HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Spurlock, F. C. Search for Related Content PubMed Articles by Spurlock, F. C. Agricola Articles by Spurlock, F. C.

Estimation of Humic-Based Sorption Enthalpies from Nonlinear Isotherm Temperature Dependence: Theoretical Development and Application to Substituted Phenylureas

Hydrologic Sciences, Department of Land, Air and Water Resources, University of California, Davis, CA 95616.

^* Corresponding author.

ABSTRACT

Thermodynamic assessments of organic chemical-soil interactions are important for understanding various aspects of sorption phenomena, including isotherm nonlinearity. Expressions were derived here for calculating organic carbon based Freundlich nonlinear sorbed phase partial molar enthalpies (₁) and entropies (₁) from isotherm temperature dependence. It was shown that, in general, any changes in nonlinearity with temperature must be evaluated when estimating enthalpy effects from isotherm temperature dependence. The results were applied to nonlinear soil sorption data of three substituted phenylurea herbicides between 281 K and 297 K. The ₁ estimated at 289 K were found to range down to approximately –50 kJ mol^–1, and were associated with negative ₁. Differential heats of sorption, which also include solution phase interactions, were 10 to 15 kJ mol^–1 more exothermic than ₁. The ₁ were significantly less exothermic as sorbed phase concentrations increased. For diuron (1,1-dimethyl-3-(3,4-dichlorophenyl) urea), a compound that displays comparable solubility and octanol-water partition coefficient as naphthalene, ₁ at higher concentrations were similar to values estimated for naphthalene (approximately –4 to + 10 kJ mol^–1, calculated here from literature data), a nonpolar compound without polar functional groups. The data suggest that specific interactions between the phenylureas and soil organic matter moieties are dominant at low sorbed phase concentrations, but become less important relative to nonspecific London-van der Waals forces as sorbed phase concentration increases. The urea isotherms are therefore nonlinear, with nonlinearity fundamentally related to the nature of substituted phenylurea sorbed phase interactions.

This article has been cited by other articles:

				J. A. Field, R. L. Reed, T. E. Sawyer, S. M. Griffith, and P. J. Wigington Jr. Diuron Occurrence and Distribution in Soil and Surface and Ground Water Associated with Grass Seed Production J. Environ. Qual., January 1, 2003; 32(1): 171 - 179. [Abstract] [Full Text] [PDF]