Presentation of multistep isotherms formed at the adsorption of herbicides

Abstract

The soil as an adsorbent has various active sites leading to rather complicated adsorption mechanisms with environmental pollutants, like pesticides. According to earlier results the chloroacetanilide type herbicides as solutes resulted in two-step isotherms on soils and quartz. This phenomenon has not been observed yet concerning trace compounds in the environment. In this case the so-called distributed reactivity model is used, suggesting that the total sorption is given as the sum of the local adsorption isotherms. The adsorption of isoproturon (urea-type herbicide) and prometryn (s-triazine type herbicide) was studied on quartz at different pH values, leading to similar – multistep – isotherms generated by chloroacetanilide compounds. These plots were compared to the classification suggested by Giles. If the formation of different associates is supposed the following adsorption equation can be derived. Its applicability is proved by the fitting of the isotherms of herbicides having different structures. This isotherm equation can be used widely for environmental as well as for (other) colloidal systems.

Acknowledgement This research was funded by the Hungarian research program KAC (no. K0440802001).