Die adsorpsie van atrasien deur verskillende kleiminerale en die invloed daarvan op die mobiliteit van atrasien

Abstract

Atrazine (2-chloro-4-ethylamino-6-isopropylamino-1,3,5-triazine)is a pre-emergence herbicide used mainly on maize. The influence of various clay minerals, i.e. illite-vermiculite mixtures, montmorillonite, kaolinite, goethite and hematite on the adsorption of atrazine under different conditions (pH, temperature, different saturation cations and electrolyte concentration) was investigated. The adsorption energy of atrazine was determined and from this it was concluded that the mechanism, of adsorption may be described as physical. Adsorption isotherms of atrazine conforms to the Freundlich equations. It was also concluded that, although atrazine is adsorbed by some clay minerals under specific conditions in laboratories, the role of clay minerals and clay content in the immobilization of atrazine under natural conditions are over-emphasized. This results in the application of excessive quantities of atrazine for the control of weeds in maize fields, which enhances the contamination of groundwater and water in reservoirs. Only sodium and potassium saturated montmorillonite and a low pH influenced the adsorption of atrazine substantially. The movement of atrazine under controlled conditions was investigated with the aid of a rain simulator. Two different soils were used i.e. avalon and vertisol. Most of the applied atrazine remained in the soil during the period of investigation. Artrazine was distributed throughout the avalon profile but was restricted to the upper 50 mm in the vertisol profile. Soil water and water from a pan in the Viljoenskroon area were monitored. Atrazine was detected in soil water as well as water of the pan. The concentration of atrazine in the water varied according to the seasons and correlates with monthly rainfall. Transference of atrazine between seasons occurred in both the groundwater and water of the pan but not in the reservoirs. This information confirms that movement of atrazine to water reservoirs may take place. Different dams (Vaal, Loskop, Koppies, Wentzel and Strydom dam) and Zuikerbosch Pump Station were monitored for the presence of atrazine. Atrazine was detected in all the dams. The concentration correlates with variables such as calcium, sodium, potassium and chlorine and showed a seasonal tendency. From this study it was concluded that atrazine contaminates groundwater and water in reservoirs. Concentration of atrazine in drinking water exceeded the limits prescribed by the World Health Organization. The possible presence of hazardous quantities of atrazine in groundwater and water of dams needs urgent attention.