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Microbial mineralization of atrazine was characterized in soils and liquid media in the presence of nitrogen fertilizer concentrations representing typical field applications. The mineralization of atrazine in soils varied between 6 and 99% after 18 d of incubation. Half-lives of between 0.99 and more than 18 d were obtained. Mineralization kinetics and degree are related by a reciprocal trend to concentrations of available nitrogen in the soil. In liquid media, half-lives were calculated as 0.12 d in the absence of fertilizer nitrogen and as 79 d in the presence of 1,000 mg/L of KNO3-N. Only 20% of atrazine was mineralized after 18 d of incubation in the presence of this concentration of KNO3-N, whereas greater than 90% mineralization occurred after 2 d of incubation in liquid medium without KNO3-N. The results demonstrate that the mineralization of atrazine is inhibited even at fertilizer nitrogen levels lower than typical field applications. Inhibition in soil is lower than that in liquid medium, possibly because of the higher complexity of the soil system. This may explain why atrazine that infiltrates to the groundwater is persistent. The microbial consortium of the soils was characterized, and seven species were identified. The degrading capacity of these species suggests that only three species are involved in the degradation of atrazine.

Palabras clave: herbicida, disponibilidad, vida media RESUMEN La atrazina es ampliamente utilizada en México y el estado de Morelos en la eliminación de maleza de hoja ancha en cultivos de maíz, sorgo, caña de azúcar y piña. Su uso está prohibido en la Unión Europea y restringido en Estados Unidos de América. Hasta el momento sólo se han caracterizado los procesos que influyen en la migración de atrazina sin presencia de emulsificantes y surfactantes. El presente trabajo tiene como objetivo caracterizar la adsorción y la biodegradación de atrazina al 100 % y gesaprim (producto comercial con 43 % atrazina y mezclado con surfactantes y emulsificantes), en diferentes muestras de suelo agrícola del estado de Morelos. Se hicieron muestreos en tres municipios: Moyotepec, Yecapixtla, y Huautla, con base en las diferentes texturas del suelo (arenosos, limosos y arcillosos). Los suelos fueron caracterizados fisica y químicamente, asimismo se obtuvieron las cinéticas de biodegradación con atrazina al 100 % como ingrediente activo y con el producto comercial gesaprim que contiene 43 % de atrazina como ingrediente activo.. Las vidas medias en los suelos Moyotepec, Yecapixtla y Huautla para el gesaprim fueron 126, 18 y 40 d y los porcentajes de biodegradación de 21.4, 71.8 y 50.1 %. Para atrazina al 100 %, fueron de 17, 16 y 6 d y los porcentajes de degradación de 52.7, 72.9 y 65.8 %, respectivamente. Con base en las vidas medias de atrazina al 100 % y gesaprim (43 % atrazina), se observó que la presencia de surfactantes y humectantes disminuye la velocidad de biodegradación y el porcentaje de biodegradación, con lo que se favorecen otros procesos de disipación, debido probablemente a que aumenta la disponibilidad del herbicida.Key words: herbicide, availability, half-life ABSTRACT Atrazine is widely used in Mexico and in the state of Morelos to eliminate broadleaf weeds in maize, sorghum, sugarcane and pineapple crops. Its use is prohibited in the European Union and restricted in the United States of America. So far, only processes that influence atrazine migration without the presence of emulsifiers and surfactants have been characterized. The present work aims to characterize the adsorption and biodegradation of pure atrazine (100%) and gesaprim (commercial product with 43 % atrazine mixed with surfactants and emulsifiers), in different samples of agricultural Rev. Int.