Enhanced soil washing of phenanthrene by mixed solutions of TX100 and SDBS

Increased desorption of hydrophobic organic compounds (HOCs) from soils and sediments is a key to the remediation of contaminated soils and groundwater. In this study, phenanthrene desorption from a contaminated soil by mixed solutions of a nonionic surfactant(octylphenol polyethoxylate, TX100) and an anionic surfactant (sodium dodecylbenzenesulfonate, SDBS) was investigated. Phenanthrene desorption depended on not only aqueous surfactant concentrations and phenanthrene solubility enhancement but also the soil-sorbed surfactant amount and the corresponding sorption capacity of sorbed surfactants. The added surfactant critical desorption concentrations (CDCs) for phenanthrene from soil depended on both sorbed concentrations of surfactants and their critical micelle concentrations (CMCs). Phenanthrene desorption by mixed solutions was more efficient than individual surfactants due to the low sorption loss of mixed surfactants to soil. Among the tested surfactant systems, mixed TX100 and SDBS with a 1:9 mass ratio exhibited the highest phenanthrene desorption. Mixed micelle formation, showing negative deviation of CMCs from the ones predicted by the ideal mixing theory, was primarily responsible for the significant reduction of soil-sorbed amounts of TX100 and SDBS in their mixed systems. Therefore, mixed anionic-nonionic surfactants had great potential in the area of enhanced soil and groundwater remediation.     

Interactions of organic contaminants with mineral-adsorbed surfactants

Sorption of organic contaminants (phenol, p-nitrophenol, and naphthalene) to natural solids (soils and bentonite) with and without myristylpyridinium bromide (MPB) cationic surfactant was studied to provide novel insightto interactions of contaminants with the mineral-adsorbed surfactant. Contaminant sorption coefficients with mineral-adsorbed surfactants, Kss, show a strong dependence on surfactant loading in the solid. At low surfactant levels, the Kss values increased with increasing sorbed surfactant mass, reached a maximum, and then decreased with increasing surfactant loading. The Kss values for contaminants were always higher than respective partition coefficients with surfactant micelles (Kmc) and natural organic matter (Koc). At examined MPB concentrations in water the three organic contaminants showed little solubility enhancement by MPB. At low sorbed-surfactant levels, the resulting mineral-adsorbed surfactant via the cation-exchange process appears to form a thin organic film, which effectively "adsorbs" the contaminants, resulting in very high Kss values. At high surfactant levels, the sorbed surfactant on minerals appears to form a bulklike medium that behaves essentially as a partition phase (rather than an adsorptive surface), with the resulting Kss being significantly decreased and less dependent on the MPB loading. The results provide a reference to the use of surfactants for remediation of contaminated soils/sediments or groundwater in engineered surfactant-enhanced washing.     

Particle-size dependent sorption and desorption of pesticides within a water-soil-nonionic surfactant system

Although nonionic surfactants have been considered in surfactant-aided soil washing systems, there is little information on the particle-size dependence of these processes, and this may have significant implications for the design of these systems. In this study, Triton-100 (TX) was selected to study its effect on the sorption and desorption of two pesticides (Atrazine and Diuron) from different primary soil size fractions (clay, silt, and sand fractions) under equilibrium sorption and sequential desorption. Soil properties, TX sorption, and pesticide sorption and desorption all exhibited significant particle-size dependence. The cation exchange capacity (CEC) of the bulk soils and the soil fractions determined TX sorption capacity, which in turn determined the desorption efficiency. Desorption of pesticide out of the clay raction is the limiting factor in a surfactant-aided washing system. The solubilization efficiency of the individual surfactant micelles decreased as the amount of surfactant added to the systems increased. Thus, instead of attempting to wash the bulk soil, a better strategy might be to either (1) use only the amount of surfactant that is sufficient to clean the coarse fraction, then separate the fine fraction, and dispose or treat it separately, or (2) to separate the coarse fractions mechanically and then treatthe coarse and fine fractions separately. These results may be applicable to many other hydrophobic organic compounds such as polyaromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs) strongly sorbed onto soils and sediments.     

Sorption behavior of nonylphenol in terrestrial soils

Nonylphenol (NP) as an intermediate from anaerobic degradation of widely used nonionic surfactants occurs widespread in the environment. Partition behavior of this toxic and endocrine-disrupting chemical between soil and water was not examined until yet. The objective of this investigation was to quantify sorption and desorption behavior of 4-nonyl[14C]phenol in a set of 51 soils using the batch equilibrium approach. Kinetic studies indicated apparent equilibrium within 20 h. Sorption was influenced by sorbate structure as could be shown with branched 4-nonyl[14C]phenol and the linear 4-n-NP, respectively. Linear 4-n-NP behaves differently from the branched isomers of 4-NP. Sorption of 4-nonyl[14C]phenol tested with five different initial concentrations resulted in linearly fitted isotherms that provided calculation of sorption partition coefficients (KP). Desorption partition coefficients (KP-des) revealed hysteresis independent of soil properties but decreasing with decreasing initial NP concentrations. KP values were correlated with organic carbon content of the soils yielding a log KOC of 3.97.     

Evaluation of component characteristics of soil-surfactant-herbicide system that affect enhanced desorption of linuron and atrazine preadsorbed by soils

The aim of the present work was to evaluate the surfactant-enhanced desorption of atrazine and linuron preadsorbed by soils and to study the effect of different characteristics of the components of soil-surfactant-herbicide systems on the efficiency of desorption. Two soils with organic matter contents of 3.16% and 7.28% and 11 surfactants, three of them anionic (SDS, LAS, and SDOSS) and 8 of them nonionic (Tween 80, Tween 20, Triton X-100, Triton X-114, Brij 35, Brij 30, Tergitol NP-10, and Tergitol 15S12), at concentrations 1.5 and 10 times the critical micellar concentration (cmc) were used. Adsorption-desorption studies were performed using a batch system, and the Freundlich model was applied to the isotherms except for some cases in which this was not possible. The desorption isotherms of both pesticides in aqueous medium pointed to the existence of hysteresis. The values of the hysteresis coefficients of the adsorption isotherms in water decreased in some cases while in others they increased in the presence of the surfactants, depending on the structure of these and on their concentration in water, on the organic matter content of the soil, and on the K(ow) of the herbicide. Parallel to the decrease in hysteresis, the percentage of herbicide desorption and desorption efficiency coefficient (E; ratio between the percentages of herbicide desorption in the presence of surfactant and those found in aqueous medium) increased. For a 10 cmc surfactant concentration, a linear relationship was seen between the E values and the absolute values of the cmc of the surfactants. Also, for the same surfactant, a linear relationship was seen between log E and the log of the absolute concentrations of surfactant in solution. The results obtained are of practical interest for the choice of surfactants for concrete problems involved in the recovery of pesticide-polluted waters using the surfactant-enhanced desorption pumping technique.     

Multiscale assessment of methylarsenic reactivity in soil. 1. Sorption and desorption on soils

Methylated forms of arsenic (As), monomethylarsenate (MMA), and dimethylarsenate (DMA) have historically been used as herbicides and pesticides. Because of their large application to agriculture fields and the toxicity of MMA and DMA, the persistency of these compounds in the environment is of great concern. MMA and DMA sorption and desorption were investigated in soils, varying in mineralogical and organic matter (OM) contents. Sorption studies showed that the MMA sorption capacity and rate were greater than DMA sorption. Al/Fe-oxyhydroxides were the main sorbents in the soils, and the sorption capacity was proportional to the Al/Fe concentration in the soils. Extended X-ray absorption fine structure (EXAFS) studies showed that both MMA/DMA-Fe interatomic distances were around 3.3 ?, which were indicative of bidentate binuclear inner-sphere complex formation. Desorption studies showed that not all of the sorbed MMA or DMA was desorbed due to the strong binding between MMA/DMA and Al/Fe-oxyhydroxide surfaces via possible inner-sphere complex formation. The amount of the desorbed MMA and DMA decreased as the sorption residence time increased. For example, 77% of sorbed MMA was desorbed from the Reybold subsoil after 1 day residence time, while 66% of sorbed MMA was desorbed from the soil after six months of residence time. The decreases in desorption were likely due to As speciation changes from MMA/DMA to inorganic arsenate, which was more strongly bound to the surface.     

Sorption and degradation of octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine in soil

The sorption/desorption and long-term fate of octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) was examined using sterilized and nonsterilized soils. Two soils were used that differ mainly by the amount of total organic carbon (TOC): an agricultural topsoil (VT, 8.4% TOC) and a sandy soil (SSL, 0.33% TOC). The adsorption isotherms performed at room temperature were well-described by a linear model, which led to sorption distribution coefficients of 2.5 and 0.7 L kg(-1) for VT and SSL soils, respectively. The organic content of soil did not significantly affect HMX sorption. Over a period of 20 weeks, HMX degraded (60% disappearance) in static anaerobic nonsterile VT soil preparations. In separate experiments using UL-[14C]-HMX, 19% mineralization (liberated 14CO2) was obtained in 30 weeks. In addition, four nitroso derivatives of HMX were detected. Knowing the sorption/desorption behavior and the long-term fate of HMX in soil will help assess the effectiveness of natural attenuation for HMX removal.     

Sorption of oxytetracycline to iron oxides and iron oxide-rich soils

The sorption interactions of oxytetracycline with goethite, hematite, and two iron oxide-rich soils were investigated using batch sorption experiments. Oxytetracycline sorption coefficients for goethite and hematite increased with pH to maximum values at pH approximately 8. The sorption edge shape and desorption treatments were consistent with a surface complexation mechanism and could be described by the interaction of divalent anion species with the oxide surface. Oxytetracycline sorption to Georgeville and Orangeburg Ultisol soils decreased with pH. Chemical digestion treatments were used to deduce that soil sorption occurred by complexation to oxide coatings on clay and quartz grains. These results indicate that sorption models must consider the interaction of oxytetracycline, and other similar ionogenic compounds, with soil oxide components in addition to clays and organic matter when predicting sorption in whole soils.     

Sorption equilibrium of a wide spectrum of organic vapors in Leonardite humic acid: experimental setup and experimental data

The environmental fate of volatile and semivolatile organic compounds is determined by their partitioning between air and soil constituents, in particular soil organic matter (SOM). While there are many studies on the partitioning of nonpolar compounds between water and SOM, data on sorption of polar compounds and data for sorption from the gas phase are rather limited. In this study, Leonardite humic acid/air partition coefficients for 188 polar and nonpolar organic compounds at temperatures between 5 and 75 degrees C and relative humidities between < 0.01% and 98% have been determined using a dynamic flow-through technique. To the best of our knowledge, this is by far the largest and most diverse and consistent data set for sorption into humic material published so far. The major results are as follows: the relative humidity affected the experimental partition coefficients by up to a factor of 3; polar compounds generally sorbed more strongly than nonpolar compounds due to H-bonding (electron donor/ acceptor interactions) with the humic acid; no glass transitions in the range of 5-75 degrees C that would be relevant with respect to the sorption behavior of hydrated Leonardite humic acid were observed; our experimental data agree well with experimental partition coefficients from various literature sources.     

The sorption of iodide by soils as influenced by equilibrium conditions and soil properties

The sorption of iodide was reduced when soil was dried before equilibration with an iodide solution. With undried soils, sorption continued for > 48 h, maximum sorption occurred at pH values < 5 but a secondary sorption peak occurred at pH 8.5 to 9.0, particularly with a soil containing a high level of organic matter. Temperature had only a small effect on sorption over the range 10 to 35 °C. Maximum values for the sorption of iodide by two surface soils (0 to 10cm) at pH 6.6 to 6.8, assessed with a soil: solution ratio of 1:10, an equilibrium time of 40 h and at room temperature, were 25 and 6 fig I/g soil, respectively. The amounts of iodide sorbed by these soils, and by soils taken from successive 10 cm layers to a depth of 40 cm at the same two sites, were closely related to the contents of organic matter in the soils but not to contents of iron or aluminium oxides or of clay. Treatment of the surface soils with hydrogen peroxide to destroy organic matter greatly reduced the sorption of iodide at the pH of about 5.5 that resulted from the treatment. The removal of iron and aluminium oxides with Tamm reagent also resulted in a marked reduction in sorption at pH < 5. The results indicate that sorption was due in part to soil organic matter and in part to iron and/or aluminium oxides. At pH > 6, organic matter appeared to be the major sorbing constituent but under more acid conditions the oxides appeared to be increasingly important.     

Modeling kinetics of Cu and Zn release from soils

Kinetics of Cu and Zn release from soil particles was studied using two surface soils with a stirred-flow method. Different solution pH, dissolved organic matter (DOM) concentrations, and flow rates were tested in this study. A model for kinetics controlled sorption/desorption reactions between soils and solutions was globally fit to all experimental data simultaneously. Results were compared to a model that assumes local instantaneous equilibrium. We obtained one unique set of model parameters applicable to different pH, dissolved organic carbon (DOC), and flow conditions. We included DOM complexation of copper ions, which decreased their sorption. The effect of pH was included by assuming proton competition with metal ions for binding sites on soil particles. These results provide the basis for developing predictive models for metal release from soil particles to surface waters and soil solution.     

The influence of natural organic matter rigidity on the sorption, desorption, and competitive displacement rates of 1,2-dichlorobenzene

The influence of natural organic matter (NOM) rigidity on the sorption, desorption, and competitive displacement rates of 1,2-Dichlorobenzene (1,2-DCB) was evaluated using batch reactor experiments with two surface soils (Yolo and Forbes) and a shale (Ohio). Previous characterization suggests that the shale NOM is the most reduced and condensed, the Yolo soil is the most oxidized and amorphous, and Forbes soil has an intermediate NOM structure. The rate study for each sorbent was conducted under the same reactor parameters, and 1,2-DCB mass-transfer rates were determined using the distributed first-order mass-transfer rate model based on the gamma probability density function. To measure competitive displacement rates, 1,2,4-trichlorobenzene (1,2,4-TCB) was delivered as a competitor after 34 days pre-equilibration. Higher fractions of contaminant subject to instantaneous mass transfer and much faster rates of approach to apparent sorption equilibrium are found in Yolo soil when compared with Forbes soil and the shale. The size of the instantaneously desorbing fraction thus appears inversely related to the hard carbon fraction. In the NOM compartment where mass transfer is rate-limited, rate coefficient distributions are shifted toward lower rates for desorption and competitive displacement of 1,2-DCB in Ohio shale, followed by Forbes soil. Sorption and desorption rate distributions are almost the same for the shale, while desorption rates are a few times greater than sorption rates in Yolo and Forbes soils. Mass-transfer coefficients for competitive displacement are considerably slower than those for desorption in Forbes soil and the shale. However, the mass-transfer rates for the two processes seem to be similar in Yolo soil, which has a NOM matrix comprising a relatively larger soft organic carbon fraction. The concept of "solute induced softening" is discussed as a mechanistic rationale for the experimental observations.     

Fate and transport of testosterone in agricultural soils

Hormones excreted in animal waste have been measured in surface and groundwater associated with manure that is applied to the land surface. Limited studies have been done on the fate and transport of androgenic hormones in soils. In this study, batch and column experiments were used to identify the fate and transport of radiolabeled [14C] testosterone in agricultural soils. The batch results indicated that aqueous-phase concentrations decreased for the first 5 h and then appeared to increase through time. The first-order sorption kinetics ranged from 0.08 to 0.640 h(-1) for the first 5 h. Beyond 5 h the increase in aqueous 14C could have been caused by desorption of testosterone back into the aqueous phase. However, metabolites were also produced beyond 5 h and would have likely resulted in the increase in aqueous 14C by sorption site competition and/or by lower sorption affinity. There were weak correlations of sorption with soil particle size, organic matter, and specific surface area. Testosterone was the dominant compound present in the soil column effluents, and a fully kinetic-sorption, chemical nonequilibrium model was used to describe the data. Column experiment sorption estimates were lower than the batch, which resulted from rate-limiting sorption due to the advective transport. The column degradation coefficients (0.404-0.600 h(-1)) were generally higher than values reported in the literature for 17beta-estradiol. Although it was found that testosterone degraded more readily than 17beta-estradiol, it appeared to have a greater potential to migrate in the soil because it was not as strongly sorbed. This study underlined the importance of the simultaneous transformation and sorption processes in the transport of hormones through soils.     

Effect of fluorotelomer alcohol chain length on aqueous solubility and sorption by soils

Fluorotelomer alcohols (FTOHs) are a group of polyfluorinated alkyl chemicals that have been widely studied as precursorsto perfluorocarboxylates such as perfluorooctanoic acid and for which knowledge on their fate in soils is sparse. The solubility and sorption by soil of the homologous 4:2 to 10:2 FTOHs were measured in water or cosolvent/ water solutions. For the smaller 4:2 and 6:2 FTOHs, solubility and sorption could be measured adequately in aqueous systems although transformation was apparent even in gamma-irradiated and autoclaved systems. Sorption coefficients estimated by measuring both sorbed and solution-phase concentrations were not significantly affected by the biotransformation process. The use of cosolvents was employed for probing the behavior of the longer-chain FTOHs with limited aqueous solubility. A single log-linear correlation between aqueous solubility and modified McGowan molar volumes resulted for the n-alkanols and FTOHs. Soil organic carbon (OC) consistently appeared to be the key soil property influencing sorption of the FTOHs while the perfluorocarbon chain length was the dominant structural feature influencing solubility and sorption. Each CF2 moiety decreased the aqueous solubility by -0.78 log units (compared to 0.60 log units for each CH2 addition in hydrogenated primary alcohols), and increased OC-normalized sorption coefficients (Koc) by -0.87 log units. Good log-log linear correlations between Koc and both octanol-water partition coefficients and solubility were observed for the FTOHs.     

Variation in phenanthrene sorption coefficients with soil organic matter fractionation: the result of structure or conformation?

Sorption of phenanthrene to varying soil types was investigated to better understand sorption processes. Humic acid and humin fractions were isolated from each soil sample, and sorption coefficients were measured by batch equilibration. Samples were characterized by carbon analysis and 13C cross polarization magic angle spinning (CP/ MAS) nuclear magnetic resonance (NMR) spectroscopy. Measured organic carbon-normalized sorption coefficients (Koc) of the fractions were greater in all cases when compared to the soils. The humin fractions exhibited greater Koc values than did source samples, suggesting that fractionation may reorganize organic matter in humin resulting in an increased availability of and/or more favorable sorption domains. Mass balance calculations revealed that the sum of sorption to the fractions is greater than sorption to the whole sample. The greatest difference between sorption values was found to occur with the mineral soils, suggesting that clay minerals influence the physical conformation of soil organic matter (SOM) and availability of sorption domains. The mass balance, sorption data, and a lack of consistent trends between observed Kco values and solid-state 13C NMR data suggest that the physical conformation of SOM and chemical characteristics both play important roles in sorption processes.     

The nature of soil organic matter affects sorption of pesticides. 1. Relationships with carbon chemistry as determined by 13C CPMAS NMR spectroscopy

The structural composition of soil organic matter (SOM) was determined in twenty-seven soils with different vegetation from several ecological zones of Australia and Pakistan using solid-state CPMAS 13C NMR. The SOM was characterized using carbon types derived from the NMR spectra. Relationships were determined between Koc (sorption per unit organic C) of carbaryl(1-naphthylmethylcarbamate) and phosalone (S-6-chloro-2,3-dihydro-2-oxobenzoxazol-3-ylmethyl O,O-diethyl phosphorodithioate) and the nature of organic matter in the soils. Substantial variations were revealed in the structural composition of organic matter in the soils studied. The variations in Koc values of the pesticides observed for the soils could be explained only when variations in the aromatic components of SOM were taken into consideration. The highly significant positive correlations of aromaticity of SOM and Koc values of carbaryl and phosalone revealed that the aromatic component of SOM is a good predictor of a soil's ability to bind such nonionic pesticides.     

Sorption and dissipation of testosterone, estrogens, and their primary transformation products in soils and sediment

Concern over the potential negative ecological effects of steroid hormones from human- and animal-derived wastes has resulted in an increased interest regarding the mobility and persistence of these compounds in the environment. Batch experiments were conducted to examine the simultaneous sorption and dissipation of three reproductive hormones (testosterone, 17beta-estradiol, and 17alpha-ethynyl estradiol) in four midwestern U.S. soils and one freshwater sediment. Sorption isotherms were generated by measuring aqueous concentrations and by extracting the sorbed parent chemical or transformation products (e.g., estrone, androstenedione). Apparent sorption equilibrium is reached within a few hours. Measured sorption isotherms for the three parent chemicals and their principal transformation products were generally linear. Average organic carbon normalized sorption coefficients (K(oc)) resulted in standard deviations of less than 0.2 log units and were consistent with reported aqueous solubilites and octanol-water partition coefficients, indicating hydrophobic partitioning as the dominant sorption mechanism. Large log K(oc) values (approximately 3-4) suggest that leaching from soils will be limited, runoff of soil- and land-applied biosolids are the most likely inputs into surface waters, and that a significant fraction of these compounds will be associated with sediments. Half-lives for hormone dissipation in the aerobic soil and sediment slurries estimated assuming pseudo first-order processes ranged from a few hours to a few days with testosterone having the shortest half-life.     

Freely dissolved concentrations of PAHs in soil pore water: measurements via solid-phase extraction and consequences for soil tests

Freely dissolved pore water concentrations are difficult to assess in complex matrixes such as soils or sediments. In this study, a negligible-depletion partitioning-based sampling technique was applied to measure freely dissolved pore water concentrations. A poly(dimethylsiloxane) (PDMS)-coated glass fiber was exposed to a slurry of a soil spiked with several PAHs at concentrations ranging from 2 to 2000 mg/kg. PAH-concentrations in the PDMS coating increased linearly with the total soil concentration until a certain maximum was reached. Freely dissolved pore water concentrations were calculated using PDMS-water partition coefficients, and the calculated maximum pore water concentrations corresponded with the aqueous solubility of the tested compounds. Furthermore, the sampling technique is very sensitive because it can detect freely dissolved pore water concentrations in the ng/L range for the tested PAHs. Freely dissolved pore water concentrations are an important parameter for the exposure of organisms in soil. Saturation of the pore water with increasing soil concentrations should therefore be considered in soil toxicity testing. Sorption coefficients that were calculated from freely dissolved concentrations were slightly higher than estimates based on octanol-water partition coefficients. These differences are discussed in relation to the effects of dissolved organic matter in soil pore water on the determination of sorption coefficients.     

Assessing sequestration of selected polycyclic aromatic hydrocarbons by use of adsorption modeling and temperature-programmed desorption

Sequestration of phenanthrene and pyrene was investigated in two soils--a sandy soil designated SBS and a silt-loam designated LHS--by combining long-term batch sorption studies with thermal desorption and pyrolysis of amended soil samples. The Polanyi-based adsorption volume and the adsorbed solute mass increased with aging for both soils, thus demonstrating the mechanism for observed sequestration. Despite rigorous thermal analysis, 30-62% (SBS sand) and 8-30% (LHS silt-loam) of phenanthrene could not be recovered after 30-270 days of sorption, with the increase in desorption resistance showing greater significance in SBS sand. For both soils, these values were 20-65% of adsorbed phenanthrene mass. Activation energies estimated from the temperature-programmed desorption (TPD) of sorbed phenanthrene at < or = 375 degrees C were 51-53 kJ/mol, consistent with values derived for desorption of organic compounds from humic materials. The activated first-order model fitting of observed TPD data supports the conclusion that the desorption-resistant fraction of phenanthrene has become sequestered onto condensed organic domains and requires temperatures exceeding 600 degrees C to be released. The work demonstrates the use of thermal analysis in complementing the Polanyi-based adsorption modeling approach for assessing the mechanistic basis for sequestration of organic contaminants in soils.     

Sorption-desorption of ionogenic compounds at the mineral-water interface: study of metal oxide-rich soils and pure-phase minerals

Sorption of the ionic compounds 2,4-D and quinmerac onto iron oxide-rich, variable charged soils was strongly influenced by mineralogy, particularly soil iron and aluminum oxides, whereas sorption of the neutral norflurazon was only related to total soil C. An appreciable fraction of the mass sorbed in stirred-flow studies was easily desorbed by deionized water, and desorption of ionic compounds was initially more rapid than sorption. This sorption-desorption behavior, although contrary to desorption hysteresis commonly observed in batch studies, suggests that the reversibly sorbed fraction is weakly bound to the soil surface. 2,4-D sorption to iron oxide-rich soils and pure-phase metal oxides appears to be driven by nonspecific electrostatic attraction, with specific electrostatic attraction and van der Waals interactions being secondary. Both the carboxylate and the heterocyclic N groups may participate in sorption of quinmerac, facilitated by specific and nonspecific electrostatic attraction and surface complexation. The heterocyclic N, amine, and carbonyl groups of norflurazon do not appear to interact with soil minerals.