El objetivo de este trabajo es comparar y evaluar los resultados que brindan cinco metodologías de evaluación de vulnerabilidad del acuífero en un área de actividad agrícola intensiva en el SE bonaerense. El área de estudio es la Cuenca del Arroyo de Los Padres, donde el acuífero Pampeano es la única fuente de agua. Las metodologías utilizadas son EKv, GOD/GOD-S y DRASTIC/DRASTIC-P. La evaluación de la vulnerabilidad del acuífero se realizó en entorno ArcGis 10.1. En general, se observó que las zonas más vulnerables coinciden con las zonas bajas de la cuenca, mientras que las zonas menos vulnerables se encuentran en las zonas altas. El método EKv identifica más del 75% del área de estudio como de “vulnerabilidad moderada”, siendo el menos restrictivo y adecuado para una primera aproximación. Las metodologías GOD y GODS muestran un área extensa de "baja vulnerabilidad", destacándose que GODS muestra una vulnerabilidad baja en el 96% del territorio. DRASTIC y DRASTIC-P muestran mayores áreas de "alta vulnerabilidad", siendo estas metodologías las que utilizan más variables y proporciona resultados más confiables y cercanos a la realidad. En resumen, los métodos DRASTIC y DRASTIC-P son más útiles para la toma de decisiones y la protección del acuífero, ya que consideran parámetros importantes relacionados con su vulnerabilidad. Estos métodos proporcionan un mejor equilibrio entre incertidumbre y utilidad en la toma de decisiones.

El objetivo del presente trabajo consistió en evaluar el peligro de contaminación del agua subterránea asociado al uso de plaguicidas, considerando sus propiedades, las del suelo donde son aplicados y las del acuífero al cual potencialmente pueden lixiviar. La zona de estudio considerada fue la cuenca del río Quequén Grande donde la única provisión de agua es el acuífero Pampeano y la agricultura la actividad dominante. Se trabajó en entorno ARCGIS y el peligro de contaminación se obtuvo por la combinación de la vulnerabilidad del acuífero (índice DRASTIC) y la carga contaminante potencial (índice AFT). El mapa de vulnerabilidad mostró que los sectores menos vulnerables se ubican en la zona alta de la cuenca y los de mayor en la zona baja. Cinco plaguicidas fueron clasificados con una categoría superior a “poco probable lixiviación”, con las mayores cargas contaminantes en el sector alto. Se obtuvieron dos mapas de peligro, con las zonas de menor peligro en la zona NE, debido al nivel freático más profundo y mayor porcentaje de materia orgánica. Las zonas de mayor peligro se ubican en el sector O y SE, debido a menores contenidos de materia orgánica, bajos espesores del horizonte A y un nivel freático más somero. Estos mapas obtenidos pueden ser utilizados entonces en la gestión del hídrico subterráneo: si la carga contaminante es baja, se considera suficiente el uso de los mapas obtenidos según el índice AFT. Por el contrario, en aquellos casos que la carga sea mayor, se debe contemplar el uso de los mapas de peligrosidad.

This work evaluates the groundwater contamination hazard associated with the use of pesticides, considering their properties, the soil where they are applied and the aquifer to which they can potentially leach. The study area considered was the Quequ??n Grande River basin where the only water supply is the Pampeano aquifer and agriculture is the dominant activity. The contamination hazard was obtained by combining the aquifer vulnerability (DRASTIC index) and the potential pollutant load (AFT index) working whit ARCGIS software. The sectors with the least vulnerability were in the upper zone of the watershed and those with the greatest vulnerability in the lower zone. Five pesticides were classified with a category higher than ???unlikely leaching???, obtaining the highest potential pollutant loads in the upper sector. Two hazard maps were obtained. In both, the least hazard areas are located in the north-east, where the water table is deeper, and the percentage of organic matter is higher. The areas of greatest hazard are in the west and southeast due to the shallow water level, lower content of organic matter, and low thickness of the A horizon. These maps obtained can then be used in groundwater management: if the contaminant load is low, the use of the maps obtained according to the AFT index is considered sufficient. On the contrary, in those cases where the load is greater, the use of hazard maps should be considered.

Glyphosate-based products are among the most important herbicides applied to enhance the production of food commodities, leading to the worldwide spread of this herbicide. The main goal of this work was to evaluate the off-site transport of glyphosate in a runoff experiment. A micro-plot experiment was conducted to assess the retention, leaching and runoff of glyphosate under rainfall simulation. Glyphosate losses due to spray drift were estimated. Concentrations of glyphosate and AMPA were determined in rainwater and subsurface soil from agricultural and riparian zones. Analyses were performed with UHPLC-MS/MS. Experimental results demonstrated that 88.1% of the applied glyphosate was retained in the surface soil layer (0-9 cm). Glyphosate leaching was negligible compared to its runoff (3.9%) and spray drift (6.9%). Thus, the risk of groundwater pollution would be lower in comparison to that of both surface waters and rainwater. Moreover, under field conditions, glyphosate and AMPA were detected in 52% of the rainwater samples and glyphosate was detected up to 1 m in both soil profiles. Although the experimental application was made with hand-held knapsack under low wind condition to minimize glyphosate aerial dispersion, the spray drift was the main source of glyphosate off-site transport, degrading air quality and rainwater for human consumption. The balance among spray drift, runoff and soil absorption of glyphosate when it was sprayed close to the soil surface (hand held equipment), demonstrated the importance of spray drift in mass balance studies during runoff and leaching experiments with glyphosate. (C) 2019 Elsevier Ltd. All rights reserved.

Pesticides are usually used in modern agriculture; however, their off-site migration and detrimental effects on terrestrial biota and nearby surface water environment are of great concern. Organochlorine pesticides (OCPs) can be found in different environmental matrices due to their persistence, representing a persistent pollution source. Soil (0–35 cm), terrestrial organisms (micro- and macro-invertebrates) and stream water samples were analysed to assess OCPs’ uptake by terrestrial invertebrates and OCPs’ levels in their surrounding environment. The study area involved agricultural plots from the Pampas area (Argentina) and the sampling was carried out during summer coincident with the pesticides application period. Although OCPs have been banned in Argentina, the concentration of OCPs in soils increased during the pesticide application period (2.8 ng g−1) in comparison with the pre-application period (0.3 ng g−1). It would be probably as a result of a flooding event, and a consequent transport of legacy pesticides adsorbed to soils particles from neighbor agricultural areas. The OCPs were highly bioaccumulated in soil mesofauna (acari and collembolans: 260 μg g−1); therefore the high sensitivity to external impact combined with their importance for ecosystem functions make soil mesofauna extremely valuable for monitoring programmes. In the aquatic environment, high endosulfan concentrations (227 ng L−1) were detected in stream water, being above the maximum limit for aquatic life protection. The different compositions of DDT, HCH, chlordane and endosulfan in all matrixes indicated that the residues of most compounds would be originated from historical application, and the implementation of long OCPs monitoring studies is highly recommended. As a whole, this study provides first results of OCPs levels in mesofauna of a typical intensive agricultural area from Argentina, and highlights the importance of soil mesofauna as a target group to understand the OCP migration process through the animal food chain.

Due to the increase in pesticide detection in groundwater and other environmental components, some indicators, such as the attenuation factor (AF) and the environmental impact quotient (EIQ), have been proposed to determine potential pesticide contamination. Thus, it is possible to select pest management strategies in order to minimize the risk of environmental impact. The objective of this work was to evaluate the potential groundwater contamination as well as the environmental impact due to pesticide use on the main crops within the Dulce creek basin (southeast Buenos Aires Province, Argentina). In the present study, 17 herbicides, 20 fungicides and 14 insecticides were selected. According to AF values, Imazetapir and Picloram herbicides, and Clothianidin insecticide were responsible for the greatest risk of groundwater contamination. Fungicides were classified as very immobile to moderately mobile, which determined an unlikely to highly unlikely risk of contamination potential tied to them. Results showed that herbicides would pose the greatest risk of potential groundwater contamination within the studied basin, followed by insecticides and finally by fungicides. Most pesticides showed a low EIQ, but the high number of applications of some of them, particularly in potatoes, significantly increased their dangerousness. Potato was the riskiest crop due to the high use of fungicides associated with its production. These results should be useful for the decision-making of the people or institutions related to the planning of the use of environmental resources in order to promote more sustainable forms of agricultural production.

Conyza sumatrensis y Conyza bonariensis son dos de las malezas mas problematicas en Argentina. En el sudeste bonaerense no existe informacion referida a la sensibilidad a glifosato de las especies de Conyza predominantes. El objetivo de este trabajo fue determinar la sensibilidad a glifosato y la dosis letal media en dos estados de desarrollo en las especies C. bonariensis y C. sumatrensis. Se realizo un ensayo con plantas en estadio de roseta y elongacion del tallo. En cada estadio se aplicaron dosis crecientes del herbicida glifosato (0, 0.5, 1, 2, 4, 8 y 12 L ha-1de producto formulado CREDIT 48%). Posteriormente se efectuaron evaluaciones visuales de control y se determino la biomasa aerea. Las curvas de dosis respuesta se ajustaron utilizando los modelos log-logistico y lineal plateau, ademas, se calculo la dosis requerida para alcanzar el 50% de control (EC50). En estadio de roseta, la EC50 fue de 1.37 y 1.12 L ha-1 en C. sumatrensis y C. bonariensis respectivamente, mostrando similar grado de tolerancia al herbicida. En estado de elongacion ambas especies presentaron mayores valores de EC50 (8.04 y 2.44 L ha-1 respectivamente). Los resultados demostraron que las especies de Conyza difieren en su respuesta al herbicida glifosato. C. sumatrensis presento mayor tolerancia al herbicida que C. bonariensis. Ambas especies mostraron diferencias en la respuesta a glifosato en los dos estados de crecimiento evaluados, aumentando la tolerancia en el estado de elongacion de tallo.

Conyza sumatrensis y Conyza bonariensis son dos de las malezas más problemáticas en Argentina. En el sudeste bonaerense no existe información referida a la sensibilidad a glifosato de estas especies. Los objetivos de este trabajo fueron: a) determinar diferencias en sensibilidad a glifosato de C. bonariensis y C. sumatrensis, b) evaluar el efecto del estadio de crecimiento de plantas de C. bonariensis y C. sumatrensis sobre la eficacia de glifosato, y c) determinar la dosis letal media de glifosato para ambas especies. Se realizó un ensayo con plantas en estadio de roseta y elongación del tallo. En cada estadio se aplicaron dosis crecientes del herbicida glifosato (0, -1 0.5, 1, 2, 4, 8 y 12 L ha de producto formulado equivalente a 0, 180, 360, 720, 1080, 2880 y 4320 gramos de equivalente acido -1 (e.a) ha (CREDIT 48% sal; 36 g e.a). Se efectuaron evaluaciones visuales de control y se determinó la biomasa aérea. Se construyeron curvas de dosis respuesta ajustadas utilizando un modelo loglogístico y uno lineal plateau. Además, se calculó la dosis requerida para alcanzar el 50% de control (EC ). C.sumatrensis 50 mostró menor sensibilidad a glifosato que C. bonariensis. A mayor estadio de crecimiento se necesitó una mayor dosis de glifosato para lograr un mismo nivel de control. En estadio de roseta, la EC fue de 50 1.37 y 1.12 L ha-1 para C. sumatrensis y C. bonariensis, respectivamente. En estado de elongación ambas especies presentaron -1 mayores valores de EC (8.04 y 2.44 Lha , 50 respectivamente).

Conyza sumatrensis and Conyza bonariensis are two of the most problematic weeds in Argent ina. In the southeast of Buenos Aires there is no information regarding the sensitivity of Conyza species to glyphosate. The objectives of this work were: a) to determine differences in sensitivity of C. bonariensis and C. sumatrensis to glyphosate, b) to evaluate the effect of the growth stage of C. bonariensis and C. sumatrensis plants on glyphosate efficacy, and c) to determine the median lethal glyphosate dose for both species. An experiment was conducted with plants at the rosette and stem elongation stages. Increasing doses of glyphosate (0, 0.5, 1, 2, 4, 8 and 12 L ha(-1) of formulated product corresponding to 0, 180, 360, 720, 1080, 2880 y 4320 g acid equivalent ha(-1)) ( CREDIT 48% salt: 36g acid equivalent) were applied at each stage. Control was assessed visually, and aboveground biomass was determined. Dose-response curves were adjusted using the log-logistic and linear plateau models and the glyphosate dose required for 50% weed control (EC50) was calculated. C. sumatrensis was less sensitive to glyphosate than C. bonariensis. Later growth stages required a higher dose of glyphosate to achieve the same level of control. The EC50 values were 1.37 and 1.12 L ha(-1) for C. sumatrensis and C. bonariensis respectively in rosette stage, while in the stem elongation stage both species had high EC50 values (8.04 and 2.44L ha(-1), respectively).

Conyza sumatrensisis one of the most problematic weeds in Argentina because of its high seed production, rapid germination and a high dispersal ability of the seeds. In the last years, its presence has increased in all areas under no tillage. Although it is a very prolific species, intraspecific competence may affect its behavior. The objective of this work was to evaluate the pattern of emergence of C. sumatrensis and the intraspecific competition as a self-regulation process. Trials were conducted at the Agricultural Experimental Station of Balcarce, INTA, Argentina. Weed emergency was recorded monthly. Competitive ability was assessed by the response of growth and fecundity to densities ranging between 0 to 600 plants re. Emergence of C. sumatrensis was concentrated during the autumn (60 %) while a second peak was observed in the spring (20 %). The increase in plant density caused a decrease in height, number of branches and biomass (underground, aerial, and reproductive), as well as in seed production per plant. Growth and fecundity decreased until density reached 75 plants m(-2), above it they remained relatively constant. Results indicated a regulating effect on C. sumatrensis population that could restrict the reproductive potential of this species, and would also allow to estimate the optimal conditions to obtain certain sizes of plants and to evaluate the population responses to the application of the chemical treatments.

Imazamox, an herbicide belonging to the Imidazolinone chemical group, is registered in Argentina for soybean and for Clearfield (CL) wheat and sunflower. Due to its soil residual activity, it is important to study its phytotoxic persistence on sensitive crops. For this reason, the objective of this work was to determine the residual effects of two doses of Imazamox on winter and summer crops in Balcarce, in the southeast of Buenos Aires province, Argentina. Treatments consisted in the application of Imazamox to CL sunflower at 50 and 100 g of active ingredient/ha, and a control. After harvesting, soil samples were taken at monthly intervals (104, 138, 168, 207, 235, 266 and 298 days from application). At the end of sampling, a bioassay was carried out in a growth chamber with wheat, rape, sunflower and maize not tolerant to Imidazolinones. Field experiments were conducted with non-CL maize and sunflower and with two varieties of potato (Kennebec and Innovator) sown on the plots previously treated with Imazamox. The bioassay determined that length of persistence periods was as follows: rape > wheat = sunflower = maize. None of the field crops showed negative effects at the Imazamox doses applied, indicating that there was no residual effect.

Imazapyr is a broad-spectrum herbicide that belongs to the imidazolinone chemical family. In Argentina it is used on Imidazolinone-tolerant corn and sunflower Clearfield (R). Due to its low adsorption capacity, and high desorption capacity and soil persistence, imazapyr is prone to leaching into groundwater. There is a lack of information available regarding groundwater leaching of imazapyr in Argentina. Therefore, the objective of this study was to determine the risk of imazapyr leaching in three Argentinean soils (Tandil, Anguil and Cerro Azul sites). The indexes applied to estimate lixiviation risk of the herbicide imazapyr were GUS (Groundwater Ubiquity Score), RF (Retardation Factor) and AFT (Attenuation Factor log-transformed). The indexes were calculated using environmental properties (half-life and adsorption) obtained from batch experiments, and from pesticides databases. AFT was calculated for three rates of net groundwater recharges: 0.3, 1.1 and 2.3 mm day(-1). According to the GUS and AFT indexes, imazapyr has a high leaching potential, following the order Tandil > Cerro Azul > Anguil soils. The results indicate that the weak adsorption and high persistence of imazapyr may increase its movement in the soil profile and the risk of groundwater pollution.

Imazamox es un herbicida perteneciente a la familia de las Imidazolinonas que actualmente esta registrado en Argentina en soja, asi como en trigo y girasol Clearfield (CL). Debido a que posee accion residual en el suelo, es importante determinar su persistencia a fin de evaluar la factibilidad de siembra de cultivos sensibles a sus residuos. Por tal motivo, el objetivo de este trabajo fue determinar los efectos residuales de dos dosis de Imazamox sobre cultivos de invierno y de verano en la localidad de Balcarce, ubicada en el sudeste de la provincia de Buenos Aires, Argentina. Los tratamientos consistieron en la aplicacion de Imazamox en un cultivo de girasol CL en dosis de 50 y 100 g i.a/ha, incluyendose un testigo sin tratar. Luego de la cosecha del girasol, se realizaron siete muestreos de suelo a intervalos mensuales (104, 138, 168, 207, 235, 266 y 298 dias desde la aplicacion, DDA). Finalizados los mismos, se realizo un bioensayo con trigo, colza, girasol y maiz no tolerantes a imidazolinonas, en camara de crecimiento. A campo, se sembraron maiz y girasol no CL y papa de las variedades Kennebec e Innovator sobre los tratamientos previos de Imazamox, determinandose el rendimiento. Como resultado del bioensayo, se determino el siguiente orden de la longitud de los periodo de persistencia: colza>trigo=girasol=maiz. Ninguno de cultivos a campo mostro efectos negativos a las dosis aplicadas de Imazamox, indicando que no existio efecto residual sobre ellos.

In Argentina, glyphosate use has increased exponentially in recent years as a result of the widespread adoption of no‐till management combined with genetically modified glyphosate‐resistant crops. This massive use of glyphosate has created concern about its potential environmental impact. Sorption–desorption of glyphosate was studied in 3 Argentinean soils with contrasting characteristics. Glyphosate sorption isotherms were modeled using the Freundlich equation to estimate the sorption coefficient (Kf). Glyphosate sorption was high, and the Kf varied from 115.6 to 1612 mg1–1/nL1/n/kg. Cerro Azul soil had the highest glyphosate sorption capacity as a result of a combination of factors such as higher clay content, cation exchange capacity, total iron, and aluminum oxides, and lower available phosphorus and pH. Desorption isotherms were also modeled using the Freundlich equation. In general, desorption was very low (<12%). The low values of hysteresis coefficient confirm that glyphosate strongly sorbs to the soils and that it is almost an irreversible process. Anguil soil had a significantly higher desorption coefficient (Kfd) than the other soils, associated with its lower clay content and higher pH and phosphorus. Glyphosate high sorption and low desorption to the studied soils may prevent groundwater contamination. However, it may also affect its bioavailability, increasing its persistence and favoring its accumulation in the environment. The results of the present study contribute to the knowledge and characterization of glyphosate retention in different soils. Environ Toxicol Chem 2017;36:2587–2592. © 2017 SETAC

Conyza sumatrensis es una de las malezas más problemáticas en Argentina debido a su alta producción de semillas, rápida germinación y gran dispersión. En los últimos años, su presencia se incrementó en todas las áreas donde se realiza la producción de cultivos bajo siembra directa. Si bien es una especie muy prolífica, bajo condiciones de competencia intraespecífica puede afectarse su comportamiento. El objetivo de este trabajo fue evaluar la dinámica de emergencia de C. sumatrensis y la competencia intraespecífica como proceso de autoregulación poblacional. Los ensayos se realizaron en la Estación Experimental Agropecuaria de Balcarce, INTA Argentina. La emergencia de plántulas se registró mensualmente. Los efectos de la competencia intraespecífica se evaluaron a partir de las respuestas en crecimiento y fecundidad frente a densidades entre 0 y 600 plantas m-2. La emergencia de C. sumatrensis se concentró durante el otoño (60 %), observándose un segundo pico (20 %) en primavera. El incremento de la densidad de plantas provocó una disminución en la altura, número de ramificaciones y biomasa (radicular, aérea y reproductiva), así como en la producción de semillas por planta. El crecimiento y la fecundidad se redujeron hasta una densidad de 75 plantas m-2, por encima de la cual permanecieron relativamente constantes. Los resultados obtenidos demostraron que existió un proceso de regulación poblacional que podría restringir el potencial reproductivo de la especie, y permitirían además estimar las condiciones óptimas para obtener determinados tamaños de plantas y evaluar las respuestas poblacionales a la aplicación de los tratamientos químicos.

Imazapir es un herbicida de amplio espectro de control de malezas, perteneciente al grupo químico de las Imidazolinonas. En Argentina se aplica a gran escala en los cultivos de girasol y maíz Clearfield®. Debido a que posee baja capacidad de adsorción, alta capacidad de desorción y prolongada persistencia en el suelo, representa alto riesgo de lixiviación y de contaminación del agua subterránea. En Argentina es escasa la información generada al respecto. Por lo tanto, el objetivo de este trabajo fue determinar el riesgo de lixiviación del herbicida imazapir hacia el agua subterránea en tres suelos contrastantes del país (Tandil, Anguil y Cerro Azul). Se utilizaron los índices GUS (Groundwater Ubiquity Score), Factor de Retardo (RF) y Factor de Atenuación log-transformado (AFT), considerándose para el cálculo de este último tres recargas netas de agua subterránea: 0,3; 1,1; y 2,3 mm día-1. Los índices fueron estimados empleando las propiedades ambientales (vida media y adsorción) de bases de datos y obtenidas experimentalmente para cada sitio de estudio. De acuerdo a los índices GUS y AFT, imazapir presentó alto riesgo de lixiviación hacia el agua subterránea en los tres suelos, según el orden Tandil > Cerro Azul > Anguil. Los resultados mostraron que una débil adsorción y una elevada persistencia podrían conducir a una alta movilidad de imazapir en el perfil del suelo, lo cual implicaría un alto riesgo de contaminación del agua subterránea.

Variations in soil properties with depth strongly influence the degradation and persistence of herbicides, underlining the importance of studying these processes in soil horizons with distinctively different properties. The persistence of the herbicides acetochlor, atrazine, and S-metolachlor was measured in samples of the A, B, and C horizons of 2 Typic Argiudolls from Argentina under no-till management. The soils studied differed in soil organic carbon (OC) content, pH, particle size distribution, and structure. Quantification of herbicides in soil was done through high-performance liquid chromatography with diode array detector. There were interactions of herbicidexhorizon (p < 0.01) that resulted in degradation rates (k) of all herbicides decreasing, and their corresponding dissipation half-life (DT50) values increasing, with soil depth. Herbicide persistence across all soils and horizons ranged from 15 to 73 d for acetochlor, 13 to 29 d for atrazine, and 82 to 141 d for S-metolachlor, which had significantly (p < 0.01) greater persistence than atrazine and acetochlor. The DT50 values of herbicides were negatively correlated with the contents of OC (correlation coefficients ranging from -0.496 to -0.773), phosphorus (-0.427 to -0.564), and nitrogen-nitrate (-0.507 to -0.662), and with microbial activity (-0.454 to -0.687) and the adsorption coefficient (-0.530 to -0.595); DT50s were positively correlated with pH (0.366 to 0.648). Adsorption was likely the most influential process in determining persistence of these herbicides in surface and subsurface horizons. The present study can potentially improve the prediction of the fate of acetochlor, atrazine, and S-metolachlor in soils because it includes much needed information on the degradation of the herbicides in subsurface horizons. Environ Toxicol Chem 2017;36:3065-3073. (c) 2017 SETAC

Glyphosate is the most used herbicide in Argentina, accounting for 62% of the commercialized pesticides on the market. It is used as a weed controller in no-till systems, and it is also applied to various genetically modified crops (e.g., soybean, corn, and cotton). Although it has a high solubility in water, it tends to adsorb and accumulate in agricultural soils. The main objectives of this work were to compare the dissipation of glyphosate and the accumulation of its metabolite aminomethylphosphonic acid (AMPA) over time in three soils from agricultural areas of Argentina under long-term management with no-till (NT) and conventional tillage (CT) practices. There were no differences in dissipation between NT and CT, indicating that the glyphosate-degrading microflora was not modified by the different tillage managements. Moreover, tillage practices did not alter the general soil properties; therefore, glyphosate bioavailability was not affected by NT or CT practice. Forty percent of the applied glyphosate was degraded within the first three days in all soils, indicating a fast initial dissipation rate. However, the dissipation rate considerably decreased over time, and the degradation kinetics followed a bi-exponential (or two-compartment) kinetic model. No differences were found between tillage practices. Dissipation was not related to the microbial activity measured as soil respiration. The fast decrease in the concentration of glyphosate at the beginning of the dissipation study was not reflected in an increase in the concentration of AMPA. The estimated half-lives for glyphosate ranged between 9 and 38 d. However, glyphosate bioavailability decreases over time, as it is strongly adsorbed to the soil matrix. This increases its residence time, which may lead to its accumulation in agricultural soils.

The behavior of organochlorine pesticides (OCPs), such as DDTs, endosulfans, HCHs, heptachlors, drins and chlordanes, has been evaluated in the Quequén Grande River agricultural watershed including different matrices. Soil profiles from fields dedicated to soybean cultures and the associated terrestrial biota (earthworms, coleopteran larvae, collembolan and mites), stream water, suspended particle matter and surface sediment were sampled during the pre-application pesticide period. Pesticide analyses were carried out using gas chromatography with an electron capture detector. Soils samples showed a differential pesticide pattern throughout the profile. Control soils, settled 200 m from agricultural plots showed similar pesticide levels but with higher variety of compounds, denoting the historical use of OCPs in the zone. However, in agricultural plots DDTs and endosulfans constituted 90 % of the pesticides found with a further enrichment of endosulfan sulfate at depth. The relatively high p,p′-DDT levels in surface agricultural soil would be a consequence of pesticide impurities in technical acaricide Dicofol, which is widely used in the region; and it represents a new threat of fresh p,p′-DDT input into environment despite its use being forbidden. Terrestrial biota, mainly mesofauna showed high capacity to OCP accumulation, the aforementioned organisms being a good option in the monitoring of trace pesticides. Furthermore, the high OCP levels found constitute a hazard to food web since these organisms are one of the first steps in the food chain and the biomagnification is a common process with these compounds. As a result of runoff and volatilization the occurrence of OCPs in the aquatic environment was observed, draining a load of around 7.3 kg of pesticides into the river annually. As a whole, these results suggest the importance of using terrestrial biota for studying recalcitrant pesticides and a continuous monitoring is strongly advised as a first step in minimizing environmental risks.