Deethylatrazine Research Articles

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...

Atrazine mineralisation in New Zealand topsoils and subsoils: influence of edaphic factors and numbers of atrazine-degrading microbes

The mineralisation of 14C-ring-labelled atrazine to 14CO2 was measured in 3 contrasting New Zealand soils under controlled conditions of temperature and moisture. The numbers of atrazine-degrading organisms were measured by a most probable number technique. Decomposition rates were slow, with a maximum of 41% of atrazine being mineralised over 263 days. Mineralisation was generally very low in subsoils and was much reduced by low moisture content. However, one subsoil from 60–90 cm depth had unusually high numbers of atrazine-degrading microbes and showed mineralisation greater than or equivalent to the surface soil. Mineralisation was approximately doubled by a 10°C rise in temperature over the range 16–28°C. In general, the rate of atrazine mineralisation over 7–96 days could be predicted from the number of atrazine-degrading microbes and the cation exchange capacity of the soil (R2 = 0·86). A large amount (54–77%) of 14C remained in the soil as non-extractable residues after 263 days, but only trace amounts of the added atrazine or the decomposition products de-ethyl atrazine and de-isopropyl atrazine were detected by extraction in organic solvent.

Optimizing recoveries of two chlorotriazine herbicide metabolites and 11 pesticides from aqueous samples using solid-phase extraction and gas chromatography–mass spectrometry

A method was developed for solid-phase extraction of two chlorotriazine herbicide metabolites, deethylatrazine (DEA) and deisopropylatrazine (DIA), from aqueous samples. Two C 18 phases in cartridge format were compared and recoveries were found to be highly sensitive to sorbent amount, sample volume and presence of parent compounds. Recoveries were significantly improved using a partially non-endcapped C 18 phase compared to the normal C 18 phase, particularly for DIA, apparently due to polar interactions. Combinations of sample volume and sorbent amount were tested using deionized water to determine an optimal combination of 200 ml and 1.0 g, respectively. Recoveries from a variety of river, stream, runoff and ground waters averaged 105–116% and 109–117% at concentrations of 0.5–1.0 ng/ml for DIA and DEA, respectively, with minimum detection limits of 0.05 ng/ml. Other pesticides tested also have acceptable recoveries using this method.

Enhanced degradation of deethylatrazine in an atrazine‐history soil of Iowa1

The degradation of deethylatrazine (DEA), a major metabolite of atrazine, was studied by using radiotracers in soils with two different atrazine histories. DEA degradation was enhanced in soils which had received long‐term exposure to atrazine (atrazine‐history soil) compared with soils that had not received long‐term atrazine exposure (no‐history soil). After 60 days of incubation, mineralization of DEA to 14CO2 in the atrazine‐history surface soil was twice that in the no‐history surface soils, with 34% and 17% of the applied 14C‐DEA as CO2, respectively. In surface soils, 25% of the applied 14C remained as DEA in the atrazine‐history soil, compared with 35% in the no‐history soil. Microbial plate counts indicated an increase in numbers of bacteria and fungi in soils incubated with DEA compared to control soils. No significant difference in total microbial respiration was seen among atrazine‐history and no‐history soils incubated with DEA, but DEA‐treated soils had greater microbial respiration than untreated control soils after 6 days. A 14C‐most‐probable‐number procedure was used to enumerate specific DEA degraders. A greater number of DEA degraders were indicated in atrazine‐history subsurface soil compared with all other soils in this study (p < 0.05). From this study, it appears that an increase in microbial activity contributes to decreased persistence and increased degradation of DEA in soils that have had long‐term exposure to atrazine at field application rates, compared to soils with no long‐term exposure. Decreased persistence of this major metabolite of atrazine in atrazine‐history soils is important in that there will be less available for movement in surface runoffs.

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 &lt; AT &lt;&lt; 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 &lt; AT &lt;&lt; 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.

Comparative Fates of Atrazine and Deethylatrazine in Sterile and Nonsterile Soils

AbstractAssessment of biotic and abiotic mechanisms of atrazine (ATR) and deethylatrazine (DEA) breakdown is necessary to identify major degradation pathways and understand soil conditions necessary for these mechanisms to occur. Our purpose was to compare fates of ATR and DEA in laboratory radiotracer studies to elucidate the effects of soil moisture status and soil depth on degradation and persistence. Atrazine and DEA were more persistent in subsurface soil than in surface soil. After 120‐d incubation, bound residues were significantly greater in surface soils than in subsurface soils. In 14C‐DEA‐treated soil, biological activity contributed to decreased persistence of DEA in saturated surface soil in contrast with unsaturated surface soil after 60 d. Biological activity also contributed to decreased persistence of ATR in saturated subsurface soil in contrast with unsaturated subsurface soil after 120 d, and the decreased persistence corresponded to significantly greater amounts of DEA, deisopropylatrazine (DIA), and polar degradation products compared with other treatments. The percentage of applied 14C‐ATR that degraded to DEA and DIA increased approximately threefold during the 60‐ to 120‐d incubation in nonsterile saturated subsurface soil. Greater quantities of polar degradation products were formed in 14C‐DEA‐treated nonsterile compared with sterile soils. Half‐lives (from first‐order degradation rate constants) of ATR and DEA were significantly longer in subsurface soil compared with surface soils. Biotic mechanisms contributed to the half‐lives of ATR (in surface and subsurface soil) and DEA (in subsurface soil) being significantly shorter under saturated soil moisture conditions compared with unsaturated soil moisture conditions.

Herbicide Persistence and Mobility in Recharge Lake Watershed in York, Nebraska

AbstractElevated levels of herbicides in surface and groundwater are a concern in the Cornbelt in the USA. This study was conducted to interpret the herbicide behavior in a watershed system using data collected from runoff, Recharge Lake, and groundwater influenced by agriculture and lake seepage. The York Ground Water Recharge Project was constructed on a tributary of Beaver Creek, which drains a 3327‐ha watershed of primarily row‐cropped heavily irrigated farmland. The estimated average runoff is 1.48 × 106 m3 yr−1 under a precipitation norm of 635 mm yr−1. Maximum atrazine (2‐chloro‐4‐ethylamino‐6‐isopropylamino‐s‐triazine) inputs to Recharge Lake occurred in May and June runoff events and resulted in average lake concentrations of 36 and 17 µg L−1 in 1993 and 1994, respectively. Only about 0.28 and 0.19% of total applied atrazine was lost to runoff in 1993 and 1994, respectively. The deethylatrazine (DEA) to atrazine molar ratio (DAR) decreased rapidly over a period of several hours in runoff samples, which is consistent with inputs from recently atrazine‐treated soil. After the spring runoff, herbicide levels in Recharge Lake rose rapidly in response to the runoff event, then diminished gradually over a period of months. Atrazine concentrations in Recharge Lake decreased exponentially with time. Degradation half‐lives were 237 d (r = 0.93) in 1993 and 209 d (r = 0.91) in 1994. Adjusted DEA concentrations in Recharge Lake remained relatively constant, indicating little evidence for biotic degradation and suggesting that abiotic degradation of atrazine to hydroxyatrazine (2‐hydroxy‐4‐ethylamino‐6‐isopropylamino‐s‐triazine) was the most likely major degradative pathway in Recharge Lake.

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.

On-line and off-line solid-liquid extraction and liquid chromatographic analysis at trace levels, for monitoring of herbicides and their degradation products in river and fluvioestuarine freshwater-seawater interfaces

Monitoring of trace levels of phenylurea and chlorotriazine herbicides and their metabolites deispropylatrazine (DIA) and deethylatrazine (DEA) was performed on river, estuarine and coastal seawater by off-line ( n-octadecyl silica, C 18) and on-line (styrene-divinylbenzene copolymer-based, PRP1) preconcentration techniques using reversed-phase chromatography and UV and electrochemical detection. It is shown that off-line and on-line technology fit monitoring of trace-level phenylurea and triazine analysis (detection limit 10–50 ng/l) in freshwater as well as seawater and in natural water with high dissolved organic carbon (DOC) content. Clean-up was unnecessary for most of the surface water sample for both off-line and on-line techniques. Samples of surface water originating from various rivers (Seine, Charente, Garonne), canals (Marennes-Oléron) and estuaries (Charente, Seudre salinity gradient up to 30‰) were analysed. Dissolved organic carbon (DOC) contents varied from <1 to 15 mg/1 and provided numerous interferents and a major ‘hump’ whose intensity is correlated with DOC content, suggesting that a major part of the organic matter, namely humic substances, is retained on the solid phase and eluted as polar compounds.

Effect of Various Materials in Multilevel Samplers on Monitoring Commonly Occurring Agrichemicals in Ground Water

AbstractStudies have shown that materials, such us polytetra‐fluoroethylene (PTFE), rigid polyvinyl chloride (rigid PVC). flexible polyvinyl chloride (flexible PVC), stainless steel (SS). low‐density polyethylene (LDPE), and high‐density polyethylene (HDPE), have the potential to influence certain analyte concentrations in ground water samples. The effects of HDPE, LDPE, PTFE, rigid PVC, and SS on aqueous concentrations of nitrate‐N, atrazine, deethylatrazine (DEA), and deisopropylatrazine (DIA) were evaluated in a field study A laboratory study was conducted to evaluate sorption of atrazine DEA, DIA, cyanazine, alachlor, metolachlor, and butachlor to PTFE, HDPE, and SS materials. Butachlor is rarely use in the United States, but was included because of its expected high sorptivity. No significant differences between HDPE, LDPE, PTFE, rigid PVC, and SS were determined for any of the analytes tested in the field study. In the laboratory study, sorption of DIA to PTFE and SS was significant at 2.6 × 10−5 and 4.1 × 10−5μg/m2 respectively. Sorption of DIAA to HDPE was not significantly &gt; 0 sorption of all other compounds to HDPE, PTFE, and SS were also not significantly &gt;0. Results of the two studies indicate that for these analytes (relatively polar or ionized compounds), representative ground water samples are not dependent on the materials used for multilevel sampler construction. When considering these compounds, it appears that the least expensive materials (HDPE, rigid PVC, and LDPE) are good choices for the construction of ground water monitoring wells.

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...

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...

A Natural Gradient Transport Study of Selected Herbicides

AbstractThe behavior of trace quantities of commonly detected herbicides and herbicide degradates was investigated in a shallow sand and gravel aquifer. In 1991, a solute pulse containing approximately 15 mg L−1 bromide, 3 μg L−1 atrazine (2‐chloro‐4‐ethylamino‐6‐isopropylamino‐1,3,5‐triazine), 2 μg L−1 alachlor (2‐chloro‐2′,6′‐diethyl‐N‐(methoxymethyl)‐acetanilide), 10 μg L−1 cyanazine (2‐[[4‐chloro‐6‐(ethylamino)‐S‐triazin‐2‐yl]amino]‐2‐methylpropionitrile), and 10 μg L−1 metolachlor (2‐chloro‐N‐(2‐ethyl‐6‐methylphenyl)‐N‐(2‐methoxy‐1‐methylethyl) acetamide) was injected into a shallow aquifer near Fremont, NE. The plume was monitored for 2 mo following injection using an array of multilevel samplers. A second injection in 1992 included approximately 10 mg L−1 bromide, 1 μg L−1 butachlor (2‐chloro‐2′,6′‐diethyl‐N‐(butoxy methyl) acetanilide), and 3 μg L−1 atrazine, deethylatrazine (DEA) (2‐amino‐4‐chloro‐6‐isopropylamino‐1,3,5 triazine) and deisopropylatrazine (DIA) (2‐amino‐4‐chloro‐6‐ethylamino‐1,3,5 triazine). This plume was monitored for 3 mo. Retardation factors (Rs) were determined for each herbicide by comparing concentration profiles to those of the conservative tracer; Rs were calculated as the ratio of first central moments. Results indicated only slight retention of all injected compounds. Retardation factors for atrazine, DEA, DIA, cyanazine, alachlor, and metolachlor were less than 1.3, with butachlor being slightly more retained (R = 1.65). Persistence of the injected compounds was estimated by the decrease with time in area under the breakthrough curves. Atrazine, DEA, DIA, cyanazine, and metolachlor showed no detectable loss. Losses of alachlor and butachlor were approximately 40 and 70%, respectively, in a 2‐mo period.

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.

Determination of atrazine, deethylatrazine and deisopropylatrazine in water and sediment by isotope dilution gas chromatography—mass spectrometry

Methods for the trace analyses of atrazine, deethylatrazine (DEA), and deisopropylatrazine (DIA) in water and sediment have been developed by using stable-isotope dilution with gas chromatography-mass spectrometry detection. Water samples are spiked with known amounts of 13C 3-atrazine, 13C 3-DEA and 13C 3-DIA and submitted to solid-phase extraction with C 18 bonded silica. Pesticides are eluted from the solid phase with ethyl acetate. Sediment samples are spiked and equilibrated with a known amount of each labeled standard before supercritical fluid extraction (SFE) using a 4% (v/v) methanol-CO 2 mobile phase at 43°C and 10 MPa with off-line collection in methanol. A gas chromatograph coupled with a quadrupole mass spectrometer operated in the selected ion monitoring (SIM) mode was used to analyze the concentrated sample extracts. When compared to conventional liquid—liquid extraction methods, these methods decrease extraction time, labor, and solvent volume required. Quantification of the triazines by using isotope dilution compensates for differences in physical recovery for atrazine and its metabolites, especially when large ( > 100 ml) water volumes are extracted. Method detection limits for atrazine, DEA and DIA are 0.02, 0.02 and 0.10 μ g 1 −1, respectively, in water. In sediment, the method detection limits are 0.10, 0.20 and 0.50 ng g −1 for atrazine, DEA and DIA, respectively. More than 4000 water and 800 sediment samples have been analyzed by these methods for more than two years. The average accuracy (bias) for atrazine-fortified water samples is +6.4% ( n = 200) and the precision from duplicate analyses is ±6.0%. Precision of the SFE method for atrazine is ±11% at the 2 ng g −1 level whereas accuracy is −3.2% ( n = 8) for recovery of 13C 3-atrazine standard at the 5 ng g −1 level.

Occurrence of Atrazine and Degradates as Contaminants of Subsurface Drainage and Shallow Groundwater

AbstractAtrazine is a commonly used herbicide in corn (Zea mays L.) growing areas of the USA. Because of its heavy usage, moderate persistence, and mobility in soil, monitoring of atrazine movement under field conditions is essential to assess its potential to contaminate groundwater. Concentrations of atrazine, deisopropylatrazine (DIA), and deethylatrazine (DEA) were measured in subsurface drainage and shallow groundwater beneath continuous, no‐till corn. Water samples were collected from the subsurface drain (tile) outlets and suction lysimeters in the growing seasons of 1990 and 1991, and analyzed for atrazine and two principle degradates using solid‐phase extraction and HPLC. In 1990, atrazine concentration ranged from 1.3 to 5.1 µg L−1 in tile‐drain water and from 0.5 to 20.5 µg L−1 in lysimeter water. In general, concentrations of parent and degradates in solution were atrazine &gt; DEA &gt; DIA. Lesser levels of atrazine were measured in 1991 from Plots 2 and 4; however, greater concentrations of atrazine (6.0–8.4 µg L−1) were measured from Plot 5. Throughout the two growing seasons, atrazine concentration in Plot 5 tile‐drain water was greater than that of Plots 2 and 4, suggesting a preferential movement of atrazine. Concentrations of DIA and DEA ranged from 0.1 to 2.2 and 0.9 to 3.2 µg L−1, respectively, indicating that the degradation products by themselves or in combination with parent atrazine can exceed the maximum contaminant level (mcl) of 3 µg L−1 even though atrazine by itself may be &lt;3 µg L−1. The deethylatrazineto‐atrazine ratio (DAR) is an indicator of residence time in soil during transport of atrazine to groundwater. In Plots 2 and 4, DAR values for tile‐drain water ranged from 0.43 to 2.70 and 0.50 to 2.66, respectively. By comparison, a DAR of 0.38 to 0.60 was observed in Plot 5, suggesting less residence time in the soil.

Integrated Soil, Crop and Water Management System to Abate Herbicide and Nitrate Contamination of the Great Lakes

Corn management practices, incorporating annual ryegrass intercrop, conservation tillage and water table management, were evaluated to reduce herbicide and N0−3 losses through surface runoff and tile drainage. The integrated management system being developed at Harrow in S.W. Ontario reduced herbicide input 50% by banding the chemical over the seed row. Runoff events close to herbicide application contained high concentrations of atrazine, metribuzin and metolachlor. However, the volume of runoff was low during the 1991 growing season, therefore herbicide loss was low (&amp;lt;2% of applied). The three herbicides rapidly dissipated in the soil so that subsequent runoff events transported little herbicide in the runoff water. The total quantity of de-ethyl atrazine loss was lower from soil saver than moldboard plow. No water table control or intercrop effects were found in 1991 for herbicide loss because of the drought Tile drainage resulted in a greater volume of water and loss of N0−3 than with surface runoff. Consequently, over 97% of the total N0−3 loss occurred through tile drainage. The flow weighted N0−3 concentration in tile drainage water was 22.5 mg N L−1 for the drainage treatments and 15.1 mg N L−1 for the water table control treatments from Nov. 1, 1991 till April 30, 1992. During this time period, N0−3 loss through tile drainage was 57.8 kg N ha−1 from the drainage treatments and 36.3 kg N ha−1 from the water table control treatments. Therefore, the water table control treatment reduced the flow weighted N0−3 concentration in tile drainage water by 33% and total N0−3 loss by 37%. The water table control treatments combined with soil saver tillage resulted in lower concentrations and losses of N0−3 than with any other treatments.

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.

Surface and subsurface transport of atrazine and alachlor from a Brookston clay loam under continuous corn production

Three tillage practices, conventional, zero, and ridge tillage, were compared for water quality in the first three years of tillage establishment. The tillage treatments were on a poorly drained, Brookston clay loam soil of <1% slope, tiled to a depth of 95 cm. Tillage had no significant effect on runoff volume, distribution between surface and subsurface runoff, herbicide concentration or herbicide loss. The volume of tile discharge exceeded the volume of surface runoff in all years. Triazine losses varied from 1.2 to 7.7% of atrazine applied (1.8 kg/ha) while alachlor losses were less than 0.5% of application (2.5 kg/ha). Herbicide losses were greatest when runoff producing events occurred soon after herbicide application. The dealkylated metabolite, de-ethyl atrazine, was detected in the runoff water at low concentrations throughout the study period consistent with its occurrence as an intermediate metabolite. Herbicide concentrations were higher in surface runoff water than subsurface runoff water which resulted in a greater proportion of herbicide loss from the surface. In most cases more atrazine was lost during the growing season that at other times, however, in drier years losses after harvest may account for a significant proportion of total loss. In all years, alachlor losses occurred during the growing season, because of its shorter persistence in soil relative to atrazine.

Degradation and bound residue formation of atrazine in a Western Tennessee soil

Biological and physical degradation, and metabolite and soil-bound residue formation, of [U-ring-14C]atrazine (2-chloro-4-[ethylamino]-6-[isopropylamino]-1,3,5-triazine) were characterized in a western Tennessee soil using laboratory and field assays. Biological mineralization of [14C]atrazine was examined in the laboratory using intact surface soil cores in sealed microcosms. Physical mineralization was determined using gamma-radiation-sterilized soil microcosms. Metabolites measured were deethylatrazine (DEA), deisopropylatrazine (DIA), dealkylatrazine (DAA) and hydroxyatrazine (HYA). Atrazine was applied at a rate of 2.2 kg/ha (˜ 5.6 μg/g soil) to soil microcosms in two studies and 3.2 kg/ha to the field. Evolution of 14CO2 from [14C]atrazine in nonirradiated soil microcosms increased to 12 and 28% of the radiolabel added after 180 d incubation. Irradiated soil microcosms evolved less than 0.07% of the radiolabel as 14CO2 for both studies after the same period. The concentrations of metabolites throughout the laboratory and field studies were: HYA > DEA > DIA > DAA. The highest concentration of HYA detected during microcosm and field studies was approximately 0.5 μg/g soil. Atrazine dissipation rates and metabolite production in nonirradiated microcosms were comparable to field results. Atrazine concentrations after 180 d in nonirradiated microcosm and field samples were lower than HYA, and either equivalent to or greater than DEA. The DAA was not detected throughout microcosm or field studies. Rates of dissipation for atrazine followed first-order kinetics. Atrazine half-life, based on extractable residues, was approximately 21 d in the microcosm studies, compared to 14 d in surface field soil. Extractable 14C residues sampled from nonirradiated microcosms decreased in concentration during the incubation period. Soil-bound 14C residues increased and, at the termination of the two studies, accounted for 39 and 43% of the radioactivity added to nonirradiated microcosms. Bound 14C residues in irradiated microcosms accounted for 49 and 48% of the activity after 180 d. Similarity of results between microcosm and field studies suggests that those microcosms may be useful for predicting the fate of atrazine in surface soil.