Mobility Of Atrazine Research Articles

Transport of Atrazine in Residue-Amended Soils

In this study, our aim was to quantify the transport of atrazine in soil columns where sugarcane (Saccharum spp. hyb.) residue was incorporated. The residue is a result of sugarcane combine harvest technology where massive amount of residue is deposited on the soil surface after each harvest. Miscible displacement experiments were carried out to quantify the mobility of atrazine in soil columns where sugarcane residue was mixed a Commerce soil. The residue was either incorporated uniformly with the soil or applied as a thin mulch layer over surface soil. The incorporation of residue with the soil resulted in retarded atrazine mobility because of strong sorption and slow release of the breakthrough curves (BTCs) during leaching. Moreover, early arrival of atrazine in the column effluent was observed from BTC results where the residue was uniformly incorporated with the soil, which is possibly due to physical nonequilibrium conditions, that is, preferential flow or macropore flow. An equilibrium-type model was incapable of describing atrazine BTCs from all columns regardless of whether the residue was placed as a surface layer or incorporated in the soil. In contrast, good overall description of measured BTC results was realized when a fully kinetic model was used. Therefore, our hypothesis that kinetic rather than equilibrium-type reactions are the dominant mechanisms for the release of adsorbed atrazine from the residue is supported.

Atrazine sorption and fate in a Ultisol from humid tropical Brazil

This study combined laboratory based microcosm systems as well as field experiments to evaluate the mobility of atrazine on a Ultisol under humid tropical conditions in Brazil. Results from sorption experiments fit to the Freundlich isotherm model [K(f) 0.99 mg kg(-1)/(mg l(-1))(1/n)], and indicate a low sorption capacity for atrazine in this soil and consequently large potential for movement by leaching and runoff. Microcosm systems using (14)C-atrazine to trace the fate of the applied herbicide, showed that 0.33% of the atrazine was volatilized, 0.25% mineralized and 6.89% was recorded in the leachate. After 60 d in the microcosms, 75% of the (14)C remained in the upper 5 cm soil layer indicating atrazine or its metabolites remained close to the soil surface. In field experiments, after 60 d, only 5% of the atrazine applied was recovered in the upper soil layers. In the field experiments atrazine was detected at a depth of 50 cm indicating leaching. Simulating tropical rain in field experiments resulted in 2.1% loss of atrazine in runoff of which 0.5% was adsorbed onto transported soil particles and 1.6% was in solution. Atrazine runoff was greatest two days after herbicide application and decreased 10 fold after 15 d. The use of atrazine on Ultisols, in the humid tropics, constitutes a threat to water quality, causing surface water and ground water pollution.

Soil and Herbicide Properties Influenced Mobility of Atrazine, Metolachlor, and Primisulfuron‐Methyl in Field Lysimeters

Understanding herbicide mobility in soils is necessary to prevent groundwater contamination. We studied the mass balance distribution of three 14C‐labeled herbicides (atrazine, metolachlor, and primisulfuron‐methyl) in four soils (Dothan, Portsmouth, Rion, and Wagram) 128 d after application to soil column field lysimeters. Analyses were made of surface soil, subsoil, and leachate samples, and metabolites were identified in surface soil and leachate. Our objectives were to examine, measure, and correlate the leaching patterns of the chemicals and correlate their leaching characteristics with the physicochemical properties of the soils. Metolachlor was the most mobile herbicide as indicated by the retardation factor (Rf) (Rf = 0.35 in 1992 and 0.17 in 1993), followed by atrazine (Rf = 0.19 in 1992 and 0.09 in 1993) and primisulfuron‐methyl (Rf = 0.15 in 1992 and 0.12 in 1993). Herbicide mobility (Rf) was related to leachate volume collected from the four soils, herbicide aqueous solubility, and longevity of the chemicals. The herbicides were of greatest mobility in Rion and Wagram soils and of lowest mobility in Portsmouth and Dothan soils. Soil factors affected the weakly basic atrazine differently than the nonionizable metolachlor or the weakly acidic primisulfuron‐methyl. Volatility losses of the herbicides were inversely related to longevity (disappearance time in the field (DT50) of the compounds and to humic matter contents of the soils. Carbon‐14 herbicide in the subsoil and in the leachate was correlated with herbicide mobility (Rf), total leachate volume, and 50% disappearance time values. Herbicide mobility was in agreement with predictability using a simple decision‐aid model.

Sorption Kinetics and Equilibria of Organic Pesticides in Carbonatic Soils from South Florida

A batch reactor was used to determine sorption kinetic parameters (k2, F, and K*) and the equilibrium sorption coefficient (K). The two-site nonequilibrium (TSNE) batch sorption kinetics model was used to calculate the kinetic parameters. Two probe organic pesticides, atrazine [2-chloro-4-ethylamino-6-isopropylamino-s-triazine] and diuron [3-(3,4-dichlorophenyl)-1,1-dimethylurea] were studied using three carbonatic soils from South Florida (Chekika, Perrine, and Krome), one noncarbonatic soil from Iowa (Webster), and one organic soil (Lauderhill) from South Florida. Carbonatic soils contained more than 600 g kg(-1) CaCO3. Sorption is initially very fast up to 3 h and then slowly reaches equilibrium. All soil-chemical combinations reached sorption equilibrium after about 24 h and all sorption isotherms were linear. The sorption kinetics data were well described by the TSNE model for all soil-chemical combinations except for the marl soil data (Perrine-Atrazine), which were better described by the one-site nonequilibrium (OSNE) model. Diuron, with higher K, undergoes slower sorption kinetics than atrazine. The Lauderhill soil containing organic carbon (OC) of 450 g kg(-1) exhibited slowest sorption kinetics for both pesticides. An inverse relationship between k3 and K was observed for atrazine and diuron separately in Chekika, Webster, and Lauderhill soils but not in Perrine and Krome soils. The sorption kinetic parameters were used to distinguish the sorption behavior between atrazine and diuron and to identify differences between soils. Normalizing the sorption coefficient (K) to OC showed that atrazine and diuron had K oc values in carbonatic soils that were a third of reported literature values for noncarbonatic soils. Using existing literature K oc values in solute transport models will most likely underestimate the mobility of atrazine, diuron, and other neutral organic chemicals in carbonatic soils.

Predicting Pesticide Transport in Mulch‐Amended Soils

With adoption of combine harvest technology, massive sugarcane (Saccharum Spp. Hyb.) residue is left on the soil surface following each harvest, which could affect the environmental fate and efficacy of applied pesticides in subsequent cropping seasons. The objective of this study was to quantify the retention characteristics and mobility of a commonly used herbicide, atrazine (2‐chloro‐4‐ethylamine‐6‐isopropylamino‐S‐triazine), in soils when sugarcane mulch residue was present. Specifically, adsorption and desorption kinetic batch experiments were performed to quantify atrazine retention by the mulch residue over time. Atrazine sorption exhibited time‐dependent behavior and was followed by slow release regardless of input concentration. A kinetic—equilibrium model based on a second‐order two‐site (SOTS) formulation was successful in describing atrazine adsorption versus time by the mulch residue. One set of model parameters was capable of describing atrazine release based on six successive desorption steps. As a test for the applicability of the model, data sets from two other experiments where sorption and release was measured for extended time periods (1348 and 2476 h) were successfully predicted by the SOTS model. Miscible displacement methods were used to measure the mobility of atrazine in packed columns where the mulch residue was mixed with a reference sand material or a Sharkey clay soil (very fine, smectitic, thermic Chromic Epiaquerts). Use of batch‐measured model parameters did not adequately describe atrazine mobility in the sand‐mulch column. In contrast, for a Sharkey‐mulch soil column, a two‐compartment SOTS model was successful in predicting atrazine breakthrough results where independently estimated parameters for the mulch residue and the soil matrix were used as the input parameters. Results also showed that mixing of mulch with soil created physical non‐equilibrium condition in the columns, which was responsible for errors in model predictions.

TRANSPORT AND PERSISTENCE OF NITRATE, ATRAZINE, AND ALACHLOR IN LARGE INTACT SOIL COLUMNS UNDER TWO LEVELS OF MOISTURE CONTENT

The objective of this study was to determine the relative mobility and persistence of atrazine, alachlor, and nitrate (NO 3 - ) in soil columns at two levels of moisture content, high saturation (∼70%) and low saturation (∼40%). Large intact soil columns of (i) Naron fine sandy loam (fine, loamy, mixed, thermic Udic Argiustoll) and (ii) Pratt loamy fine sand (sandy, mixed, thermic Psammentic Haplustalf), were obtained from two sites in Kansas. Liquid flow was traced by bromide (Br - ), a relatively nonreactive chemical. Transport behavior of Br - and NO 3 - was comparable, i.e., concentrations of both solutes in leachates peaked at about the same pore volume (PV). In high moisture columns, concentrations of anions in effluents peaked after eluting 0.7 and 1.2 PV through the Naron and Pratt columns, respectively. Under low moisture conditions, Br - and NO 3 - effluent concentrations reached maxima after about 1 PV, and breakthrough curves (BTCs) were nearly symmetrical around the center of mass. Bromide recoveries were generally high (≥0.90 mg mg -1 applied) in both moisture regimes. Regardless of moisture regime, initial breakthrough of atrazine and alachlor in leachates occurred much later than did the anions, suggesting chemical interaction between herbicides and solid phase. Atrazine and alachlor BTCs showed tailing, an indication of possible nonequilibrium sorption. Degradation of atrazine to deethylatrazine and deisopropylatrazine was evident in low moisture soil columns, with deethylatrazine detected in greater concentrations. The order of mobility for the triazines was deethylatrazine > atrazine > deisopropylatrazine. Atrazine recovery was greater in high- than in low moisture columns, likely due to increased residence times conducive to biotic and/or abiotic transformation. Alachlor was less mobile and less persistent than atrazine. Recoveries of alachlor in high moisture columns were 0.130 and 0.098 mg mg -1 in Naron and Pratt soils, respectively. Alachlor was not detected in effluents of low moisture columns.

RELATIVE MOBILITY OF ATRAZINE, 2,4-D AND DICAMBA IN VOLCANIC SOILS OF SOUTH-CENTRAL CHILE 1

Herbicide mobility has been studied extensively in nonvolcanic soils but not in the volcanic soils that are important to the agricultural systems of many regions, including Pacific-Rim countries. Volcanic soils have unique properties that include high contents of organic carbon and soil water at 1500 kPa tension, low bulk density and saturation of bases, and the presence of amorphous clay. We hypothesized that the chemical and physical characteristics of these soils would affect the mobility of selected herbicides. Therefore, thin-layer chromatography was used to measure the relative mobility of atrazine, diethylamine salt of 2,4-D, and dicamba in volcanic soils of south-central Chile, including Arrayan silt loam (Typic Haploxerands), Santa Barbara silt loam (Typic Haploxerands), Arenales loamy sand (Dystric Xeropsamments), and weathered Collipulli clay loam (Xeric Palehumults) series. Dicamba was the most mobile herbicide in all of the soils; atrazine was the least mobile herbicide in the weathered Collipulli soil and in the surface horizons of the Arrayan and Arenales soils, but 2,4-D was the least mobile in the Santa Barbara soil. Herbicide mobility in the allophanic soils (Arrayan, Santa Barbara, and Arenales) could be estimated using the contents of soil organic matter and 1500 kPa water, and also soil pH. The relative mobility of atrazine was greater than expected in the Arrayan and Santa Barbara soils and was probably caused by the protonation and subsequent repulsion of atrazine by positively charged soil surfaces. The relative mobilities of 2,4-D and dicamba were smaller than expected in the Santa Barbara soil and were attributed to the retention of dissociated 2,4-D and dicamba by positively charged soil surfaces.

SURFACE EXCHANGE PHASE COMPOSITION AND NONIONIC SURFACTANT EFFECTS ON THE NONEQUILIBRIUM TRANSPORT OF ATRAZINE

Numerous studies have been reported regarding atrazine (2-chloro-4-isopropyl-6 ethyl-diamino-triazine) sorption/desorption and mobility in soil using the pure atrazine compound. Relatively little research has been carried out on atrazine behavior in soil minerals in the presence of surfactants. We hypothesized that clay mineralogy and surfactants may influence sorption/mobility of atrazine. In this study, we conducted miscible displacement experiments to elucidate the influence of the surfactant Brij 35 (C 12 H 25 [C 2 H 4 O] 23 OH), clay mineral type, and exchange phase composition on atrazine mobility in mixtures of specially prepared 2:1 clays. Chromatography columns were packed in duplicate with sand and Na- or Ca-saturated illite or mixtures of Na- or Ca-bentonite (0:1, 1:1, 9:1). The columns were presaturated with defined CaCl 2 (154 mmol C L -1 ) or CaCl 2 plus NaCl (SAR = 75 (mmol L -1 ) -1/2 ) solutions and adjusted to pH 6.3. Columns were later eluted with a pulse of a 6 mg L -1 atrazine solution with or without 0.1% Brij 35, incubated for 48 h after atrazine breakthrough, and then washed with d-H 2 O. Results showed that atrazine breakthrough was incomplete (max C/Co < 1.0) in all systems. In the bentonite systems, the atrazine breakthrough curve (BTC) in the presence of Brij 35 was shifted to the left of the atrazine BTC in the absence of Brij 35 (at one pore volume) when the Na- to Ca-bentonite ratio = 9:1, suggesting that the surfactant enhanced atrazine mobility. In contrast, surfactant was shown to reduce atrazine mobility with a diminishing Na- to Ca-bentonite ratio. Similar results were found in the illite systems, but in reverse order with respect to Na- and Ca-clay exchange phase composition. Based on our work, we concluded that the exchange phase composition impacted the surfactant's ability to mobilize atrazine in soils.

A field tracer study of attenuation of atrazine, hexazinone and procymidone in a pumice sand aquifer.

A field tracer experiment, simulating point source contamination, was conducted to investigate attenuation and transport of atrazine, hexazinone and procymidone in a volcanic pumice sand aquifer. Preliminary laboratory incubation tests were also carried out to determine degradation rates. Field transport of the pesticides was observed to the significant under non-equilibrium conditions. Therefore, a two-region/two-site non-equilibrium transport model, N3DADE, was used for analysis of the field data. A lump reduction rate constant was used in this paper to encompass all the irreversible reduction processes (e.g. degradation, irreversible adsorption, complexation and filtration for the pesticides adsorbed into particles and colloids) which are assumed to follow a first-order rate law. Results from the field experiment suggest that (a) hexazinone was the most mobile (retardation factor R = 1.4) and underwent least mass reduction; (b) procymidone was the least mobile (R = 9.26) and underwent the greatest mass reduction; (c) the mobility of atrazine (R = 4.45) was similar to that of rhodamine WT (R = 4.10). Hence, rhodamine WT can be used to delimit the appearance of atrazine in pumice sand groundwater. Results from the incubation tests suggest that (a) hexazinone was degraded only in the mixture of groundwater and aquifer material (degradation rate constant = 4.36 x 10(-3) day-1); (b) procymidone was degraded not only in the mixture of groundwater and aquifer material (rate constant = 1.12 x 10(-2) day-1) but also in the groundwater alone (rate constant = 2.79 x 10(-2) and-1); (c) atrazine was not degraded over 57 days incubation in either the mixture of aquifer material and groundwater or the groundwater alone. Degradation rates measured in the batch tests were much lower than the total reduction rates. This suggests that not only degradation but also other irreversible processes are important in attenuating pesticides under field conditions. Hence, the use of laboratory-determined degradation rates could underestimate reduction of pesticides in field conditions.

Mobility of atrazine from alginate-bentonite controlled release formulations in layered soil

The mobility of atrazine [6-chloro-N 2-ethyl-N 4-isopropyl-1,3,5-triazine-2,4-diamine] from alginate–bentonite-based controlled release (CR) formulations was investigated by using soil columns. Two CR formulations based on sodium alginate (14.0 g kg −1), atrazine (6.0 g kg −1), natural or acid-treated bentonite (50 g kg −1), and water (924 g kg −1) were compared to technical grade product and commercial liquid (CL) formulation (Gesaprim 500FW). All herbicide treatments were applied to duplicate layered bed systems simulating the typical arrangement under a plastic greenhouse, which is composed of sand (10 cm), peat (2 cm), amended soil (20 cm) and native soil (20 cm). The columns were leached with 39 cm (1500 ml) and 156 cm (6000 ml) of 0.02 M CaCl 2 solution to evaluate the effect of water volume applied on herbicide movement. When 39 cm of 0.02 M CaCl 2 solution was applied, there was no presence of herbicide in the leachate for the alginate–bentonite CR treatments. However, 0.11% and 0.14% of atrazine appeared in the leachate when the treatment was carried out with technical grade and CL formulations, respectively. When 156 cm of 0.02 M CaCl 2 solution was applied, the use of the alginate-acid treated bentonite CR formulation retards and reduces the presence of atrazine in the leachate as compared to technical product. Analysis of the soil columns showed the highest atrazine concentration in the peat layer. Alginate–bentonite CR formulations might be an efficient system for reducing atrazine leaching in layered soil and thus, it could reduce the risks of pollution of groundwater.

Analytical methods for the determination of alachlor, metolachlor, simazine and atrazine mobility in soils

A method for the determination of the mobility of the herbicides, alachlor, metolachlor, simazine and atrazine in soil is described . The method is based on the use of soil thin‐layer chromatography (TLC) and does not require the use of radiolabelled compounds. Soil on the TLC plate after development was separated into various bands, the material in each band was extracted with solvents and analyzed by gas chromatography.

The influence of manure on movement of Atrazine through Soil

In this research the effect of land application of manure on atrazine leaching was examined under laboratory conditions using 14C‐labelled compound. Four undisturbed and two disturbed soil columns, in replicates were used to study the effect of rate and time of manure application relative to rainfall on atrazine transport through saturated soil. Manure and atrazine were applied at a rate of 60m3/ha (6500 gal/acre) and 2.4 kg/ha, respectively. Application of manure increased the peak concentration and decreased the time to peak and mean time of elusion of atrazine in all soil columns. Atrazine mobility was faster when rainfall occurred immediately after manure application. In the disturbed soil columns, the average peak relative concentration of effluent (C/Co) without manure was 3.1% and occurred after the passage of about 2.2 pore volumes compared to C/Co of 6.9% and occurred at 1.2 pore volumes with manure. In one of the undisturbed soil columns, the peak concentration C/Co without manure was 47% and occurred after the passage of 0.07 pore volume. The corresponding C/Co in the presence of manure, when rainfall occurred immediately after manure application, was as high as 138% and occurred after only 0.03 pore volume.

EFFECT OF SUBIRRIGATION ON THE MOBILITY OF ATRAZINE

A three-year field lysimeter study was conducted to investigate the effect of water table management on themobility of applied atrazine in a sandy soil. The mobility of herbicide atrazine was examined under three water tablemanagement schemes: shallow subirrigation, deep subirrigation, and free drainage. Nine PVC lysimeters, 1.0 m long and0.45 m in diameter, were packed with sandy soil to a bulk density of 1350 kg/m3 and atrazine was applied to the soilsurface each summer at the rate of 2.4 kg/ha of active ingredient. Only water samples were collected in 1993 and 1994,but both water and soil were sampled and analyzed in 1995 at different time intervals. Atrazine was found to have leacheddown the soil profile, and its concentration level reduced with depth. The mass balance study showed a significantdifference in the dissipation of atrazine levels in the 0.4-m subirrigation treatment (shallow subirrigation treatment). Itdissipated more quickly under shallow subirrigation, and dissipation loss of around 96.5% were observed during thegrowing season of 1995. The contrast between the atrazine residues in the 0.4-m subirrigation versus 0.8-m subirrigationand free drainage treatment was statistically significant at the 95% level. Although relatively lower atrazine residues werefound in the 0.8 m subirrigation compared to the free drainage treatment, the contrast between them was not statisticallysignificant. This indicates that the most atrazine dissipation occurs at the soil root zone depths, and that only shallowsubirrigation could significantly reduce atrazine residues in this sandy soil by maintaining higher moisture content in thecrop root zone.

Sorption of atrazine and dicamba in Delaware coastal plain soils: a comparison of soil thin layer and batch equilibrium results

The mobility and retention of atrazine and dicamba in six Atlantic Coastal Plain soils were estimated by soil thin-layer chromatography (soil-TLC). The soils studied were representative of the major agricultural regions in Delaware and were sampled, by horizon, to the water table. Four horizons from each profile were leached simultaneously with distilled water on one soil-TLC plate. Two values were obtained from each plate: the ratio of the distance traveled by the herbicide center of mass over that traveled by the solvent front (Rm), and a sorption distribution coefficient (Kd). The Rm values ranged from 0·06 to 0·94 for atrazine and from 0·80 to 0·94 for dicamba. Herbicide mobility was found to be greatest in coarse-textured soil horizons that contained low levels of organic matter, clay, and Fe and Al oxides. Correlation analysis indicated that effective cation exchange capacity, exchangeable acidity, exchangeable aluminum, and clay were useful predictive variables or both atrazine mobility and sorption. Organic matter was not useful for predicting soil-TLC derived sorption estimates; however, it was correlated to Kd-batch estimates. Distribution coefficients calculated from soil-TLC data were found to be in general agreement with Kd values obtained for the same soils by batch equilibrium techniques. The average Kd-soil-TLC values for atrazine and dicamba were 2·09(±2·24) and 0·03(±0·02), respectively. The ratio of the batch Kd to the soil-TLC Kd ranged from 0·1 to 19 (x̄=1·6, SD=3·8) for atrazine and from 2·9 to 38 (x̄=12·6, SD=8·7) for dicamba. Thus, although for some horizons agreement between the two methods was good, for other horizons significant discrepancies existed. It is suggested that the soil-TLC gives results under non-equilibrium conditions, whereas the batch procedure is, by definition, at quasi-equilibrium. These fundamental differences may account for the observed differences between the two methods. It is also suggested that, due to this difference, the soil-TLC procedure can provide additional information relevant to herbicide partitioning in the field environment that is not provided by traditional batch equilibrium techniques. © 1998 Society of Chemical Industry

The influence of surfactants applied by sewage sludge on the behaviour of Atrazine and PAHs in semiarid soils

AbstractThe effect of two surfactants applied via sewage sludge: LAS (linear Alkylbenzenesulfonate) and Nonylphenol as a metabolite of Nonylphenol ethoxylate, on PAHs and Atrazine mobility was investigated under semiarid soil conditions in a Vertisol and a Gypsisol treated with sewage sludge. In both cases the surfactants promoted the leachability of Atrazine only moderately compared to the untreated plot. PAHs were leached from the surface layer (0–20 cm) into 20–50 cm layer during the three month test period. Relatively higher leaching was observed in the sandy Gypsisol. Atrazine was leached only in the clayrich Vertisol where the surfactants were present longer than in the plot with sandy Gypsisol.

Atrazine Adsorption by Soil Colloids and Co‐Transport through Subsurface Environments

AbstractThis study evaluated the potential of water‐dispersible soil colloids with diverse physicochemical and mineralogical characteristics to adsorb and mediate the transport of atrazine through macropores of intact soil columns. The soil columns were taken from the upper solum of an Alfisol (Maury) and a Mollisol (Loradale) in the Bluegrass region of Kentucky. Six different colloid suspensions mixed with atrazine [2‐chloro‐4‐(ethylamino)‐6‐(isopropylamino)‐s‐triazine] were introduced at a constant flux into the undisturbed soil columns. The eluents were collected and analyzed periodically for colloid and herbicide concentrations. Colloid recovery in the eluents ranged from 45 to 90%. The presence of colloids enhanced the transport of atrazine by 2 to 18%, depending on colloid type and mobility. Colloids with higher pH, total exchangeable bases (TEB), cation‐exchange capacity (CEC), organic carbon (OC), surface area (SA), and electrophoretic mobility (EM), showed greater mobility, greater affinity for atrazine, and greater potential to co‐transport atrazine. In contrast, increased levels of kaolinite, Fe, and Al inhibited atrazine adsorption and transport. Soil columns with higher hydraulic conductivity, well‐developed macropore system, and lower surface reactivity (Maury) also transported more atrazine. In spite of the increased transportability of atrazine by the presence of soil colloids, the colloid‐bound herbicide fraction contributed ≤1% to the observed increase. This suggests that matrix‐surface‐site exclusion and blocking mechanisms induced by the presence of colloids are more important than colloid sorption in promoting atrazine mobility in subsurface soil environments.

Comparison of measured and simulated atrazine mobility in two alluvial soils

Atrazine was applied on a sandy loam, Typic Fluvaquent and a silty loam, Typic Udifluvent at a 1.4 kg ha −1 a.i. rate on March 28, 1989. One month later, soil samples were taken at a 60 cm depth for measurement of the atrazine concentration. Similar concentrations were measured in the two soils. The atrazine transport was also simulated by using a physically-based model (HYDRUS). Analyses showed that HYDRUS predicted the atrazine mobility. A sensitivity analysis of the model with respect to sorption, degradation and hydraulic parameters showed that the sorption one was the most relevant in the simulation process. By calibrating the model with the best-fitted Kd value, the model predictions were appreciably improved.

The mobility, partitioning and degradation of atrazine and simazine in the salt marsh environment

The transfer of the s-triazine herbicides onto a salt marsh and their subsequent behaviour and fate has been investigated in a series of laboratory-based experiments. The results indicate that atrazine and simazine enter the marsh system and undergo negligible adsorption onto suspended solids. Herbicide accumulation within the sediment compartment was thought to be due to other mechanisms such as partitioning into the surface microlayer, or association with sediment flocs. s-Triazine mobility within the sediment was dictated by compound and sediment type, reflecting greater mobility in the mud flat than the vegetated marsh sediment. The majority of the herbicides were, however, retained in the uppermost layers of the sediment profile indicating that salt marsh sediments act as a sink for these compounds. Although degradation rates in the sediment were relatively rapid, detectable levels of the parent compounds were still evident after 71 days, which implies that these compounds may persist in salt marsh sediments. The absence of degradation in the aqueous phase implies that adsorption to particulate matter is a prerequisite for the degradation of the s-triazine herbicides.

Mobility and Dissipation of 14C-Labeled Atrazine, Metolachlor, and Primisulfuron in Undisturbed Field Lysimeters of a Coastal Plain Soil

Mobility and dissipation of 14 C-labeled atrazine, metolachlor, and primisulfuron were evaluated for 1 year when applied preemergence to fallow loamy sand soil column field lysimeters. The relative mobility of the herbicides and/or metabolites in field lysimeters over the 1 year period in descending order was metolachlor>atrazine=primisulfuron. Thirty days after treatment, losses of 14 C due to apparent volatilization, with other loss mechanisms being involved, accounted for 57, 43, and 62% of the applied 14 for atrazine, metolachlor, and primisulfuron, respectively. Chemical analysis of the 0-8 cm layer showed the presence of four metabolites for atrazine, two for metolachlor, and two for primisulfuron. Calculated half-lives were 4 days for atrazine, 7 days for metolachlor, and 5 days for primisulfuron

Pesticide Adsorption and Leaching in Soil: An ELISA Laboratory Experiment

Inexpensive pesticide measurement by Enzyme-Linked Immunosorbent Assay (ELISA) technology, widely used for environmental monitoring, may be a useful tool for providing instruction on the environmental fate of pesticides in the classroom. A laboratory experiment that provides instruction in state-of-the-art ELISA pesticide testing methods and demonstrates the effect of soil organic matter content on atrazine (6-chloro-N-ethyl-N′-(1-methylethyl)-1,3,5-triazine-2,4-diamine) transport is described. Atrazine transport through several soils was determined by a column leaching study. Atrazine adsorption by soils was also determined in a distribution coefficient (Kd) study. Results from both studies were used to predict the relative mobility of atrazine in a soil with an unknown organic carbon (OC) content. Results from a classroom experiment showed atrazine from soil column leachate was directly related to soil OC content. Column leachates from Clarion (fine-loamy mixed mesic Typic Hapludoll) (3.1% OC) and Dougherty (loamy, mixed, thermic Arenic Haplustalf) (0.7% OC) soils contained 0.8 and 27.6 μg L–1 atrazine, respectively. Results from the column study were consistent with results from the Kd study. Atrazine in column leachate was inversely related to calculated Kd values of 8.2 and 2.2 L kg–1 for the Clarion and Dougherty soils, respectively. Atrazine in the column leachate of an unknown soil with an intermediate Kd value of 4.1 L kg–1 was 9.2 μg L–1. The ELISA experiment requires minimal supplies and can easily be incorporated into soil science classes or other courses concerned with water quality.