Interactions between herbicides and humics acids present in soils

J.S. RIVA; A.V. JUAREZ; L. M. YUDI

Herbicides properties, Crop protection and Environmental hazards

NOVA Science Publishers, INC

Lugar: New York; Año: 2011; p. 211 - 230

S-triazines (1,3,5 ? Triazines) are an important group of herbicides which are able to incorporate into weed and inhibit photosynthesis enzymes. The use of these herbicides requires knowledge of their stability and transformation in the environment as well as their influence on micro-organisms. Triazine herbicides are stable in the soil for severalmonths and they, as well as some of their degradation products, are used by water and soil microbes as a source of energy (alkyl fragments) and nitrogen (amine fragments). In the last years, the environmental pollution by pesticides has become in a serious problem especially in marine ecosystem. Due to their heavy use in agriculture and to their persistence, many of the compounds are present in surface and ground waters, and have to be considered a potential risk for marine life as well as for drinking water quality.Development of new sensitive and selective analytical techniques for the determination of s-triazine herbicides and their metabolites in the environment as well as the recognition of their interactions with different elements, especially with heavy metals cations or organic molecules, as humic acids, present in soils, are important problems in modern s-triazine chemistry, because they determine pesticide mobility, bioavailability and effectiveness. The most important physicochemical properties of these pesticides and their degradations products are the solubility in water and the capacity to be retained by the organic matter of the soil. Humic acids are widely distributed in soils and, under natural conditions, they have been found as colloid suspension in water forming a large part of the dissolved carbon. Organic pollutants, such as herbicides, can exist in dissolved state or in association with the colloidal phase, or adsorbed by the soil. The driving forces of this adsorption involve electrostatic interactions, hydrogen bond, charge transfer, acceptor ? donor mechanisms, Van der Waals forces and hydrophobic interactions. These mechanisms operate simultaneously and their competition determines the retention of herbicides in soil and aquatic systems and, in consequence, their adsorption, transport, degradation processes and the fate in the environment. In this chapter we present the results reported by us and others authors concerning with the study of interactions between humic acids and herbicides in general, and s-triazines in particular, giving special attention to electrochemical methods.