Letter▼ Reviewers and authors must attend to details I am writing regarding a general concern about the content of ES&T research articles, using as an example a recent paper entitled, “Modeling the Kinetics of the Competitive Adsorption and Desorption of Glyphosate and Phosphate on Goethite and Gibbsite and in Soils” (Environ. Sci. Technol. 2004, 38, 1718–1722). This well-written paper describes work that appears to have been carefully done. Several questions that emerged when I read the paper prompted me to write to the authors to seek further details of their work, particularly their analytical procedures and the choice of the labeling site in the glyphosate molecule. Although the reply I received from the corresponding author supplied virtually all of the details that were, in my opinion, missing, the paper as published is only one of many examples of the way in which authors and reviewers in general treat analytical method details in research being published in ES&T. Analytical chemistry is an indispensable tool for environmental science and technology, and choices made in the course of well-conceived experiments need to be described to rule out ambiguities that could destroy the author’s conclusions. If the analytical details are glossed over or not mentioned at all, the paper’s value may be severely diminished. In the example paper, the authors set out to examine the sorption of the herbicide glyphosate to several representative Danish soils using C-14labeled glyphosate. To avoid the ready microbiological degradation of the herbicide in the soil slurries studied, the authors treated their samples with sodium azide. Analyses of filtrates were carried out by liquid scintillation counting. The global importance of the work is that glyphosate and phosphate (the soil nutrient
added as fertilizer) appear to sorb to the same sites in the soil, implying that saturation of sorption sites in the soil with one adsorbate (e.g., phosphate) could interfere with the sorptive soil inactivation of the herbicide. (Glyphosate, once in the soil, is normally assumed to be bound and thus rendered harmless.) Similarly, a zerotilled soil repeatedly treated with glyphosate might not be able to sorb phosphate or might release phosphate under some conditions, leading to nutrient enrichment of waterways. The paper’s authors examined the combination of sorptive phenomena in soils using models, which were based on laboratory experiments and analyses not fully described in the article. The reviewers appear not to have requested that the missing information be provided. For instance, the C-14-labeled carbon in the glyphosate is not identified. There are three different carbon atoms in the glyphosate molecule, and their fate following degradation of herbicide in the soil may be quite different. Thus, it is essential that this information be revealed. The corresponding author has advised me that the glyphosate was labeled at the carbon in the phosphonomethyl group and that the glyphosate did not degrade in the soil during the experiments. The missing details would have added confidence. The microbial action in the soil was controlled by adding sodium azide, thus preventing the formation of glyphosate metabolites that would have been indistinguishable from glyphosate by the method used. The azide-treated soil was not tested for biological activity, nor were any independent analyses done to show the absence of glyphosate metabolites (aminomethylphosphonic acid and sarcosine) in the soil slurry filtrates. Liquid scintillation counting is susceptible to quenching by dissolved humic matter in the soil water. Although I have been advised that the authors found the soil filtrate color-
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less, this could not be assumed, because many other soils contain sufficient soluble organic matter to interfere with liquid scintillation counting by quenching. Sterilizing soil for herbicide fate work is invariably fraught with uncertainties. Sodium azide can be an effective sterilant, but its effect on the chemistry of the whole soil cannot be dismissed. In addition, the authors did not examine the possible effect of the azide treatment on the sorption of either glyphosate or phosphate, and these shortcomings were not picked up by the reviewers, either. In fact, the authors believe by deduction that the soil was sterile and that there was no effect on sorption; however, they did not say so in the paper. Rather than focus further on this one paper, I believe that it would be more productive to make it known to authors and reviewers alike that details of analytical and related chemistry are essential components of papers in environmental science and technology. In these days when many analytical samples are sent off to contract laboratories rather than researchers performing or overseeing the work themselves (although the work in the cited paper here was not done this way), it is, I believe, particularly important that the analytical and related chemistry be carefully described so that the work’s full implications can be appreciated. Modeling work is very useful in predicting the behavior of environmental contaminants. However, the analytical chemistry underlying the testing of these models must be carried out—and be published as having been carried out—properly to ensure that the models are valid. Papers reporting such work are significantly stronger when this chemistry is well described. Sincerely, BARRIE WEBSTER SWSTI Technologies Inc. Winnipeg MB Canada R3T 0c8
[email protected] © 2004 American Chemical Society
