The basin of El Cardalito stream (102.6 km2) is located in the southeast of Buenos Aires province (Argentina), near the city of Mar del Plata. An important horticultural belt with intensive use of agrochemicals is located in it. The objective of this work was to estimate the potential risk of leaching of the most commonly used herbicides, insecticides and fungicides in the basin. For this purpose, we used the Retardation Factor (RF) and the Attenuation Factor log transformed (AFT) indexes. Both RF and AFT were calculated for the A, B and C horizons of the five soil series that integrate the watershed, as well as for the complete soil profile, taking into account their properties and depth. According to the RF, the leaching potential of the pesticides was higher in the C horizon, compared to A and B horizons or the complete profile. In the C horizon, the insecticides with higher mobility were Carbofuran, Methamidophos, Pirimicarb, Imidacloprid and Thiamethoxam. In the case of fungicides, the highest mobility was found in Fosetyl-aluminium, Captan, Zineb and Carbendazim. On the other hand, 12 of the 25 studied herbicides had high mobility, particularly Dicamba, Picloram and Naptalam. The AFT values indicated that for most of the pesticides, the risk of leaching was higher in the C horizon, followed by A and B horizons. In all cases, the risk of leaching increased with water recharge, reaching its maximum at 2.3 mm day-1. Finally, considering the soil profile, leaching of most pesticides evaluated, except Picloram, would range between unlikely and very unlikely for all the studied recharges (0.3, 1.1 y 2.3 mm day-1). The indices used are valuable tools for estimating the vulnerability of aquifers due to leaching of pesticides, however it is essential to perform field monitoring to verify the degree of association with reality.

La cuenca del arroyo El Cardalito (102.6 km2) se encuentra localizada en el sudeste de la provincia de Buenos Aires (Argentina) cerca de la ciudad de Mar del Plata, donde existe un importante cinturón hortícola con uso intensivo de agroquímicos. El objetivo del trabajo consistió en estimar el riesgo potencial de lixiviación de los herbicidas, insecticidas y fungicidas comúnmente utilizados en dicha cuenca. A tal fin, se utilizaron los índices conocidos como factor de retardo (RF) y factor de atenuación log-transformado (AFT). Tanto el RF como el AFT se calcularon para los horizontes A, B y C de las cinco series de suelo que integran esta cuenca, así como para el perfil completo, teniendo en cuenta sus propiedades y profundidad. Considerando el RF, la capacidad de lixiviar de los plaguicidas fue superior en el horizonte C de los suelos respecto de los horizontes A y B o el perfil. En ese horizonte, los insecticidas con mayor movilidad fueron carbofuran, pirimicarb, metamidofós, imidacloprid y tiametoxam mientras que en el caso de los fungicidas fueron fosetil aluminio, Captan, zineb y carbendazim. Por su parte, se estimó que 12 de 25 herbicidas considerados presentaron elevada movilidad, especialmente dicamba, picloram y naptalam. En el caso del AFT, se determinó, para la mayoría de los plaguicidas, que la capacidad de lixiviar varió según el horizonte considerado de acuerdo al orden C > A > B, mientras que para todos los horizontes la peligrosidad se incrementó al aumentar la recarga neta, siendo máxima a 2.3 mm día-1. Por último, considerando el perfil de suelo, se determinó que la lixiviación de la mayoría de los plaguicidas evaluados, a excepción de Picloram, sería improbable a muy improbable para las recargas estudiadas (0.3, 1.1 y 2.3 mm día-1). Si bien los índices utilizados constituyen valiosas herramientas para estimar la vulnerabilidad de los acuíferos por lixiviación de plaguicidas, resulta imprescindible la realización de monitoreos a campo que verifiquen el grado de asociación con la realidad.

The determination of adsorption and dissipation parameters of pesticides in soils allows for better prediction of their behavior and potential for groundwater contamination. The objective of this study was to compare two methods of estimating the indices for retardation factor and for attenuation factor logtransformed (AFT). The indices were applied to estimate lixiviation risks of the herbicides acetochlor, atrazine and s-metolachlor in the horizons A, B, C and the whole profile for two soils from Buenos Aires province (Argentina). The comparison of the methods consisted in estimating the indices using adsorption and persistence of herbicides obtained from batch experiments (multilayer setting) and from databases (monolayer setting). Herbicide sorption (Koc) and half-life (T1/2) were determined for horizons A, B and C from controlled batch experiments. Estimates of AFT calculated from batch experiments for different recharge rates (0.3, 1.1 and 2.3 mm/day), resulted in very unlikely leaching potentials for the three herbicides in all horizons and soil profiles. However, using tabulated indices it was determined an increased leaching risk, which increased with increasing depth in the following order C> B> A> profile.

La determinación de los parámetros de adsorción y disipación de plaguicidas en el suelo permite un mejor pronóstico de los procesos y del potencial de contaminación del agua subterránea. El objetivo fue comparar dos métodos de cálculo de los índices factor de retardo y de atenuación log-transformado (AFT), a fin de estimar el riesgo de lixiviación potencial de los herbicidas atrazina, acetoclor y s-metolacloro en los horizontes A, B, C y en todo el perfil de dos suelos de la provincia de Buenos Aires (Argentina). Se elaboraron los índices a partir de los parámetros de adsorción y persistencia de los herbicidas obtenidos mediante experimentos con enfoque multicapa, respecto de cálculos mediante bases de datos con enfoque monocapa. Se determinó el índice de adsorción y el tiempo de vida media para los tres horizontes, a partir de experimentos bajo condiciones controladas. De acuerdo al AFT, calculado para diferentes recargas (0,3; 1,1 y 2,3 mm/día) mediante información de los experimentos multicapa, se estimó un potencial de lixiviación muy improbable de los tres herbicidas en todos los horizontes y perfiles. La utilización de índices tabulados determinó un mayor riesgo de lixiviación, que tendió a incrementarse a mayor profundidad según el orden C>B>A>perfil.

O objetivo do presente trabalho foi estudar a persistência da atrazine em solos do sudoeste da Província de Buenos Aires, Argentina, por meio de bioensaio com aveia. Estudaram-se doses de atrazine de 0; 0,58; 1,16 e 2,32 mg.g-1 de solo seco (SS), os quais foram aplicados em vasos que continham solos de Balcarce, A. Gonzáles Chaves e San Cayetano. O conteúdo de matéria orgânica (MO) dos solos foram 5,70; 5,15 e 3,84% para Balcarce, A. Gonzáles Chaves e San Cayetano, respectivamente. Avena sativa cv. Millauquén foi semeada em vasos e cultivada sob condições de casa-de-vegetação até o desenvolvimento completo da segunda folha. A porção aérea das plantas foi colhida e determinado o peso da matéria seca. Com os dados obtidos calculou-se o peso relativo da matéria seca (PRMS), com relação ao tratamento sem herbicida. Após um período de tempo curto de descanso, repetiu-se o processo anterior, até totalizar quatro períodos sucessivos. A fitotoxicidade da atrazine foi expressa em termos de 50% de redução do PSR (GR50), nos solos avaliados. Aos 42 dias da aplicação obtiveram valores de GR50 de 0,30; 0,64 e 0,90 mg.g-1 SS nos solos de San Cayetano, balcarce e A.G. Chaves, respectivamente. A persistência de atrazine na dose recomendada (1,16 mg.g-1), considerando uma redução de 80% do PSR, foi de 100, 143 e 221 dias desde a aplicação para A.G. Chaves, Balcarce e San Cayetano, respectivamente. Estes resultados são consistentes com o menor conteúdo de MO e capacidade de troca catiônico, assim como o maior pH para o solo de San Cayetano, com relação aos solos restantes estudados.

Atrazine persistence in soils of the southeast of Buenos Aires Province, was studied by an oat bioassay. Atrazine doses of 0.58, 1.16, and 2.32 mg.g-1 dry soil weight (DSW) were applied to pots containing soils from Balcaree, A. Gonzáles Chaves and San Cayetano sites, whose organic matter (OM) content of soils were 5.70, 5.15, and 3,84%, respectively. Avena sativa cv. Millauquén plants were grownth in the pots under greenhouse conditions at different times after atrazine application. Shoots were evenly cut above the soil and dry weight determined as a measure of plant growth. Plants grown in non-sprayed soil were used as controls. Relative dry weight (RDW) of shoots was calculated as percentage of control. Atrazine phytotoxicity was expressed in terms of 50 % plant growth reduction (GR50) in the soils under study. Herbicide persistence was expressed in terms of days after treatment (DAT) needed for the plant to achieve 80% of RDW. Atrazine GR50 values of 0.30, 0.64, and 0.90 mg.g-1 DSW in soils from San Cayetano, Balcare and A.G. Chaves, were respectively obtained at 42 DAT. Herbicide persistences at the recommended dose (1.16 mg.g-1) were 100, 143, and 221 DAT for A.G. Chaves, Balcarce and San Cayetano soils, respectively. San Cayetano soil had both the lowest OM content and cation exchange capacity (CEC), as well as the highest pH, of all the soil studied here. These results were consistent with both the lowest GR50 and the highest persistence abtained for atrazine in this soil.