Comment on "Sorption of Organic Chemicals to Soil Organic Matter: Influence of Soil Variability and pH Dependence"

Authors: Sierra Rayne

In their article, Bronner and Goss [Environ. Sci. Technol., 2011, 45, 1307-1312] investigate the pH dependence of organic chemical sorption to soil organic matter. The authors report a log Koc value for benzoyl chloride in aqueous solution, despite this compound having a known hydrolysis half-life of only 16 seconds in water. This timeframe is far too short to allow the measurement of any equilibrium based partitioning coefficients. Consequently, one suspects that the log Koc value reported for benzoyl chloride is likely that of its hydrolysis product: benzoic acid. The authors also may have chosen two experimental conditions (pH 4.5 and 7.2) between which the ionization state of the carboxylic acids in the organic matter may have changed very little, and could instead have remained in effectively the same net ionization state between the two experimental pH endpoints. Thus, there does not appear to be sufficient evidence in this work to support the general claim therein that "protonation/deprotonation of carboxylic groups in humic matter has no significant influence on sorption ... even for polar organic molecules."

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[v1] 2013-04-03 21:56:39

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