Hydroxyatrazine Research Articles

Evaluation of continuous distribution models for rate‐limited solute adsorption to geologic media

We develop two mathematical models for coupled solute transport and nonlinear adsorption to geologic media. Both models quantify nonuniformity in mass transfer rates with parameters that vary according to a gamma (γ) probability density function. The multisite model, which describes surface‐reaction controls on adsorption kinetics, solves equations for a second‐order rate law. The adsorption rate coefficient of the kinetics equation is correlated with a γ‐distributed desorption rate coefficient. The mobile‐immobile model is based on the assumption that rate limitations are diffusion controlled and account for a γ distribution in solute exchange rates between zones of mobile and immobile water. Solute adsorption in the immobile zone is quantified with the nonlinear expression for the Langmuir equilibrium isotherm. We test the models against results of column experiments on the transport of hydroxyatrazine (HA), a persistent contaminant produced from the degradation of atrazine. We find that the experimental data are matched more closely by calculations of the multisite model than by calculations of the mobile‐immobile model, suggesting that HA adsorption can be understood best as a kinetics reaction with a solid phase composed of binding sites with a broad distribution in adsorption and desorption energies.

DIFFUSION AND DEGRADATION OF ATRAZINE IN A WATER/SEDIMENT SYSTEM

This study determined the effects of temperature and residence time on diffusion and degradation of [14C]atrazine applied to the surface of sterilized and nonsterilized river water over a sediment. Water and sediment were placed in glass columns and incubated at 5 or 24°C. Samples were collected at 0, 7, 14, 28, 42, 56, and 112 d before and after disturbance. The warmer temperature (24°C) initially increased the rate of 14C distribution in the aqueous phase. Disturbance caused approximately 15% of the total 14C to be removed from the aqueous phase by sterile or unsterile sediment incubated at 5°C. At 24°C, the level of 14C in disturbed sediments incubated for more than 28 d gradually increased. This increased retention of 14C by sediment coincided with greater detection of the polar metabolite hydroxyatrazine (HA). More HA was recovered in nonsterilized than in sterilized sediments, indicating the contribution of biological processes to the production of this metabolite. In undisturbed sediments at 24°C, approximately 32% and 10% of the applied 14C permeated the top and bottom 1-cm segments, respectively. In columns incubated at 5°C, less than 5% of the 14C reached the surface of the submerged sediment. The potential impact of atrazine on biota associated with sediment would diminish with time because of dilution in the aqueous phase, transformation to HA, and bound residue formation.

A study on the behaviour of pesticides and their transformation products in the Scheldt estuary using liquid chromatography-electrospray tandem mass spectrometry.

Off-line solid-phase extraction (SPE) combined with liquid chromatography-electrospray tandem mass spectrometry (LC-ESI-MS-MS) was used to study the estuarine behaviour of the polar pesticides, atrazine, chloridazon, diuron and metolachlor, and their transformation products (TPs), hydroxyatrazine (HA), desisopropylatrazine (DIA), desethylatrazine (DEA), 3,4-dichlorophenylmethylurea (DPMU) and monuron. The compounds were identified by comparing their LC retention times and product-ion spectra with those of standard solutions. In all but one case the detection limits of the method were sufficient to determine the compounds of interest over the entire salinity range in the estuary. The concentrations of the dissolved pesticides ranged from 70 ng l-1 for chloridazon to 1350 ng l-1 for diuron. The levels of TPs were 3-8% of the levels of their parent pesticide. The mixing plots of polar pesticides and their TPs indicated that TPs, which are present in fresh river water, are conservatively transported to the sea and that no additional amounts of TPs are formed during their transport through the estuary. The one exception was HA, of which approximately 10% of the amount transported to the North Sea is formed in the lower part of the estuary by photochemical oxidation of atrazine. The latter was concluded from the ratios of each analyte over the sum total of the parent pesticide and all TPs along the salinity gradient, which proved to be a useful tool for identifying such estuarine transformations.

Hydroxyatrazine in soils and sediments.

Hydroxyatrazine (HA) is the major metabolite of atrazine in most surface soils. Knowledge of HA sorption to soils, and its pattern of stream water contamination suggest that it is persistent in the environment. Soils with different atrazine use histories were collected from four sites, and sediments were collected from an agricultural watershed. Samples were exhaustively extracted with a mixed-mode extractant, and HA was quantitated using high performance liquid chromatography with UV detection. Atrazine, deethylatrazine (DEA), and deisopropylatrazine (DIA) were also measured in all samples. Concentrations of HA were considerably greater than concentrations of atrazine, DEA, and DIA in all soils and sediments studied. Soil concentrations of HA ranged from 14 to 640 μg/kg with a median concentration of 84 μg/kg. Sediment concentrations of HA ranged from 11 to 96 μg/kg, with a median concentration of 14 μg/kg. Correlations of HA and atrazine concentrations to soil properties indicated that HA levels in soils were controlled by sorption of atrazine. Because atrazine hydrolysis is known to be enhanced by sorption and pH extremes, soils with high organic matter (OM) and clay content and low pH will result in greater atrazine sorption and subsequent hydrolysis. Significant correlation of HA concentrations to OM, pH, and cation exchange capacity of sediments indicated that mixed-mode sorption (i.e., binding by cation exchange and hydrophobic interactions) was the mechanism controlling HA levels in sediment. The presence of HA in soils and stream sediments at the levels observed support existing hypotheses regarding its transport in surface runoff. These results also indicated that persistence of HA in terrestrial and aquatic ecosystems is an additional risk factor associated with atrazine usage.

Analysis of atrazine, terbutylazine and their N-dealkylated chloro and hydroxy metabolites by solid-phase extraction and gas chromatography–mass spectrometry and capillary electrophoresis–ultraviolet detection

Solid-phase extraction (SPE) with the styrene–divinylbenzene adsorbent LiChrolut EN was investigated for the extraction of the s-triazine herbicides atrazine and terbutylazine, their polar N-dealkylated degradation products deethylatrazine (DEA), deisopropylatrazine (DIA) and deethylterbutylazine (DET) and for the hydrophilic hydroxytriazine degradation products (HTDPs) hydroxyatrazine (HA), hydroxyterbutylazine (HT), deethylhydroxyatrazine (DEHA), deisopropylhydroxyatrazine (DIHA) and deethyldeisopropylhydroxyatrazine (ameline). The optimum pH value for the extraction of the HTDPs from fortified tap water at 2 μg/l is 3.0. Recovery values with 200 mg LiChrolut EN are >80% for HA, HT, DEHA and 30% for DIHA from 200 ml spiked tap and river water. Atrazine, terbutylazine, DEA, DIA and DET are quantitatively extracted by LiChrolut EN. The chlorotriazines are analyzed by GC–MS and the HTDPs by capillary zone electrophoresis (CZE) and micellar electrokinetic capillary chromatography (MECC) with an acetate buffer at pH 4.6 or a sodium borate–sodium dodecyl sulfate buffer at pH 9.3. The combined method of SPE enrichment and CE analysis allows the determination of HTDPs in the low μg/l range.

Extractability and degradation of atrazine in a submerged sediment

A study was conducted to examine the effects of residence time and temperature on atrazine extractability and degradation in a sediment generated from Emporia sandy loam soil submerged under a water column. Sediments amended with 2.8 μg of atrazine were incubated at two temperatures (5 and 24 C), sampled at 0, 14, 28, 112, 168, 252, and 336 d, and then sequentially extracted once with 80 ml 0.01 M CaCl2 aqueous solution, three times with 25 ml of methanol/water mixture (4:1, v/v), and three times with 25 ml of methanol/water/formic acid (20:5:1, v/v pH 3.2) for a total of seven times. Extracts were analyzed for atrazine and metabolites using reverse phase high-performance liquid chromatography. The rate of bound residue formation was greater at 24 than at 5 C. About 30 and 60% of the 14C was bound (nonextractable) to sediments at 5 and 24 C, respectively. Water was less effective in extracting 14C residues from sediments incubated at 24 C than at 5 C. Acidification of the methanol/water mixture with formic acid during the last extraction step improved the removal of hydroxyatrazine from sediment. Atrazine degraded primarily to hydroxyatrazine (HA) and to a lesser extent to deethylatrazine (DEA). Although no DEA was found, HA at 43 μg kg−1 of sediment was detected 112 d after treatment at 5 C, indicating that chemical degradation could occur at a low temperature if sediments are incubated for extended periods of time. At 24 C, HA was found within 28 d and reached the maximum level at day 252. The results suggested that HA is the major metabolite of atrazine in the sediment; a significant fraction of the residue was unavailable for extraction, and this unextractable portion increased with residence time.

Contribution of Hydroxylated Atrazine Degradation Products to the Total Atrazine Load in Midwestern Streams

The contribution of hydroxylated atrazine degradation products (HADPs) to the total atrazine load (i.e., atrazine plus stable metabolites) in streams needs to be determined in order to fully assess the impact of atrazine contamination on stream ecosystems and human health. The objectives of this study were (1) to determine the contribution of HADPs to the total atrazine load in streams of nine midwestern states and (2) to discuss the mechanisms controlling the concentrations of HADPs in streams. Stream samples were collected from 95 streams in northern Missouri at preplant and postplant of 1994 and 1995, and an additional 46 streams were sampled in eight midwestern states at postplant of 1995. Samples were analyzed for atrazine, deethylatrazine (DEA), deisopropylatrazine (DIA), and three HADPs. Overall, HADP prevalence (i.e., frequency of detection) ranged from 87 to 100% for hydroxyatrazine (HA), 0 to 58% for deethylhydroxyatrazine (DEHA), and 0% for deisopropylhydroxyatrazine (DIHA) with method detectio...

Sorption and Desorption of Atrazine, Deethylatrazine, and Hydroxyatrazine by Soil and Aquifer Solids

AbstractAdsorption kinetics and adsorption/desorption isotherms of atrazine (AT), and its degradation products, deethylatrazine (DEA) and hydroxyatrazine (HyA) on solids from two depths of a gleyic planosol and the underlying sandy aquifer were studied using laboratory batch systems. Adsorption of the three molecules decreased with the sampling depth of the solid. Atrazine and DEA were not adsorbed on the aquifer solids, whereas HyA was. For all three solids, the adsorption increased in the order DEA < AT << HyA. Adsorption equilibrium was reached after 72 h for the upper soil sample (0‐0.33 m) and after 24 h for the deeper soil sample (0.9–1.05 m) for all three molecules. For HyA, equilibrium was reached after 24 h for the aquifer solid (6–7 m). High pressure liquid chromatography (HPLC) analyses showed no significant degradation of the three molecules after 72 h. The adsorption isotherms of the three molecules were described by Freundlich equations. The Kfads values ranged from 3.1 to 0.4 L kg−1 for AT, 1.5 to 0.3 L kg−1 for DEA and 7.9 to 0.9 L kg−1 for HyA. The Koc values suggested that the affinity for the organic matter bound to the solid increased in the order DEA < AT << HyA. The desorption isotherms were also described by Freundlich equations. The Kfdes value was 7.5 L kg−1 for AT in the upper soil sample and ranged from 0.1 to 31.1 L kg−1 for DEA and from 0.7 to 96.8 L kg−1 for HyA, depending on the sample. In the upper soil sample, desorption was hysteretic and DEA and HyA formed nonextractable residues, HyA more so than DEA. For the deeper soil sample for all three compounds and the aquifer solids for HyA, adsorption was completely reversible and did not lead to the formation of nonextractable residues.

Microbore liquid chromatographic-mass spectrometric determination of atrazine and its major hydroxylated degradate in water at parts-per-trillion levels using electrospray

A liquid chromatography-electrospray ionization mass spectrometry (LC-ESI-MS) method was developed to determine atrazine (ATR) and hydroxyatrazine (HA) in water at parts-per-trillion (ppt) levels. In addition to protonaed molecular ions, sodiated molecular and dimer ions were observed in full-scan electrospray mass spectra of the analytes, providing additional information for the identification of ATR and HA. The quantification is based on the use of isotopically labeled internal standards that were added to water samples prior to the sample extraction using a carbon black cartridge. The relative response factor for each of the native compounds relative to its corresponding internal standard was measured and used to minimize the analytical error. The precision and accuracy data were obtained from the analysis of standard water samples containing 50 ppt ATR and 100 ppt HA. Relative standard deviation and relative error are less than 15% ( n=6) for both ATR and HA determinations. The method has been successfully used to analyze agricultural run-off samples for ATR and HA levels. Analytical results compared well with those obtained by using GC-high-resolution and fast atom bombardment high-resolution MS methods developed in this laboratory. Preliminary results for analysis of a standard containing a mixture of ATR, HA, deethylatrazine and deisopropylatrazine suggest that the LC-ESI-MS method can be applied to simultaneous trace-level determination of the major products of atrazine degradation in the environment.

Adsorption and Desorption of Atrazine, Deethylatrazine, Deisopropylatrazine, Hydroxyatrazine, and Metolachlor in Two Soils from Virginia

The objective of this study is to characterize the adsorption-desorption properties of atrazine, deethylatrazine (DEA), deisopropylatrazine (DIA), hydroxyatrazine (HA), and metolachlor in the Emporia (fine loamy, siliceous, thermic Typic Hapludult) and Cullen (clayey, mixed, thermic Typic Hapludult) soils. Adsorption and desorption isotherms were determined using the batch equilibrium procedure. Four solution concentrations (2.5, 7.5, 13.2, and 26.4 µmol L−1) were prepared of each chemical and four 24-h desorption periods at each concentration followed immediately after the adsorption process. Organic carbon distribution coefficients (Koc ranged from 140 to 234 for atrazine, 80 to 110 for DEA, 128 to 130 for DIA, 493 to 609 for HA, and 162 to 190 for metolachlor. For desorption, all chemicals exhibited hysteresis. Hysteresis was quantified: ω = [1/nads ÷ 1/ndes − 1] × 100. Soil type affected the degree of atrazine, DEA, and metolachlor hysteresis (ω), and initial concentration had a significant effect on ω only in the Cullen soil. The amount of chemical desorbed, expressed as the percentage of the amount adsorbed, was about 60% for DEA, 43% for atrazine, 40% for metolachlor, 37% for DIA, and 31 and 17% for HA on the Emporia and Cullen soils, respectively. Soil type and initial concentration had no significant effect on the percentage of chemical desorbed except for HA. The sorption properties for atrazine and metolachlor in these soils are similar. The tendency of HA to leach will be low in these soils compared with atrazine, while the tendency of DEA to leach will be high.

Adsorption and Desorption of Atrazine, Deethylatrazine, Deisopropylatrazine, and Hydroxyatrazine on Levy Wetland Soil

The adsorption and desorption of atrazine, and its three metabolites, deethylatrazine (DEA), deisopropylatrazine (DIA), and hydroxyatrazine (HA), on Levy wetland soil were measured using the batch equilibration technique. Solution concentrations for each chemical were 1.3, 3.8, 6.6, and 13.2 μmol L-1. Four 24-h period desorptions for each concentration were conducted immediately after adsorption. The adsorption of all the chemicals conformed to linear isotherms. Adsorption coefficients decreased in the order HA (109.7) > atrazine (38.6) > DIA (26.3) > DEA (22.1). The organic carbon partition coefficients (Koc) for HA, atrazine, DIA, and DEA were 1500, 440, 290, and 240 L kg-1, respectively. Percent of chemical desorbed was about 29% for DEA, 24% for atrazine, 23% for DIA, and 16% for HA. The slopes of all desorption isotherms were less than their respective adsorption slopes, indicating hysteresis. Atrazine and its metabolites were relatively more strongly adsorbed and the binding was less reversible in t...

Hydroxylated Atrazine Degradation Products in a Small Missouri Stream

This research assessed the occurrence of hydroxylated atrazine degradation products (HADPs) in streamwater from Goodwater Creek watershed in the claypan soil region of northeastern Missouri. Streamwater was sampled weekly from June 1992 to December 1994 at a V-notch weir used to measure streamflow for this 7250-ha watershed. Filtered water samples were prepared by cation exchange solid-phase extraction and analyzed for hydroxyatrazine (HA), deethylhydroxyatrazine (DEHA), and deisopropylhydroxyatrazine (DIHA) by high-performance liquid chromatography with UV detection. HADPs were confirmed by mass spectrometry and an alternative HPLC/UV method. Frequency of HADP detection was 100% for HA, 25% for DEHA, and 6% for DIHA. Concentrations ranged from 0.18 to 5.7 μg L -1 for HA, from <0.12 to 1.9 μg L -1 for DEHA, and from <0.12 to 0.72 μg L -1 for DIHA. These results establish that HADPs can contaminate surface water and that HA contamination of surface water is a significant fate pathway for atrazine in this watershed.

Fate of 14C-Atrazine in a Silt Loam Soil

Abstract Formation of 14C-atruzine degradation products and their distribution in the top 90 cm of a silt loam soil was determined during 16 months in the field. After 16 months. 68% of the applied 14C was still present in the soil. By 12 months after treatment (MAT). 14C leached to 70–80 cm. Atrazine accounted for 24% of the applied 14C remaining 16 MAT, and was the predominant 14C-compound below 10 cm through 16 MAT. Hydroxyatrazine (HA) was the major degradation product in the top 10 cm of soil comprising 13% of 14C present I MAT and increasing to 24% by 12 MAT. Predominant degradation products at depths greater than 10 cm were HA and deethylatrazine (DEA). Deisopropylatrazine (DIA) accounted for less than 6% of the radioactivity recovered at any soil depth. Deethyldeisopropylatrazine (DEDIA) was detected in soil extracts 2 MAT indicating further degradation of DIA and DEA. The proportion of DEA and DIA increased while the proportion of HA decreased at increasing soil depths indicating that DEA and DIA...

Formation and Movement of14C-Atrazine Degradation Products in a Clay Loam Soil in the Field

Formation of14C-atrazine degradation products and their distribution in the top 90 cm of soil was determined over 16 mo in a Webster clay loam in the field. After 16 mo, 64% of the applied14C could still be accounted for in the 90-cm soil profile. At 1 mo after treatment (MAT),14C moved to the 70- to 80-cm depth. Rapid movement of radioactivity could be attributed in part to preferential movement through vertical macropores. Atrazine accounted for 32% of the14C applied 16 MAT and was the predominant14C-compound in soil below 10 cm through 12 MAT. Hydroxyatrazine (HA) was the major degradation product in the top 10 cm of soil accounting for 9% of the14C present 1 MAT and increasing to 24% within 6 MAT. Deethylatrazine (BEA) was the predominant degradation product at depths greater than 10 cm, accounting for 26% of the14C in the 10- to 20-cm depth 16 MAT. Deisopropylatrazine (DIA) accounted for less than 10% of the14C recovered at any soil depth. Deethyldeisopropylatrazine (DEDIA) and an unidentified product were detected in soil extracts 1 MAT indicating further degradation past primary metabolites. The proportion of DEA and DIA increased while the proportion of HA decreased as soil depth increased indicating that DEA and DIA are more mobile in soil than HA. The large amount of radioactivity remaining in the soil 16 MAT suggests that a large pool of atrazine and its degradation products are present in the soil for a long period of time, having the potential to move deeper in the soil and ultimately contaminate ground water.

Liquid-Solid Extraction and Fast Atom Bombardment High-Resolution Mass Spectrometry for the Determination of Hydroxyatrazine in Water at Low-ppt Levels

Parts-per-trillion levels of hydroxyatrazine (HA) have been quantitatively extracted and eluted from water by liquid-solid extraction with a graphitized carbon-black cartridge. Recoveries of HA (>80%) for this procedure are superior to those obtained when a C-18 cartridge or liquid-liquid extraction with dichloromethane are used. Quantification of HA at picogram levels was accomplished by using isotope dilution and fast atom bombardment high resolution mass spectrometry. No significant interfering spectral background occurs at the masses of interest, those of the [M+H] + ions of both the analyte and the internal standard, when the liquid matrix is 3:1 dithithreitol/dithioerythritol

Adsorption and extraction of hydroxyatrazine from wetland sediment

Abstract We investigated the adsorption characteristics of hydroxyatrazine (HA) and introduced a relatively simple method to analyze and extract the compound from wetland sediment. Although concentration of HA could be easily measured using an amino‐phase HPLC column, one should be cautious not to use solvent programs that interfere with atrazine (A). The adsorption characteristic of HA on wetland sediment was roughly linear with a distribution coefficient of 0.057 L/g. About 90% of HA adsorbed on the sediment was recovered using our heated extraction method.

Influence of carbon and nitrogen application on the mineralization of atrazine and its metabolites in soil

AbstractIt has been proposed that levels of carbon and nitrogen in soil affect the rate at which triazine herbicides degrade. The present study was designed to investigate the effects of varying the levels of initial soil carbon and nitrogen as well as the effects of a later carbon addition on the mineralization of atrazine and its metabolites in soil. Atrazine degradation in soils amended with carbon as mannitol, and with nitrogen as urea, at levels of 10, 30, 50, or 80 mg kg−1 mannitol, urea, or mannitol and urea was similar to degradation in unamended soils. Only 39% of applied atrazine was mineralized after 326 days regardless of the initial carbon or nitrogen treatment. In contrast, a second mannitol amendment of 1 g kg−1 soil at day 140 increased [14C]carbon dioxide evolution by an additional 17% as a result of enhancing the mineralization rate of the atrazine metabolites. This conclusion is supported by our finding that periodic extraction of the soil with methanol followed by quantification on HPLC showed complete dissipation of the parent atrazine in 120 days. The metabolites hydroxyatrazine (HA), deisopropylatrazine (DIA), deethylatrazine (DEA), and diaminochlorotriazine (DACT) began to appear in the methanol extract 10 days following atrazine application. The greatest concentrations of HA, DEA, DIA. and DACT in the methanol extracts were 19, 12.4, 10.1, and 6.7% of applied atrazine, respectively. These concentrations were observed at day 95 except for DEA where the concentration continued to increase until day 142. A second soil extraction with hydrochloric acid (1m) + methanol (20 + 80 by volume) recovered additional HA, deethylhydroxyatrazine (DEHA), deisopropylhydroxyatrazine (DIHA), and DACT. When the extraction data were combined, 31.9, 12.4, 10.1. 10.2, 12.0 and 7.8% of applied atrazine was recovered as HA, DEA, DIA, DEHA. DIHA, and DACT, respectively. Combustion of the extracted soil showed 20% of the applied atrazine remained as soil‐bound residues after 326 days.

Analysis of Hydroxylated Atrazine Degradation Products in Water Using Solid-Phase Extraction and High-Performance Liquid Chromatography

The fate of hydrowylated atrazine degradation products (HADPs) has not been studied extensively in aquatic environments because there are no published quantitative analytical methods that do not use radioisotopes. This paper presents a new method that has been developed to analyze these degradation products in water. Three HADPs, hydroxyatrazine (HA), deethylhydroryatrazine (DEHA), and deisopropylhydroryatrazine (DIHA), were extracted, concentrated, and purified from spiked (1 or 5 ppb) laboratory water and stream water samples (0.25 L) using SCX (propylbenzenesulfonic acid) cation-erchange, solid-phase extraction columns

Formation and Movement of14C-Atrazine Degradation Products in a Sandy Loam Soil Under Field Conditions

Formation and distribution of14C-atrazine degradation products in the top 120 cm of soil were determined over 16 mo under field conditions in an Estherville sandy loam. After 16 mo, 78% of applied14C was still present in the soil. By 2 mo after treatment (MAT),14C had moved to the 30- to 40-cm depth; however, movement to depths greater than 40 cm was not observed. Greater than 98% of the14C remaining in the soil profile after 16 mo was in the top 20 cm. Twenty-seven percent of the14C applied was atrazine 16 MAT. Atrazine was the predominant14C-compound in soil below 10 cm. Hydroxyatrazine (HA) was the major degradation product in the top 10 cm of soil. The proportion of14C as HA in the top 10 cm increased from 15% 2 MAT to 37% 16 MAT. Deethylatrazine (DEA) was the predominant degradation product at the 10- to 30-cm depth and accounted for up to 23% of the14C present in the 10- to 20-cm depth. Deisopropylatrazine (DIA) accounted for less than 6% of the radioactivity recovered at any soil depth. The proportion of DEA and DIA increased while the proportion of HA decreased as soil depth increased, indicating that DEA and DIA are more mobile in soil than HA. Detection of HA at depths greater than 10 cm appears to be due to in situ degradation of atrazine previously moved to that soil depth. The large amount of14C remaining in the soil 16 MAT suggests that a large pool of atrazine and its degradation products are present in the soil for an extended period following application and have the potential to contaminate ground water.

Degradation and bound residue formation of four atrazine metabolites, deethylatrazine, deisopropylatrazine, dealkylatrazine and hydroxyatrazine, in a Western Tennessee soil

AbstractAtrazine (2‐chloro‐4‐[ethylamino]‐6‐[isopropylamino]‐1,3,5‐triazine) can be degraded to several metabolites in soil that include the dealkylated metabolites, deethylatrazine (DEA), deisopropylatrazine (DIA) and dealkylatrazine (DAA), and the dechlorinated metabolite, hydroxyatrazine (HYA). Biological and physical degradation and soil‐bound residue formation from uniformly 14C ring‐labeled DEA, DIA, DAA and HYA were characterized in a western Tennessee soil using intact surface soil core microcosms.Metabolites were applied to soil microcosms at a rate of 0.5 kg/ha (˜1.2 μg/g soil). Concentrations of the dealkylated metabolites in nonirradiated soil microcosms decreased to less than 2% of the applied compound or were not detected after 180 d incubation. Hydroxyatrazine residues decreased to 33% of the applied concentration. In nonirradiated microcosms after 180 d, evolution of 14CO2 from radiolabeled DEA, DIA, DAA and HYA increased to 25, 16, 59 and 21%, respectively, of the total radiolabel added. Irradiated soil microcosms evolved 0.6, 1.7, 0.1 and 0.9%, respectively, of the total radiolabel added. Rates of dissipation for the four metabolites followed first‐order kinetics. Half‐lives for the dealkylated metabolites, based on extractable residues, ranged from 17 to 26 d, whereas HYA was 121 d. Soil‐bound 14C residues increased in concentration in nonirradiated microcosms and ranged from 28% of the applied radiolabel for HYA to 60% for DEA after 180 d. In irradiated microcosms the range was from 24% for HYA to 72% for DAA on day 180. Extractable 14C residues in all microcosms decreased in concentration during this study and, after 180 d, ranged from 4% of the radioactivity added for DAA to 40% for HYA. Extractable 14C residues in irradiated microcosms ranged from 31% of the initial activity for DAA to 68% for HYA at the termination of the study.