Deethylatrazine Concentrations Research Articles

Occurrence of Banned and Currently Used Herbicides, in Groundwater of Northern Greece: A Human Health Risk Assessment Approach.

The presence of pesticide residues in groundwater, many years after their phase out in European Union verifies that the persistence in aquifer is much higher than in other environmental compartments. Currently used and banned pesticides were monitored in Northern Greece aquifers and a human health risk assessment was conducted. The target compounds were the herbicides metolachlor (MET), terbuthylazine (TER), atrazine (ATR) and its metabolites deisopropylatrazine (DIA), deethylatrazine (DEA) and hydroxyatrazine (HA). Eleven sampling sites were selected to have representatives of different types of wells. Pesticides were extracted by solid-phase extraction and analyzed by liquid chromatography. MET was detected in 100% of water samples followed by ATR (96.4%), DEA and HA (88.6%), DIA (78.2%) and TER (67.5%). ATR, DIA, DEA, HA, MET and TER mean concentrations detected were 0.18, 0.29, 0.14, 0.09, 0.16 and 0.15 μg/L, respectively. Obtained results were compared with historical data from previous monitoring studies and temporal trends were assessed. Preferential flow was the major factor facilitating pesticide leaching within the month of herbicide application. Moreover, apparent age of groundwater and the reduced pesticide dissipation rates on aquifers resulted of long-term detection of legacy pesticides. Although atrazine had been banned more than 18 years ago, it was detected frequently and their concentrations in some cases were over the maximum permissible limit. Furthermore, human health risk assessment of pesticides was calculated for two different age groups though drinking water consumption. In all examined wells, the sum of the HQ values were lower than the unity. As a result, the analyzed drinking water wells are considered safe according to the acute risk assessment process. However, the presence of atrazine residues causes concerns related with chronic toxicity, since ATR R values were greater than the parametric one of 1 × 10−6 advised by USEPA, for both age groups.

Thirty-year monitoring of s-triazine herbicide contamination in the aquifer north of Vicenza (north-east Italy)

The aquifer north of Vicenza, Italy, is one of the main and most studied drinking water reservoirs within the Veneto region. The area is an intensive cropland, and monitoring of s-triazine herbicides and metabolites has been carried out since the late eighties. This study analysed the trends of atrazine (ATR), terbuthylazine (TBZ), deethyl-atrazine (DEA), and deethyl-terbuthylazine (DET) concentrations from 1987 to 2016 and related the variations of agricultural land use, herbicide load, and pesticide regulations to the residence time of pollutants in the aquifer. In total, 785 water samples collected from 82 selected check wells were analysed with high-resolution gas chromatography combined with mass spectrometry. Non-detects were substituted by one-half the limit of detection. Over the 30 years of monitoring, concentrations of all of the pollutants decreased at all sampling sites. Since the beginning, TBZ and DET residues have been systematically lower than ATR and DEA, respectively, with more than 70% of the data below the limit of detection and never exceeding the European Maximum Acceptable Concentration (MAC) for a single pesticide (0.1 μg/L). The highest concentrations of ATR and DEA showed a spatial shift along the flow direction, suggesting an increase in groundwater residence time from the recharge zone to the accumulation zone of the aquifer. The last residues of ATR were found 27 years after its ban.Although all of the concentrations were lower than those found elsewhere in Europe, the sum of s-triazines overcame the MAC in 20% of the samples. Considering the structural and toxicological similarities of s-triazines, these findings confirm the necessity of better characterisation of the toxicological risk posed by mixtures.

Factors controlling spatial and temporal patterns of multiple pesticide compounds in groundwater (Hesbaye chalk aquifer, Belgium)

Factors governing spatial and temporal patterns of pesticide compounds (pesticides and metabolites) concentrations in chalk aquifers remain unclear due to complex flow processes and multiple sources. To uncover which factors govern pesticide compound concentrations in a chalk aquifer, we develop a methodology based on time series analyses, uni- and multivariate statistics accounting for concentrations below detection limits. The methodology is applied to long records (1996–2013) of a restricted compound (bentazone), three banned compounds (atrazine, diuron and simazine) and two metabolites (deethylatrazine (DEA) and 2,6-dichlorobenzamide (BAM)) sampled in the Hesbaye chalk aquifer in Belgium. In the confined area, all compounds had non-detects fractions >80%. By contrast, maximum concentrations exceeded EU's drinking-water standard (100 ng L−1) in the unconfined area. This contrast confirms that recent recharge and polluted water did not reach the confined area, yet. Multivariate analyses based on variables representative of the hydrogeological setting revealed higher diuron and simazine concentrations in the southeast of the unconfined area, where urban activities dominate land use and where the aquifer lacks protection from a less permeable layer of hardened chalk. At individual sites, positive correlations (up to τ=0.48 for bentazone) between pesticide compound concentrations and multi-annual groundwater level fluctuations confirm occurrences of remobilization. A downward temporal trend of atrazine concentrations likely reflects decreasing use of this compound over the last 28 years. However, the lack of a break in concentrations time series and maximum concentrations of atrazine, simazine, DEA and BAM exceeding EU's standard post-ban years provide evidence of persistence. Contrasting upward trends in bentazone concentrations show that a time lag is required for restriction measures to be efficient. These results shed light on factors governing pesticide compound concentrations in chalk aquifers. The developed methodology is not restricted to chalk aquifers, it could be transposed to study other pollutants with concentrations below detection limits.

Pesticides in Groundwater of the United States: Decadal‐Scale Changes, 1993–2011

The national occurrence of 83 pesticide compounds in groundwater of the United States and decadal-scale changes in concentrations for 35 compounds were assessed for the 20-year period from 1993-2011. Samples were collected from 1271 wells in 58 nationally distributed well networks. Networks consisted of shallow (mostly monitoring) wells in agricultural and urban land-use areas and deeper (mostly domestic and public supply) wells in major aquifers in mixed land-use areas. Wells were sampled once during 1993-2001 and once during 2002-2011. Pesticides were frequently detected (53% of all samples), but concentrations seldom exceeded human-health benchmarks (1.8% of all samples). The five most frequently detected pesticide compounds-atrazine, deethylatrazine, simazine, metolachlor, and prometon-each had statistically significant (p < 0.1) changes in concentrations between decades in one or more categories of well networks nationally aggregated by land use. For agricultural networks, concentrations of atrazine, metolachlor, and prometon decreased from the first decade to the second decade. For urban networks, deethylatrazine concentrations increased and prometon concentrations decreased. For major aquifers, concentrations of deethylatrazine and simazine increased. The directions of concentration changes for individual well networks generally were consistent with changes determined from nationally aggregated data. Altogether, 36 of the 58 individual well networks had statistically significant changes in concentrations of one or more pesticides between decades, with the majority of changes attributed to the five most frequently detected pesticide compounds. The magnitudes of median decadal-scale concentration changes were small-ranging from -0.09 to 0.03 µg/L-and were 35- to 230,000-fold less than human-health benchmarks.

Temporal evolution of atrazine, metolachlor, and deethylatrazine concentrations in runoff from grass filter strips in a four-season study

<h3>BACKGROUND:</h3> There has not been a detailed description of expiratory reserve volume (ERV) during slow expiration with glottis open in infralateral decubitus position (ELTGOL, for Expiration Lente Totale Glotte Ouverte en infraLatéral) and its reproducibility. The aim of this study was to determine ERV during ELTGOL and to evaluate ERV intra-observer and inter-observer reliability. <h3>METHODS:</h3> In this prospective study, subjects were 30–70 y of age with chronic lung disease. ELTGOL (an active-passive or active physiotherapy technique) was applied in random order by 3 observers: 2 trained physiotherapists (PT 1 and PT 2) and the subject him/herself. Two ELTGOL compressions (A and B) were applied by PT 1, PT 2, and the subject. <h3>RESULTS:</h3> Thirty-two subjects were evaluated with moderate lung obstruction, FEV₁: 47.7 ± 15.4, and ERV: 61.7 ± 29.4. The mean value of ERV for PT 1 was 51.4 ± 24.8%; for PT 2, it was 54.3 ± 31.8%; and for the subject, it was 53.5 ± 26.2% (<i>P</i> = .49). Considering the mean value of ERV, the ELTGOL mobilized more than 80% of ERV. There was good reliability intra-PT: PT 1, intraclass correlation coefficient (ICC) 0.85 (0.70–0.93), <i>P</i> &lt; .0001; PT 2, ICC 0.90 (0.80–0.95), <i>P</i> &lt; .0001, and inter-PT (ICC 0.86 [95% CI 0.71–0.93], <i>P</i> &lt; .001). The Bland-Altman plot with mean bias and limits of agreement for ERV of PT 1 and PT 2 was −3.3 (−42.7 to 35.9). <h3>CONCLUSIONS:</h3> ELTGOL mobilized more than 80% of ERV in subjects with moderate airway obstruction; there is no difference in ERV exhaled during the technique applied by a physiotherapist or by the subject. ELTGOL is a reproducible technique, determined by inter- and intra-observer testing.

Impact of vegetated filter strips on sorbed herbicide concentrations and sorption equilibrium in agricultural plots

The objective was to investigate the impact of vegetated filter strips on exported atrazine and deethylatrazine concentrations [dissolved and sorbed to eroded sediments (>1.5 μm)], the deethylatrazine to atrazine ratio in water and sediments, the ratio of sorbed to dissolved herbicides in runoff and subsurface infiltration as well as field equilibrium state under natural climate during two seasons. We hypothesize that sorption equilibrium was not achieved in 2004 because of the short delay (<24 h) between herbicide application and the first rain event. In 2005, observations suggest that possible changing sorption equilibrium conditions were reached (20 days after atrazine application), especially for eroded sediments submitted to changing environmental conditions in subsurface. If confirmed by other experiments, this will raise the question of the representativeness of laboratory-determined soil sorption coefficients to predict the fate of pesticides.

Temporal evolution of atrazine and metolachlor concentrations exported in runoff and subsurface water with vegetated filter strips

Metolachlor and atrazine are herbicides used in corn agriculture and detected in surface- and groundwater. Vegetated filters reduce masses of herbicides in runoff, but less attention has been given to their impact on degradation products and subsurface infiltrated water. The objective was to study the temporal evolution of dissolved metolachlor, atrazine and deethylatrazine concentrations in runoff and subsurface infiltrated water with two types of vegetated filters over 2 years for the first three rains following herbicide application. Runoff and subsurface infiltrated at 90-cm water samples from 12 plots of 30 × 5 m in a completely randomized block design of four replicates of three treatments-control without filter, 5-m-long grass filter, 5-m-long grass and tree filter were analysed using gas chromatography/mass spectrometry. Controls in runoff generally had the highest average atrazine, as high as 739 μg L−1, and metolachlor average concentrations, as high as 1,725 μg L−1. The first rain after application was mainly responsible for atrazine and metolachlor exports. Vegetated filters reduced concentrations of atrazine and metolachlor in runoff below their respective Canadian criterion of 1.8 μg L−1 for atrazine and 7.8 μg L−1 for metolachlor (provisory) (CCME 2002) for the protection of aquatic life when rain did not occur shortly after application. With the need to increase food production and agricultural yields to sustain the increasing world population came the need to develop efficient mitigation tools such as vegetated filter strips to reduce the ecotoxicologial impacts of pesticides. The present study is among the few that examined herbicide degradation products and subsurface infiltrated water under filter strips in order to provide new knowledge on the relationship between herbicide loss pathways and the environmental benefits of these strips. Such knowledge will provide much needed information to modellers, decision makers, ecotoxicologists and agronomists involved in the regulation, design and implementation of vegetated filter strips for the protection of water quality.

Trends of Pesticides and Nitrate in Ground Water of the Central Columbia Plateau, Washington, 1993–2003

Pesticide and nitrate data for ground water sampled in the Central Columbia Plateau, Washington, between 1993 and 2003 by the U.S. Geological Survey National Water-Quality Assessment Program were evaluated for trends in concentration. A total of 72 wells were sampled in 1993-1995 and again in 2002-2003 in three well networks that targeted row crop and orchard land use settings as well as the regional basalt aquifer. The Regional Kendall trend test indicated that only deethylatrazine (DEA) concentrations showed a significant trend. Deethylatrazine concentrations were found to increase beneath the row crop land use well network, the regional aquifer well network, and for the dataset as a whole. No other pesticides showed a significant trend (nor did nitrate) in the 72-well dataset. Despite the lack of a trend in nitrate concentrations within the National Water-Quality Assessment dataset, previous work has found a statistically significant decrease in nitrate concentrations from 1998-2002 for wells with nitrate concentrations above 10 mg L(-1) within the Columbia Basin ground water management area, which is located within the National Water-Quality Assessment study unit boundary. The increasing trend in DEA concentrations was found to negatively correlate with soil hydrologic group using logistic regression and with soil hydrologic group and drainage class using Spearman's correlation. The decreasing trend in high nitrate concentrations was found to positively correlate with the depth to which the well was cased using logistic regression, to positively correlate with nitrate application rates and sand content of the soil, and to negatively correlate with soil hydrologic group using Spearman's correlation.

Decadal‐Scale Changes of Pesticides in Ground Water of the United States, 1993–2003

Pesticide data for ground water sampled across the United States between 1993-1995 and 2001-2003 by the U.S. Geological Survey National Water-Quality Assessment Program were evaluated for trends in detection frequency and concentration. The data analysis evaluated samples collected from a total of 362 wells located in 12 local well networks characterizing shallow ground water in agricultural areas and six local well networks characterizing the drinking water resource in areas of variable land use. Each well network was sampled once during 1993-1995 and once during 2001-2003. The networks provide an overview of conditions across a wide range of hydrogeologic settings and in major agricultural areas that vary in dominant crop type and pesticide use. Of about 80 pesticide compounds analyzed, only six compounds were detected in ground water from at least 10 wells during both sampling events. These compounds were the triazine herbicides atrazine, simazine, and prometon; the acetanilide herbicide metolachlor; the urea herbicide tebuthiuron; and an atrazine degradate, deethylatrazine (DEA). Observed concentrations of these compounds generally were < 0.12 microg L(-1). At individual wells, changes in concentrations typically were < 0.02 microg L(-1). Data analysis incorporated adjustments for changes in laboratory recovery as assessed through laboratory spikes. In wells yielding detectable concentrations of atrazine, DEA, and prometon, concentrations were significantly lower (alpha = 0.1) in 2001-2003 than in 1993-1995, whereas detection frequency of these compounds did not change significantly. Trends in atrazine concentrations at shallow wells in agricultural areas were found to be consistent overall with recent atrazine use data.

Improved GC‐MS/MS Method for Determination of Atrazine and Its Chlorinated Metabolites in Forage Plants—Laboratory and Field Experiments

Analytical procedures using gas chromatography–ion trap tandem mass spectrometry (GC‐MS/MS) were developed to analyze atrazine (ATR) and its dealkylated metabolites in four forage species (switchgrass, tall fescue, smooth bromegrass, and orchardgrass). Atrazine, deethylatrazine (DEA), and deisopropylatrazine (DIA) were extracted with methanol (CH3OH) followed by liquid–liquid extraction and partitioning into chloroform, with additional cleanup by C18 solid‐phase extraction (SPE). Through the optimization of ionization conditions and ion storage voltages, the background noise of product ion spectra (MS/MS) was reduced dramatically, providing sub‐µg/kg detection limits. Mean recoveries of ATR, DEA, and DIA were 94.3, 105.6, and 113.1%, respectively. The estimated limit of detection (LOD) was 0.6 µg/kg for ATR, 1.3 µg/kg for DEA, and 0.3 µg/kg for DIA. These LODs were one to two orders of magnitude lower than those reported for other GC‐MS, GC‐MS/MS, high pressure liquid chromatography (HPLC)‐UV, or HPLC‐MS/MS procedures designed for food‐safety monitoring purposes. To validate the developed method, a field experiment was carried out utilizing three replications of four forage treatments (orchardgrass, tall fescue, smooth bromegrass, and switchgrass). Forage plants were sampled for analyses 25 days after atrazine application. DEA concentrations in C3 grasses ranged from 47 to 96 µg/kg, about 10‐fold higher than in switchgrass, a C4 species. The ATR and DIA concentrations were similar, ranging from 1.5 to 13.2 µg/kg. The developed method provided sufficient sensitivity to determine the fate of ATR and its chlorinated metabolites via plant uptake from soil or dealkylation within living forage grasses. It also represented significant improvements in sensitivity compared to previous GC methods.

Pesticides in the groundwater of a spring draining a sandy aquifer: Temporal variability of concentrations and fluxes

A 250 ha agricultural catchment has been characterized with respect to its hydrogeology and groundwater contamination by pesticides from October 1999 to August 2004. Five years after the ending of atrazine (At) application, used since the sixties, At and deethylatrazine (DEA) are still systematically quantified at the outlet of the watershed with concentrations from 0.07 to 0.43 μg l − 1 for At, and between 0.14 and 1.16 μg l − 1 for DEA. Isoproturon and chlortoluron are detected in only one (0.3 μg l − 1 ) and two (0.7 and 2.0 μg l − 1 ) of the 124 semi-monthly samples, respectively. DEA concentrations can be very different between two samples with a 15-day time step. The annual mean exported fluxes of cumulated At and DEA are stable, which indicates a long time transfer in the unsaturated or saturated zone with a progressive leaching of the stock of At and DEA probably accumulated in the soil and the vadose zone. These fluxes, between 0.90% and 2.82% of the annual mean dose of At applied before 1999, similar to those calculated in several studies at the bottom of the root zone, could be explained by low adsorption and degradation properties of At and DEA in the unsaturated and saturated zone.

Montmorillonite as an adsorbent for extraction and concentration of atrazine, propazine, deethylatrazine, deisopropylatrazine and hydroxyatrazine

Adsorption properties of the clay mineral montmorillonite in the potassium homoionic form (KMT) was investigated to achieve the extraction and concentration of the herbicides atrazine (AT) and propazine (PROP), as well as the main degradation products of atrazine, namely deethylatrazine (DEA), deisopropylatrazine (DIA) and hydroxyatrazine (ATOH). A batch approach was proposed, with recovery percentages for AT, PROP and DIA higher than 90% at concentrations of 0.50 and 2.50 μg L −1. For DEA and ATOH, however, low recoveries were obtained. For DEA, this fact can be explained by its low K d with KMT, contrary to ATOH, which interacts strongly with the mineral surface, hindering the complete desorption and hence, generating low recovery percentages. The influence of pH, ionic strength and humic acid was studied, and a comparison with the C 18 phase as SPE cartridges was carried out. Montmorillonite showed a similar performance to commercial cartridge for concentrations of AT, DEA and PROP, but better recoveries for DIA was obtained using the clay mineral. For ATOH the recovery was also higher on the clay mineral, although for this compound the most suitable SPE cartridge is constituted by cation exchange resin. After the concentration and elution steps, the 0.50 and 2.50 μg L −1 gave chromatographic peak areas that could be easily quantified with an analytical curve obtained in the concentration range between 7.5 and 100 μg L −1. The obtained concentration factors are suitable to allow the application of the method to the monitoring of triazine residues in drinking water.

The Attenuation of Atrazine and its Major Degradation Products in a Restored Riparian Buffer

The fate and transport of atrazine and three of its major degradation products were studied in a restored forested riparian buffer system in southern Georgia to examine the effectiveness of the system in attenuating the chemicals. Atrazine was applied to a 10 100 m strip immediately upslope from the buffer system, and atrazine, deethylatrazine, deisopropylatrazine, and hydroxyatrazine were monitored in groundwater, soil, and runoff water for 11 months following application. Atrazine removal from groundwater was very effective, with the calculated 3810 mg entering the upslope position being reduced to 174 mg exiting the streamside landscape position. Each of the landscape positions (0, 8, 13, 18, 28, and 38 m from the application strip) in the buffer system contributed significantly to the atrazine concentration reduction in the initial three months following application, when the majority of atrazine was measured. Deethylatrazine is the primary result of biotic degradation and was the predominant degradation product in groundwater, with approximately 10% (379 mg) as much estimated to have entered the upper interface of the buffer system as did the parent atrazine. The riparian buffer system was successful in significantly reducing concentrations of deethylatrazine in groundwater in both the initial three months following application and in the final eight months of the study. Adsorption of the analytes to subsurface soils was minimal in this system. Deethylatrazine was also the predominant degradation product in the runoff water, but hydroxyatrazine was predominant in conjunction with runoff sediments. Removal efficiency of analyte mass loads in surface runoff water ranged from 92% to 100% as the chemicals were transported through the buffer system. While the mass load of atrazine associated with sediment was only 8% of that measured for the water phase, the mass loads of deethylatrazine and deisopropylatrazine (approximately 40%) and particularly hydroxyatrazine (75%) in sediments were proportionally much higher. About 98.6% of measured runoff water and sediment phase transport of atrazine occurred within the first few days following application as a result of an extended rainfall event. In contrast, roughly 45% of the deethylatrazine and deisopropylatrazine and only 16% of the hydroxyatrazine were measured in the first rain event sample. The results of this work indicate that riparian buffer systems can be successfully used to intercept atrazine and the studied degradation products in order to minimize contamination of natural water systems. Riparian buffers can provide year round attenuation, particularly for deethylatrazine. The importance of timing atrazine application to correspond with periods when there is no threat of rainfall is also emphasized.

Seasonal exposures to triazine and other pesticides in surface waters in the western Highveld corn-production region in South Africa

The objective of this study was to characterize concentrations of atrazine, terbuthylazine, and other pesticides in amphibian habitats in surface waters of a corn-production area of the western Highveld region (North-West Province) of South Africa. The study was conducted from November 2001 to June 2002, coinciding with the corn-production season. Pesticide residues were measured at regular intervals in surface water from eight ponds, three in a non-corn-growing area (NCGA) and five within the corn-growing area (CGA). Measured atrazine concentrations differed significantly among sites and between samples. In the five CGA sites, the maximum atrazine concentrations measured during the study ranged from 1.2 to 9.3 μg/L. Although no atrazine was recorded as being applied in the catchment of the three NCGA sites, maximum concentrations from 0.39 to 0.84 μg/L were measured during the study, possibly as a result of atmospheric transport. Maximum measured concentrations of terbuthylazine ranged from 1.22 to 2.1 μg/L in the NCGA sites and from 1.04 to 4.1 μg/L in the CGA sites. The source of terbuthylazine in the NCGA sites may have been in use other than in corn. The triazine degradation products, deisopropylatrazine (DIA) and deethylatrazine (DEA) and diaminochlorotriazine (DACT) were also found in water from both the CGA and NCGA sites. Concentrations of DIA were ≥1 μg/L throughout the season, while DEA concentrations were mostly <0.5 μg/L before planting but increased after planting and application of herbicides to concentrations >2 μg/L in some locations. Concentrations of DACT were highly variable (LOD to 8 μg/L) both before and after planting and application, suggesting that they resulted from historical use of triazines in the area. Other herbicides such as simazine and acetochlor were only detected infrequently and pesticides such as S-metolachlor, cypermethrin, monocrotophos, and terbuphos, known to be used in the CGA, were not detected in any of the samples. Because of dilution by higher than normal rainfall in the study period, these concentrations may not be predictive of those in years of normal rainfall.

Atrazine, deethylatrazine, and deisopropylatrazine in surface runoff from conservation tilled watersheds.

Atrazine and two of its metabolites, deethylatrazine (DEA) and deisopropylatrazine (DIA), are frequently detected in surface runoff. Although their health and environmental effects may be similar to that of atrazine and ratios of their concentrations are useful in delineating sources of contamination, there have been few long-term studies of the factors affecting their losses in runoff. Therefore, losses of atrazine, DEA, and DIA were monitored for six years in runoff from seven small (0.45-0.79 ha) watersheds under three tillage practices. Weather year and the timing of runoff-producing rainfall had a greater effect on atrazine, DEA, and DIA concentrations and losses than did tillage practice. DEA was the most frequently detected metabolite with an average concentration in the year of atrazine application, of 2.5 microg L(-1) compared to 0.7 microg L(-1) for DIA. Atrazine exceeded its 3 /g L(-1) maximum contaminant level (MCL) up to 100 days after application. DEA and DIA exceeded the atrazine MCL up to 50 days after atrazine application; thus, failure to monitor their presence may result in underestimation of the environmental impact of atrazine usage. The molar concentration ratio of DEA to atrazine (DAR) was affected by tillage treatment, weather year, and possibly soil type. These factors may need to be taken into account when DAR is used as an index of atrazine movement. The ratio of DIA to DEA (D2R) was fairly constant and should be useful in determining the parent compounds contributing DIA to surface waters.

AGRICHEMICAL TRANSPORT TO GROUNDWATER THROUGH COASTAL PLAIN SOILS

A 1ha field with Pine Flat loamy sand (coarseloamy, siliceous, thermic Typic Paleudult) and Troup loamy sand(loamy, siliceous, thermic Grossarenic Kandiudult) surface soils, located near Plains, Georgia, was studied for four years(1993 to 1996) to evaluate potential agrichemical transport to groundwater. The field was managed to produce summer cornand winter wheat. Commercial fertilizer, the herbicide atrazine, and the insecticide carbofuran were applied to the field in1993, 1994, and 1995. Average annual application rates were 266 kg nitrogen ha1, 2.5 kg atrazine ha1, and 2.4 kgcarbofuran ha1. Monthly soilwater and groundwater samples were collected. The samples were analyzed for nitratenitrogen (NO3N), chloride, atrazine, carbofuran, and deethylatrazine (DEA). Soilwater and groundwater samplesindicated elevated NO3N concentrations (>5 ppm) in the vadose zone at 4.3 m and in the aquifer at 10 m (>4 ppm). Of thestudied pesticides, carbofuran and DEA were observed at the greatest concentrations in groundwater.<br><br>Both NO3N and pesticides were transported during groundwater recharge following periods of excess precipitation.Peak pesticide concentrations in groundwater were observed in late 1994, driven by a large precipitation event in July of 1994when 565 mm of rain fell over a 4day period. Atrazine and carbofuran concentrations in groundwater did not exceed theEPA maximum contaminant levels of 3 ppb and 40 ppb, respectively. Spatially averaged concentrations observed in monthlygroundwater collected directly below the field were well below these standards. Concentrations of NO3N, atrazine, DEA,and carbofuran observed in groundwater from the onfield wells were significantly different from upgradient anddowngradient concentrations (p = 0.05). These data indicate a significant impact to the local groundwater. Nitrate N wastransported downgradient from the field at the largest concentrations. Peak concentrations of atrazine and DEA weresimultaneously observed in the groundwater, indicating similar transport rates for both compounds and rapid transformationfrom atrazine into DEA in the rootzone.

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.

Groundwater Quality under Conventional and No Tillage: II. Atrazine, Deethylatrazine, and Metolachlor

AbstractThe effect of no tillage (NT) and conventional tillage (CT) on the contamination of shallow groundwater by atrazine (2‐chloro‐4‐ethylamino‐6‐isopropylamino‐s‐triazine), deethylatrazine (2‐chloro‐4‐amino‐6‐isopropylamino‐s‐triazine), and metolachlor (2‐chloro‐N‐(ethyl‐6‐methylphenyl)‐N‐(2‐metoxy‐1‐methylethyl) acetamide) at nominal depths of 1.2, 1.8, 3.0, and 4.6 m was studied during four successive crop‐years in four corn (Zea mays L.) fields with loam soil. Atrazine and deethylatrazine were almost always present in the shallow groundwater. Atrazine concentrations were below the U.S. Environmental Protection Agency (USEPA) lifetime health advisory (LHA) of 3 µg/L in more than 99% of the 920 groundwater samples from the two tillage treatments. Atrazine concentrations, although low, were significantly higher under NT than CT (P &lt; 0.05) at the 1.8 and 3.0 m depths. Deethylatrazine concentrations were also low but were generally higher than those of the parent compound. They were significantly higher under NT than CT at the 1.2 and 1.8 m depths (P &lt; 0.1), as well as at 3.0 m (P &lt; 0.01). Metolachlor was detected in only 25% of the samples and concentrations were well below the USEPA LHA of 100 µg/L. There was no tillage treatment effect on metolachlor concentration. Results from this study suggest a low potential for serious pollution of shallow groundwater from application of atrazine and metolachlor at agronomically recommended rates in tile‐drained corn fields in cold humid regions under both CT and NT practices. However, atrazine leaching appears to be greater under NT than under CT.

Impact of roots on ground water quality

Preferential flow is perhaps the major chemical transport process influencing the rapid and typically unexpected movement of agricultural chemicals to ground water. Plant roots are a major contributor to preferential flow mechanics as they form spatial voids which can be used as preferential flow pathways. Chemical transport of atrazine, deethylatrazine, and bromide solutions concentrations under tilled and no-tilled corn fields was evaluated below the active root zone. Additionally, the impact of roots on flow pathways was visualized using a soluble dye (Brilliant Blue FCF). Pictures of the dye-stained pattern were subsequently digitized to determine the cross-sectional area used for transport as a function of depth. Bromide transit times through the field soils were not influenced by tillage practice, whereas atrazine transport was strongly influenced by tillage practice. Under no-till field conditions, atrazine was rarely detected but deethylatrazine concentrations were greater than those observed under tilled field conditions. Visual observation indicated that the dye under no-tillage was more predominant in the corn row, indicative of transport through void root channels. No-tillage practices may decrease the likelihood of ground water contamination through leaching due to the formation of stable root channels where an organic carbon source and microbial population are preferentially located to degrade pesticides.

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.