminC) is proposed as an improved parameter for evaluating the potential for POP accumulation in soils, replacing total organic carbon (f _oc). Congener studies revealed that penta- and hexa-substituted-CBs show the optimal combination of physicochemical properties for equilibrating with the humin content in soil. Moreover, f _huminC/f _oc is conceptually equivalent to the empirical coefficients used in predictive K _sa equations. In our samples, the f _huminC/f _oc was 0.55, a value in between the empirical coefficients proposed in the literature. In predictive equations, the use of f _huminC instead f _oc avoids the necessity of using an empirical parameter for a ??generic?? condition by introducing an experimental parameter (f _huminC) that takes into account local conditions (organic matter composition).     

Cadmium soil sorption at low concentrations: VIII. correlation with soil parameters

Cadmium distribution coefficients, K _d were determined at low Cd concentrations (solute: 0.2 to 3.0 μg Cd dm^?3, soil: 0.044 to 1.1 mg Cd kg^?1) for 63 Danish agricultural soils. The K _d values ranged from 15 to 2450 L kg^?1. About 40% of the soils had K _d values below 200 L kg^?1. The observed K _d values correlated very well with soil pH (r ² = 0.72). Introducing soil organic matter content as a second parameter improved the correlation some (r ² = 0.79). No further improvements were obtained by introducing traditional soil parameters as clay, silt, fine sand, coarse sand and CEC or ‘reactive’ parameters as oxyhydroxides of Mn, Fe and Al. The identified regression equation for predicting K _d values indicates that K _d approximately doubles for each 0.5 unit increase in pH or 2% increase (weight basis) in organic matter content.     

Conversion factor (k factor) for estimation of soil microbial biomass potassium by the chloroform-fumigation extraction method

The conversion factor, k_K, for estimation of microbial biomass potassium (K) by the chloroform-fumigation extraction method was determined for some arable soils: upland field soils under different fertilization conditions, an upland field soil under a greenhouse condition, and a paddy field soil under a flooded condition. The k_K value varied with land utilization (paddy or upland) or fertilization (chemical or organic fertilizer). Value of k_K was different between paddy field soil (0.28–0.38) and upland field soil (0.41–0.73). This study indicates that the value could be useful for the estimation of microbial biomass K in soil by the chloroform-fumigation extraction method and further investigation of the amounts of biomass K in different types of soils under conditions with varied field managements will be necessary.     

Partitioning of polycyclic aromatic hydrocarbons (PAH) to water-soluble soil organic matter

The mobility of polycyclic aromatic hydrocarbons (PAH) in soils can be influenced by the presence of dissolved organic matter. Partition coefficients of selected polycyclic aromatic hydrocarbons, ranging from 3-ring to 6-ring compounds, to water-soluble soil organic matter (WSSOM) were determined. Partition coefficients were determined for WSSOM obtained from two soils under agricultural use and forest and for commercially available humic acid (Aldrich), taking advantage of a reversed phase (C₁₈) separation method. The WSSOM was characterised with regard to charge and hydrophilic/hydrophobic properties with a dissolved organic matter (DOM) fractionation method. No sorption to WSSOM was found for the tri- and tetracyclic PAH, whereas the penta- and hexacyclic PAH showed a significant binding to both types of WSSOM and to Aldrich humic acid. The affinity of penta- and hexacyclic PAH to WSSOM was considerably lower compared to the affinity to Aldrich humic acid. This is suggested to be due to the lower amount of hydrophobic fractions, c. 30%, in the natural WSSOM as compared to Aldrich humic acid. Effective partition coefficients (Koc_eff) for the sorption of PAH to bulk soil calculated from K_DOC and DOM in the naturally occurring concentration range were only 60–70% of the K_oc values in pure water. The impact of DOM on pollutant transport is further influenced by non-equilibrium behaviour of PAH in soils and by sorption of DOM to the solid-soil matrix. Several scenarios are described in which the effect of DOM on pollutant transport may become important.     

Soil properties affecting solid–liquid distribution of As(V) in soils

The prediction of the mobility of arsenic (As) is crucial for predicting risks in soils contaminated with As. The objective of this study is to predict the distribution of As between solid and solution in soils based on soil properties and the fraction of As in soil that is reversibly adsorbed. We studied adsorption of As(V) in suspensions at radiotrace concentrations for 30 uncontaminated soils (pH 4.4–6.6). The solid–liquid distribution coefficient of As (K_d) varied from 14 to 4430 l kg^?1. The logarithm of the concentration of oxalate‐extractable Fe explained 63% of the variation in log K_d; by introducing the logarithm of the concentration of oxalate‐extractable P in the regression model, 85% of the variation in log K_d is explained. Double labelling experiments with ⁷³As(V) and ³²P(V) showed that the As to P adsorption selectivity coefficient decreased from 3.1 to 0.2 with increasing degree of P saturation of the amorphous oxides. The addition of As(V) (0–6 mmol kg^?1) reduced the K_d of ⁷³As up to 17‐fold, whereas corresponding additions of P(V) had smaller effects. These studies suggest that As(V) is adsorbed to amorphous oxides in soils and that sites of adsorption vary in their selectivity in respect of As and P. The concentration of isotopically exchangeable As in 27 contaminated soils (total As 13–1080 mg kg^?1) was between 1.2 and 19% (mean 8.2%) of its total concentration, illustrating that a major fraction of As is fixed. We propose a two‐site model of competitive As(V)–P(V) sorption in which amorphous Fe and Al oxides represent the site capacity and the isotopically exchangeable As represents the adsorbed phase. This model is fitted to ⁷³As adsorption data of uncontaminated soils and explains 69% of the variation of log K_d in these soils. The log K_d in contaminated soils predicted using this two‐site model correlated well with the observed log K_d (r = 0.75). We conclude that solubility of As is related to the available binding sites on amorphous oxides and to the fraction of As that is fixed.     

Sorption of s-Triazine Herbicides in Organic Matter Amended Soils: Fresh and Incubated Systems

Fresh amendment of soil with sewage sludge and composted sewage sludge resulted in increased sorption of three s-triazine herbicides: atrazine, ametryn and terbuthylazine. The extent of increased sorption (as evaluated by sorption coefficients K_d or K_f) was a function of soil type, such that sorption in amended organic carbon-poor soil (0.4% OC) was more enhanced than in amended organic carbon-rich soil (1.55% OC). Despite significant differences between the organic amendments in terms of humic and fulvic acid content, humin content, soluble organic matter content, total organic matter content, and H/C and O/C atomic ratios, organic matter composition had no discernible effect on either sorption distribution coefficients or on isotherm linearity in amended soils. Soils amended with composted sludge had the same sorption potential as did soils amended with the analogous uncomposted sludge. After incubating soil-sludge mixtures for a year at room temperature, organic matter content decreased to original pre-amendment levels. Sorption coefficients for the three compounds similarly decreased to initial pre-amendment values. Organic carbon normalized sorption coefficients (K_oc) were essentially identical in the soils, amended soils, and incubated amended soils, indicating that sludge and compost derived organic matter does not have a significantly different sorption capacity as compared with the original soils, despite compositional differences.     

Leaching of Terbuthylazine and Bromacil Through Field Soils

A field experiment was designed to provide data on the effect of soil heterogeneity on the distribution of herbicides following leaching by irrigation and rain water. Terbuthylazine and bromacil, two nonconservative herbicides, together with CaBr₂, a conservative chemical, were used in the reported experiment. The experimental field consisted of a noncultivated 175-m² plot in which 20 observation points were randomly selected. A hundred and ten centimeters of irrigation and rainwater were applied and the field was periodically sampled for chemical distributions. The spatial variability of the field was determined by measuring the K_s (saturated conductivity) and α (Gardner parameter). Auxiliary laboratory experiments were performed to define the adsorption-desorption of the chemicals studied in these field soils. Results on the adsorption-desorption of terbuthylazine and bromacil and on the redistribution of these chemicals in the field to a depth of 120 cm during leaching are shown. Bromacil leached to a greater extent than terbuthylazine. The differences among the concentrations of herbicides in the various cores studied may be explained in terms of properties of the chemicals and soil spatial variability. The residual concentrations of terbuthylazine and bromacil were also determined to a depth of 400 cm after the leaching of 110 cm of water. In some of the cores, two zones showing a relatively high concentration of terbuthylazine and bromacil were observed at depths of 40–60 and 200–300 cm, respectively. This redistribution pattern of the herbicides could be explained by the preferential flow of the solute in the cores studied.     

Bestimmung der Boden-Wasser-Verteilung leichtflüchtiger Kohlenwasserstoffe mittels Dampfraum-GC

Rapid Headspace-GC determination of the soil-water partition ratio of volatile hydrocarbons The hydrocarbon load of contaminated soils is usually mainly adsorbed to the soil organic matter. The laboratory determination of the sorption equilibration of volatiles suffers from severe drawbacks due to volatilization losses of the analytes and low recoveries if liquid extraction methods are applied. The presented headspace technique for the determination of partition coefficients produces reliable results, also under adsorptive as well as under desorptive conditions. It was shown that the volatiles tested are subject to rather severe ad-/desorption hysteresis which strengthens the necessity to determine the desorptive K_oc in contaminated sites. Additionally significant data were obtained that demonstrated a very strong effect of the organic matters quality on the partition ratios of volatiles.     

The molecular composition of soil organic matter as determined by 13C NMR and elemental analyses and correlation with pesticide sorption

Although the chemical composition of soil organic matter (SOM) is known to significantly influence sorption of pesticides and other pollutants, it has been difficult to determine the molecular nature of SOM in situ. Here, using ¹³C nuclear magnetic resonance (NMR) data and elemental composition in a molecular mixing model, we estimated the molecular components of SOM in 24 soils from various agro‐ecological regions. Substantial variations were revealed in the molecular nature of SOM. As a proportion of soil carbon the proportion of the carbonyl component ranged from 0.006 to 0.05, charcoal from 0 to 0.15, protein from 0.09 to 0.29, aliphatic from 0.14 to 0.30, carbohydrate from 0.21 to 0.31, and lignin from 0.05 to 0.42. The relationships between K_oc (sorption per unit mass of organic carbon) of carbaryl (1‐naphthyl methylcarbamate) and phosalone (S‐6‐chloro‐2,3‐dihydro‐2‐oxobenzoxazol‐3‐ylmethyl O,O‐diethyl phosphorodithioate) and the molecular nature of organic matter in the soils were significant. Of the molecular components estimated, lignin and charcoal contents correlated best with sorption of carbaryl and phosalone. Aliphatic, carbohydrate and protein contents were found to be negatively correlated with the K_oc of both pesticides. The study highlights the importance of the molecular nature of SOM in determining sorption affinities of non‐ionic pesticides and presents an indirect method for sorption estimation of pesticides.     

Partitioning of metals (Cd, Co, Cu, Ni, Pb, Zn) in soils: concepts, methodologies, prediction and applications – a review

Prediction of the fate of metals in soil requires knowledge of their solid–liquid partitioning. This paper reviews analytical methods and models for measuring or predicting the solid–liquid partitioning of metals in aerobic soils, and collates experimental data. The partitioning is often expressed with an empirical distribution coefficient or K_d, which gives the ratio of the concentration in the solid phase to that in the solution phase. The K_d value of a metal reflects the net effect of various reactions in the solid and liquid phases and varies by orders of magnitude among soils. The K_d value can be derived from the solid–liquid distribution of added metal or that of the soil‐borne metal. Only part of the solid‐phase metal is rapidly exchangeable with the solution phase. Various methods have been developed to quantify this ‘labile’ phase, and K_d values based on this phase often correlate better with soil properties than K_d values based on total concentration, and are more appropriate to express metal ion buffering in solute transport models. The in situ soil solution is the preferred solution phase for K_d determinations. Alternatively, water or dilute‐salt extracts can be used, but these may underestimate in situ concentrations of dissolved metals because of dilution of metal‐complexing ligands such as dissolved organic matter. Multi‐surface models and empirical models have been proposed to predict metal partitioning from soil properties. Though soil pH is the most important soil property determining the retention of the free metal ion, K_d values based on total dissolved metal in solution may show little pH dependence for metal ions that have strong affinity for dissolved organic matter. The K_d coefficient is used as an equilibrium constant in risk assessment models. However, slow dissociation of metal complexes in solution and slow exchange of metals between labile and non‐labile pools in the solid phase may invalidate this equilibrium assumption.     

Contribution of Soil Components on the Sorption of Chlorpyrifos

It is generally assumed that the sorption of a nonionic pesticide on soil depends mainly on the content of soil organic matter (SOM); however, there are other factors that can contribute to this process. The possible causes of variation in the carbon-normalized partition coefficient (K _OC) for chlorpyrifos (CPF) for a diverse set of ten soils have been investigated. On the one hand, the analysis of the chemical composition of the SOM was analyzed, and on the other hand, the likely interactions between the organic matter and the mineral phase were assessed. Sorption experiments of CPF were performed on whole soil, on soils treated with 2% hydrofluoric acid (HF), and onto calcined soil at 550 °C. Organic matter chemistry of soil was determined by ¹³C CP/MAS NMR spectroscopy; K _OC values were positively correlated with aryl C relative proportion and negatively correlated with alkyl C and O-aryl C proportions and prediction equation of K _OC was found (R ²?=?0.82, p?<?0.001). To evaluate possible organo-mineral interactions, a mathematical model was proposed which calculates the concentration of CPF at equilibrium (C _cal) considering adsorption coefficients for the organic (K _DHF) and inorganic (K _D550 °C) soil constituents, separately. The comparison between C _cal and the equilibrium concentration obtained from experimental data (C _exp) onto whole soil allowed us to confirm that interactions between the OM and clay affect the adsorption of CPF in whole soil. Such findings should be taken into account in the development of predictive models for the evaluation of the fate and transport of this pesticide in soil.     

Comparison of analytical procedures for determination of soil sorption coefficients of some triazine herbicides

Abstract

The sorption behavior of three triazine herbicides: atrazine, metribuzin, and terbutryn was studied in two different soils. Three experimental procedures to determine the K_f values were assayed: the conventional batch equilibration method in which the sorbed concentration is calculated by difference from the change in solution concentration; an alternative mass balance equilibrium batch technique in which the solution and the sorbed phase concentration are measured directly; and the flow equilibration method in which a solution of known concentration was passed through a column of soil until the effluent reached the same concentration as the input solution. Four concentrations of each herbicide were selected and results were fitted to the linearized form of the Freundlich isotherm. Recovery of the herbicides was studied in soil and water samples using the same four concentrations employed in the sorption assays. Average recoveries ranged from 86 to 104% with standard deviations lower than 10%. The K_oc (mg^1–1/n kg^‐1 L^l/n) values obtained ranged from 43 to 87 for atrazine, 27 to 114 for metribuzin, and 355 to 505 for terbutryn. The exponents 1/n of the Freundlich adsorption isotherms were lower than unity, with only one exception, and varied from 0.72 to 0.86 for atrazine, 0.73 to 1.12 for metribuzin, and 0.76 to 0.99 for terbutryn. The solution method gave values of K_oc that were 1.25, 1.55, and 2.65 (average of both soils) times those of the mass balance method for terbutryn, atrazine and metribuzin, respectively. When adsorption was low, the mass balance calculation method is recommended if the batch equilibration method is used, since the solution method can produce a considerable overestimation of adsorption. The flow equilibration method produced similar values of adsorption than the mass balance batch equilibration method and it made the experimental procedure easier since pesticide solution concentration need not to be measured once the equilibration time has been determined to ensure that the equilibrium was reached.     

Adsorption of the antibiotic pharmaceutical compound sulfapyridine by a long‐term differently fertilized loess Chernozem

Residues of antibiotic pharmaceutical compounds (APCs) found in the environment are suspected to be translocated into the food chain and to provoke the formation of resistant microorganisms. However, the behavior of APCs in soils is largely unknown. In the present study batch experiments were carried out with sulfapyridine (SPY) and p‐aminobenzoic acid (ABA) amended to two loess Chernozem samples. Due to different fertilization in the course of a long‐term field experiment samples differed substantially in the concentration of organic carbon (C_org 1.6 and 2.4%) and composition of soil organic matter (SOM). APCs in soil extracts were analyzed by high performance liquid chromatography. The K_F values of the Freundlich isotherm for SPY were 2.2 (1.6% C_org) and 5.5 (2.4% C_org). The K_oc values were 101 and 308. The different K_oc values indicated that not only the quantity but also the composition of SOM affected the SPY adsorption. Adsorption of SPY was substantially higher in moist than in air‐dry soil. ABA, consisting of a carboxyl group instead of the sulfonamide group substituted with a N‐heterocycle, was much less adsorbed than SPY (K_F 0.2). From this it was concluded that the N‐heterocycle significantly contributed to the adsorption of SPY.