A novel system for reducing leaching from formulations of anionic herbicides: clay-liposomes

A new approach was developed for reducing leaching of herbicides and contamination of groundwater. Liposome-clay formulations of the anionic herbicides sulfometuron and sulfosulfuron were designed for slow release by incorporating the herbicide in positively charged vesicles of didodecyldimethylammonium (DDAB), which were adsorbed on the negatively charged clay, montmorillonite. Freeze fracture electron microscopy demonstrated the existence of DDAB vesicles and aggregated structures on external clay surfaces. X-ray diffraction results for DDAB with montmorillonite imply the existence of DDAB bilayers with an oblique orientation to the basal plane within the clay interlayer space at adsorbed amounts beyond the cation exchange capacity of the clay. Adding DDAB with sulfometuron or sulfosulfuron to montmorillonite yielded 95% or 83% adsorption of the herbicide at optimal ratios. Liposome-clay formulations exhibited slow release of the herbicides in water. Analytical measurements in soil columns demonstrated 2-10-fold reduction in leaching of the herbicides from liposome-clay formulations in comparison with commercial formulations. Percents of root growth inhibition of a test plant in the upper soil depths were severalfold higher for the liposome-clay formulations than for the commercial ones. Consequently, liposome-clay formulations of anionic herbicides can solve environmental and economical problems by reducing their leaching.     

Environmentally friendly slow release formulations of alachlor based on clay-phosphatidylcholine

A new clay-liposome complex was developed for reducing leaching of herbicides and contamination of groundwater. The liposomes were composed of the neutral and Environmental Protection Agency approved phospholipid phosphatidylcholine (PC). Adsorption of PC liposomes on the clay mineral montmorillonite could exceed the cation exchange capacity of the clay, and was well simulated by the Langmuir equation. X-ray diffraction results for 6 mM PC and 1.6 g/L clay (3 day incubation) yielded a basal spacing of 7.49 nm, which was interpreted as the formation of a supported planar bilayer on montmorillonite platelets. Fluorescence methods demonstrated structural changes which reflected adsorption of PC followed by loss of vesicle integrity as measured by the penetration of dithionite into the internal monolayer of fluorescently labeled liposomes, resulting in a decrease in fluorescence intensity to 18% of initial after 4 h. Energy transfer was demonstrated after 1 h from labeled liposomes to montmorillonite labeled by an acceptor. The neutral herbicide alachlor adsorbed on the liposome-clay complex, yielding a formulation of up to 40% active ingredient, and 1.6-fold reduction in herbicide release in comparison to the commercial formulation. Hence, the PC-montmorillonite complex can form a basis for environmentally friendly formulations of herbicides, which would yield reduced leaching.     

Physico-chemical aspects of the vaailability of pesticides in soil. II. Controlled release of pesticides from granular formulations

The extent to which formulation factors control the release of a toxicant from granular formulations, under the leaching action of rain, has been investigated. Using granules prepared by an agglomeration process and containing the herbicide chlorthiamid, the rate of release can be varied by changing the filler base and by the use of different binding agents. By varying the binding agent a considerable degree of control can be exercised over the release of chlorthiamid. The release of toxicant is partly by direct leaching from the granule and partly by disintegration of the granule in water which renders the toxicant more accessible. The extent to which the release of other toxicants may be controlled in a similar way has been examined using ‘Bidrin’, fenuron, 2,4-D, chlorfenvinphos and N-tritylmorpholine. Toxicant release appeared to be governed by the filler/binding agent combination used in the granule and by the water solubility of the toxicant. Where the toxicant solubility is high, control over release is difficult to achieve but where the solubility is below 2000 ppm, a considerable control is possible.     

Persistence of herbicides in soil

A survey has been made of some of the physical, chemical and biological interactions that influence the persistence and availability of herbicides applied to the soil. The most important physical interaction between herbicides and soil is considered to be sorption of the pesticide to the soil surface. This influences not only the rate of leaching of the herbicide through the soil and its movement in the vapour phase, but also the rate of chemical and microbial decomposition. An attempt has been made to construct a model for the persistence of some hydrolytically sensitive herbicides to enable their persistence in soils to be deduced from hydrolysis rate-constants and adsorption data. The formulation used and the method of application of the herbicide to the soil can also have an important influence on its persistence.     

Trace metal leaching behavior studied through the use of parametric modeling of water borne soil particles fractionated with a split-flow thin cell

Leaching of particle-bound metals affects the ability of settling ponds and other engineered structures to remove metallic pollutants, and leaching behavior is related to particle size. In this investigation, water borne soil particles were leached and fractionated with a split-flow thin cell, and the metal loadings were quantified as a function of particle size. For comparison of the metal-loading curves, different empirical modeling procedures were investigated to convert the data to a precise functional form suitable for quantitative comparison of changes in differential loading as a function of particle size. Results of this investigation are presented for a soil sample before and after leaching caused by simulated acid rain conditions. Following simulated acid rain leaching, the shape of the differential distribution curves change, and these changes reflect the particle size mediated leaching behavior. For the soil used in this demonstration, simulated acid rain leaching shifted the differential loading toward larger particle sizes, and the magnitude of the shift varied significantly among the metals. Because settling rate decreases as the square of particle size, this could potentially affect management decisions for settling ponds receiving these particles. The high precision afforded by the analysis allows the development of insight into the leaching mechanisms through comparing "partial" acid rain leaching with "total recoverable" leaching by EPA Method 3050.     

2,4-D sorption in iron oxide-rich soils: role of soil phosphate and exchangeable Al

This study examined herbicide retention in iron oxide-rich variable charge soils (Ultisols) under no cultivation (forest), agriculture (farm), and turf maintenance (golf course) to explore the following hypothesis: inorganic phosphate accumulation from soil fertilization and liming to decrease exchangeable aluminum (Al) content will influence carboxylic acid herbicide sorption onto soils and leaching into groundwater. A suite of soil properties, including mineralogy (particularly soil iron and aluminum oxide content), exchangeable Al content, and soil phosphate content, influenced sorption of the anionic, 2,4-D. In general, 2,4-D sorption was lower in the presence of phosphate, possibly due to competition between phosphate and 2,4-D for surface sites or increase in surface negative charge resulting from phosphate sorption. Additionally, 2,4-D sorption was greater in the presence of exchangeable Al. It appears that 2,4-D may form surface complexes with or be electrostatically attracted to exchangeable aluminum in the soil. Our results suggest that carboxylic acid herbicides may be more easily leached in intensively managed Ultisols subject to continued phosphate fertilization and liming.     

Clay as a Carrier in Starch Encapsulated Herbicides Prepared by Extrusion Processing

Metolachlor and atrazine herbicides were separately incorporated into matrices containing all starch, all clay, and starch/clay blends by a twin-screw extrusion process. A low-cost clay and unmodified corn-starch were preblended dry, processed with water and herbicide in the extruder at 70–95°C, and extruded at 65% solids using an intense mixing screw. The extrudates were dried, milled, sieved (14-20 and 20-40 mesh), and analyzed for level of entrapped herbicide. The effect of various levels of clay and other variables on encapsulation efficiency, swellability, and release rates of the products in water were determined. The study showed that clay in the preblends of up to 50% had rather small effects on encapsulation efficiency and release rates of the products in water. As little as 20% starch in the blends remarkably slowed the release rates compared to that of clay alone. Processing the clay, herbicide and water without starch in the extruder significantly slowed the release rate compared to an unprocessed mixture of clay, metolachlor, and water. In all cases metolachlor was released more quickly than atrazine from the products (10-27% active ingredient).     

Physico-chemical aspects of the availability of pesticides in the soil. I.—Leaching of Pesticides from Granular Formulations

The way in which a pesticide is leached from a granular formulation differs from the way in which it is leached from a spray or dust formulation. This difference arises because granular applications do not provide the uniformity of coverage of the soil surface attainable with applications of finely divided sprays and dusts. This means that, besides the climatic factors such as temperature and quantity and intensity of rainfall that affect leaching, with granular formulations the distribution of granules over the soil is equally important. Thus the quantity of pesticide applied, the granule size, the pesticide content of the granules and their density may all affect the rate at which a pesticide is leached from the formulation. The inter-relation between these factors has been considered theoretically and the theoretical conclusions have been tested using granules prepared by agglomeration and containing the herbicide ‘Prefix’ (2,6-dichlorothiobenzamide). The effect of solubility of the pesticide in water has been studied using various pesticides having a range of water solubilities. As expected, the results show that the rate at which the pesticide is leached depends upon its solubility, but that the extent to which the granules break down under the influence of water can also be important.     

Configurations of the bentonite-sorbed myristylpyridinium cation and their influences on the uptake of organic compounds

Variations in the configuration of a sorbed myristylpyridinium (MP+) surfactant cation with a loading level in bentonite were examined by X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR); the attractive force from the clay basal surfaces to the sorbed MP+ and water molecule in the interlayers was estimated by thermogravimetric analysis (TG-DTG). At low loading levels (i.e., < CEC), MP+ sorbed mainly by cation exchange to clay basal surfaces to form tightly-adhered "organic films" (i.e., flat-layer). With increasing MP+ loading, sorbed MP+ gradually changed into a less confined "phase-like medium" (i.e., paraffin-type structures) via London attraction forces. Attractive forces between the mineral basal surfaces and the sorbed MP+ varied with the interlayer spacing and the stacking of MP+. Sorption of phenol and naphthalene to the resultant MP(+)--clay was a function of the configuration of MP+ aggregates on clay surfaces. At low MP+ densities, the sorbed MP+ film acted as an effective adsorbent for organic compounds. The carbon-normalized solute distribution coefficients (K(sf)) were exceptionally large and increased with MP+ densities up to approximately 340 (phenol) and approximattely 15000 mL g(-1) (naphthalene). At high MP+ loadings, the MP+ aggregates transformed into a partition-like medium, and the K(sf) values decreased sharply and leveled off. Nonetheless, because of the enhanced MP+ packing density within the clay interlayer, the solute K(sf) with a confined sorbed MP+ phase exceeded the corresponding aqueous micelle-water partition coefficients (k(mc)).     

High resolution electron microscopy structural studies of organo-clay nanocomposites

Engineering of clay nanocomposite materials by modification of their surfaces can enable the control of retention, transport, and persistence of toxic chemicals in the geosystem. The properties and interactions of clay nanocomposites have been widely studied, but little information exists on their microstructure at a range of scale extending down to atomic dimensions. The pairing of Na-montmorillonite clay with organic cations as well as with the herbicide fluridone, chosen as a model for an organic pollutant, was studied. Three organic cations were selected: hexadecyltrimethylammonium, benzyltrimethylammonium, and benzyltriethylammonium at 0%, 60%, and 100% of cation exchange capacity (CEC) loadings. A detailed microstructural analysis of the organo-clay nanocomposites and of the fluridone nanocomposites was undertaken by high-resolution transmission electron microscopy (HRTEM) and X-ray energy-dispersive spectroscopy (EDS). Morphological observations and chemical analyses were performed simultaneously on the same sample. The combined HRTEM and EDS measurements strongly suggest (a) heterogeneous local intercalation of the organic cations manifested by a range in the measured d001 spacing, implying random expansion of the clay layered structure with increased loading of the organic cations; (b) intercalation within the external layers, which is thoroughly influenced by local defect microstructure and/or edge availability of the montmorillonite nanoparticles as well as by the molecular structure of the intercalating organic cation. Additional intercalation of fluridone molecules did not affect the structure (d001 spacing) of the organo-clay nanocomposites.     

Percutaneous absorption of 4-cyanophenol from freshly contaminated soil in vitro: effects of soil loading and contamination concentration

Despite the skin's excellent barrier function, dermal exposure to soil contaminated with toxic chemicals can represent a significant health hazard (e.g., via multiple work related contacts in the farming and waste disposal industries). The development of environmental standards or limits for chemical levels in soil has been impeded because quantification of percutaneous uptake from this medium has not been well-defined. The objective of the research described here, therefore, was to better characterize the rate and extent of dermal penetration as a function of soil loading and degree of soil contamination. The absorption of a model compound (4-cyanophenol, CP) across hairless mouse skin in vitro has been determined at four different soil loadings (5, 11, 38 and 148 mg cm-2) and at six levels of soil contamination (concentrations ranging from 0.19 to 38 mg/g soil). Following 8 h of exposure, the amount of CP absorbed was independent of soil loading when CP concentration was constant, implying that the quantity of soil presentwas always sufficientto provide atleast a single layer of tightly packed particles. At the lowest loadings, however, with increasing times of exposure, the CP transport rate fell off due to depletion of chemical from the soil. At constant soil loading (38 mg cm(-2)), CP flux (Jss) across the skin was linearly proportional to the level of contamination (C(o)soil) over the range 0.19 to 23.5 mg of CP per gram of soil: Jss (micorg cm(-2) h(-1)) = (1.1 x 10(-5) g cm(-2) h(-1)) x Csoil (microg/g soil). At the highest CP contamination concentration, however, the transport rate was about an order of magnitude higher than expected, possibly due to the presence of pure CP crystals. In conclusion, these results provide new quantifications of the characteristics of dermal uptake from chemically contaminated soils and important information with which to develop and verify predictive models of dermal absorption.     

Proton buffering and metal leaching in sandy soils

Recent developments in acidification research focused on the leaching of metals from contaminated soil. In this paper the buffering of sandy soils upon acidification is studied in relation to the release of major (Al, Ca, Mg) and trace metals (Cu, Cd, Ni, Zn) from the soil reactive surface. The buffering process and the (de)sorption of metals are described with a mechanistic multisurface model, expressing the sorption onto different soil surfaces (organic matter, clay, Fe (hydr)oxides). The pH of sandy soil samples is predicted upon proton addition in combination with the behavior of major and trace metals. Acidification of contaminated sandy soil samples, with different pH levels and metal contents, is performed in a flow-through reactor by flushing the samples with acid solution. Acidification has taken place in successive steps of proton addition and followed by sampling. Prediction of pH upon acidification with a multisurface model gives satisfying results for all samples studied. The pH is modeled reasonably well between pH 6 and 4. Below pH 4 the predicted pH values are slightly too low, probably due to the buffering by Al-containing minerals (e.g., Al hydroxide), which are not included in the model. Desorption of major and trace metals upon pH decrease is, in general, predicted well, within a factor of 1-5 on a linear scale. Overall prediction of proton buffering in combination with desorption of metals in sandy soil samples, over a wide pH range and metal content, is done quite well for the studied metals with the multisurface model.     

Influence of copper loading and surface coverage on the reactivity of granular iron toward 1,1,1-trichloroethane

Although iron-based bimetallic reductants offer promise in treating organohalides, the influence of additive mass loading and two-dimensional surface coverage on reductant reactivity has not been fully elucidated. In this study we examine 1,1,1-trichloroethane reduction by Cu/Fe bimetals as a function of Cu loading and surface coverage. Information from a suite of complementary techniques (X-ray photoelectron spectroscopy, Auger electron spectroscopy, and cross-sectional energy-dispersive X-ray spectroscopy) indicates that displacement plating produces a heterogeneous metallic copper overlayer on iron. The dependence of pseudo-first-order rate constants (k(obs) values) for 1,1,1-trichloroethane reduction on Cu loading exhibits two distinct regimes. At Cu loadings less than 1 monolayer equivalent (approximately 10 micromol Cu/g Fe), a pronounced increase in k(obs) is associated with a corresponding increase in the two-dimensional surface coverage of Cu. A weaker dependence of k(obs) on Cu mass is exhibited at loadings in excess of 1 monolayer equivalent, which we ascribe to an increase in the volume of the metallic overlayer. The observed relationship between k(oba) and loading suggests that 1,1,1-trichloroethane reduction occurs on the Cu surface rather than at the interface between the Cu overlayer and the iron substrate.     

Analysis of crops and soils for residues of 2,6=dichlorobenzonitrile (dichlobenil) and 2,6=dichlorothiobenzamide (chlorthiamid). II.—Results

Crops and soils from a large number of field trials have been analysed for residues of 2,6dichlorothiobenzamide (chlorthiamid) and for residues of 2,6-dichlorobenzonitrile (dichlobenil). The thiobenzamide is converted to the benzonitrile after application to the soil and only a small percentage of the material applied initially remains unchanged after 4 weeks. However, both the benzonitrile and the thiobenzamide are of similar low mammalian toxicity. The initial half-life of the ‘total nitrile’ residues (the thiobenzarnide + the benzonitrile) is, on average, near 4 weeks but varies from 1 to 12 weeks depending on the locality, soil type, climate, dosage level and formulation. The penetration of the herbicide into soils of different types is considered and it is shown that in sand, loam, and clay, residues in the 4–12 in. layer are less than 10% of the residue at the same time in the 0–4 in. layer. Residues of the thiobenzamide and the benzonitrile could not be detected in a very wide range of crops (other than rice) harvested at 2–6 months after soil applications of the thiobenzamide at 1–16 lb/acre. In rice grains, where the plants can be in intimate contact with the herbicide, the ‘total nitrile’ residues did not exceed 0·05 ppm.     

Occurrence and fate of perfluorochemicals in soil following the land application of municipal biosolids

The recent implementation of soil and drinking water screening guidance values for two perfluorochemicals (PFCs), perfluorooctanoate (PFOA) and perfluorooctane sulfonate (PFOS) by the U.S. Environmental Protection Agency (EPA), reflects the growing concerns regarding the presence of these persistent and bioaccumulative chemicals in the natural environment. Previous work has established the potential risk to the environment from the land application of industrially contaminated biosolids, but studies focusing on environmental risk from land application of typical municipal biosolids are lacking. Thus, the present study investigated the occurrence and fate of PFCs from land-applied municipal biosolids by evaluating the levels, mass balance, desorption, and transport of PFCs in soils receiving application of municipal biosolids at various loading rates. This study is the first to report levels of PFCs in agricultural soils amended with typical municipal biosolids. PFOS was the dominant PFC in both biosolids (80-219 ng/g) and biosolids-amended soil (2-483 ng/g). Concentrations of all PFCs in soil increased linearly with increasing biosolids loading rate. These data were used to develop a model for predicting PFC soil concentrations in soils amended with typical municipal biosolids using cumulative biosolids loading rates. Mass balance calculations comparing PFCs applied vs those recovered in the surface soil interval indicated the potential transformation of PFC precursors. Laboratory desorption experiments indicated that the leaching potential of PFCs decreases with increasing chain length and that previously derived organic-carbon normalized partition coefficients may not be accurate predictors of the desorption of long-chain PFCs from biosolids-amended soils. Trace levels of PFCs were also detected in soil cores from biosolids-amended soils to depths of 120 cm, suggesting potential movement of these compounds within the soil profile over time and confirming the higher transport potential for short-chain PFCs in soils amended with municipal biosolids.     

Preparation of iron-loaded alginate gel beads and their release characteristics under simulated gastrointestinal conditions

The formulation and processing variables affecting the preparation of iron-loaded alginate beads for potential use as controlled release carriers were studied. The effect of alginates with different mannuronic/guluronic acid ratios, calcium concentration, loading of iron (II) and iron (III) compounds, variable iron loading times and incorporation of iron at different stages in the preparation were considered. Two successful strategies for the incorporation of iron into alginate beads involved using a mixed iron/calcium cross-linking bath or taking preformed calcium cross-linked beads and subsequently loading them with iron. Beads with 50–80 mg iron/g dried bead could be made with ferrous gluconate, high guluronic acid alginate and the mixed cross-linking bath method. Beads with higher loading, up to 180 mg iron/g dried bead, could be made by loading ammonium ferric citrate. Under simulated gastrointestinal conditions the beads progressively released iron in nutritionally relevant amounts.     

Slow formation and dissolution of Zn precipitates in soil: a combined column-transport and XAFS study

Recent spectroscopic studies have demonstrated the formation of layered double hydroxides (LDH) and phyllosilicates upon sorption of Zn2+, Ni2+, and Co2+ to clay minerals and aluminum oxides at neutral to alkaline pH and at relatively high initial metal concentrations (>1 mM). The intention of the present study was to investigate whether such phases also form in soil under slightly acidic conditions and at lower metal concentrations. Columns packed with a loamy soil were percolated with aqueous solutions containing 0.1 or 0.2 mM Zn, Ni, Co, and Cd in a 10 mM CaCl2 background at pH 6.5. Metal breakthrough curves indicated a rapid initial sorption step, resulting in retarded breakthrough fronts, followed by further slow metal retention during the entire loading period of 42 days (7000 pore volumes). Total metal sorption and the contribution of slow sorption processes decreased in the order Zn > Ni > Co > Cd. Leaching the reacted soil with 10 mM CaCl2 at pH 6.5 remobilized 8% of the total retained Zn, 15% of Ni, 21% of Co, and 77% of Cd. Subsequent leaching with acidified influent (pH 3.0) remobilized most of the remaining metals. X-ray absorption fine-structure (XAFS) spectroscopy revealed that slow Zn sorption was due to the formation of a Zn-Al LDH precipitate. Although Ni, Co, and Cd concentrations were too low for XAFS analysis, their leaching patterns suggest that part of Ni and Co were also incorporated in solid phases, while most sorbed Cd was still present as exchangeable sorption complex after 42 days. A small but significant percentage of the sorbed metals (2-5%) remained in the soil, even after leaching with more than 3000 pore volumes at pH 3.0, which may suggest micropore diffusion or incorporation into more stable mineral phases.     

A WHAM-based kinetics model for Zn adsorption and desorption to soils

A novel model has been developed to describe the kinetics of Zn adsorption and desorption to soils. The model incorporates the mechanistic-based equilibrium model WHAM (Windermere humic aqueous model) to account for the chemical variation during the reaction (e.g., pH and Zn2+ concentration), the heterogeneity of binding sites of soil organic matter (SOM), and the nonlinear binding of Zn to SOM. To test the model, kinetic experiments were conducted using a stirred-flow method. Six soils, with low clay fractions and covering a wide range in SOM concentrations, and various Zn concentrations and pHs were studied. Under these experimental conditions, SOM is found to be the major adsorbent for Zn binding. The fast and slow Zn reactions with soils were associated, respectively, with the monodentate and bidentate binding sites of humic substances in WHAM. The model has only three fitting parameters, the two desorption rate coefficients for the fast (monodentate) and slow (bidentate) reaction sites which are constant and independent of soil type, and the reactive organic matter fraction of the total SOM in each soil. All other parameters are derived from WHAM. The model is able to predict Zn release from spiked soils including the effects of Ca competition.     

Sorption and conformational characteristics of reconstituted plant cuticular waxes on montmorillonite

Plant cuticular waxes are essential barriers that regulate the transport of water and organic molecules to intact cuticular membranes. They also compose a significant fraction ofthe recalcitrant aliphatic components of soil organic matter (SOM). In this study, we examined the sorption and desorption of three polycyclic aromatic hydrocarbons (PAHs), naphthalene (NAPH), phenanthrene (PHEN), and pyrene (PYR), by cuticular waxes of green pepper (Capsicum annuum) that had been reconstituted by loading them onto montmorillonite (at four different loadings). The reconstituted wax samples, with and without sorbed PAHs, were characterized by solid-state 13C NMR to supply the evidence of melting transition. The sorption isotherms fit well to a Freundlich equation. Sorption isotherms were practically linear except for that of PYR sorption to the low-load wax-montmorillonite sample. The organic-carbon-normalized sorption coefficients (Koc) depended on PAH's lipophilicity (e.g., octanol-water partition coefficient) and increased with increasing wax-load on clay. Desorption was dependent on PAH's molecular sizes and sorbed amounts and on the wax load of the clay. Desorption hysteresis was observed only at high loads of NAPH and PHEN, and it decreased with both increasing wax load and molecular size (i.e. NAPH > PHEN > PYR). Contributing to hysteresis, the melting transition of the reconstituted waxes after sorbing the PAHs was confirmed by solid-state 13C NMR data. Upon adsorption, the intensity of the NMR peak at 29 ppm (attributed to mobile amorphous paraffinic domains) increased, and a peak at 167 ppm (-COOH) appeared, reflecting the transition of solid amorphous to mobile amorphous domains in the reconstituted waxes. The intensity of melting induced by PAH adsorption decreased with increasing PAH molecular size.     

Relative effects of surfactants and humidity on soil/air desorption of chloroacetanilide and dinitroaniline herbicides

Herbicides are typically applied as formulation mixtures in order to ensure uniform application and improve biocide performance, but little is known about the effects of formulated surfactants on herbicide exchange between soil and the atmosphere. Desorption experiments were performed for seven herbicides from the chloroacetanilide and dinitroaniline families with model anionic-nonionic surfactant mixtures under a range of relative humidity (RH) conditions (3-66%) on two soils. Enhanced desorption of herbicides from soil to the gas phase was observed asthe concentration of surfactant mixture or the RH increased. Multiple linear regression models developed to summarize the soil/air desorption behavior of these herbicides revealed that surfactant concentration, relative humidity, and herbicide properties (i.e., K(H), K(OA)) all have significant contributions to herbicide desorption. However, the ANOVA results indicated that surfactant concentration only accounted for 1.4% of the variance in desorption, RH accounted for 40-60%, and herbicide properties, logK(H) or logK(OA), accounted for 20-40%. The study results predict that less than a 20% increase (study range 1.5-21.0%) in surfactant concentration could double the atmospheric losses of herbicide from their soil application sites, and about a 60% increase in ambient RH (3-66%) elevated the losses by 10-40 times.