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Temperature Dependence of Linuron Sorption to Three Different Agricultural Soils

Swedish University of Agricultural Sciences, Div. Water Quality Research, P.O. Box 7072, S-75007 Uppsala, Sweden.

^* Corresponding author (jorg.brucher{at}mv.slu.se).

ABSTRACT

The temperature dependence of sorption of the herbicide linuron (N'-(3,4-dichlorophenyl)-N-methoxy-N-methylurea) was investigated in three texturally different soils (two sandy soils and one clay soil), each of which had been divided into three layers (0–30, 30–60, and 60–90 cm). Four different temperatures were used, ranging from 277 to 296 K (4–23°C). The sorption tests were conducted according to the Organization for Economic Cooperation and Development (OECD) standard batch-equilibrium method, in which sieved soil was gently shaken with aqueous linuron solution for 16 to 25 h. In most cases, the sorption isotherms obtained could be described satisfactorily with the Freundlich sorption function. Analyses based on the derived isotherms and calculated K_d values revealed some general patterns: (i) sorption changed significantly (K_d values changed by a factor up to 15 at low linuron concentrations) over the investigated temperature range in all soils; (ii) the nonlinearity of the isotherms increased with decreasing temperature in the sandy soils, but decreased in the clay soil; and (iii) the temperature dependence of sorption was generally stronger at lower linuron concentrations. Based on the sorption data, the free energy and heat of sorption were calculated. These results were then used to describe sorption at any temperature and concentration within the ranges investigated.