In a recent literature survey published by Samsel and Seneff, an argument is made for a possible link between the incidence of celiac disease in the United States and the use of the herbicide glyphosate. A key element of the authors’ argument is based on a single example of a study with fish (Senapati et al., 2009). In that study, adverse effects were observed in fish that were exposed to water containing a glyphosate-based herbicide. Samsel and Seneff concluded that the effects observed in the fish were "highly reminiscent of celiac disease." The Senapati fish paper is itself deeply flawed, but it is also irrelevant.
Senapati et al. exposed fish in tanks to a glyphosate rate of 4mg/L, added as a commercial formulation manufactured in India, called Excel Mera-71. That is a formulation made for terrestrial, not aquatic, use, and it is described as containing glyphosate and "a blend of non-ionic and cationic surfactants." At least in the United States, products registered for use on emerged weeds growing in water do not contain surfactants, because they are known to injure fish. The 4mg/L concentration used in the Senapati study was also more than twice as high as the highest rate allowed for a legitimate aquatic formulation, AquaMaster, in the United States. In addition, the water in which the fish were kept was replaced every other day for 45 days with a fresh supply of the surfactant-containing herbicide—not something relevant to any real-world situation. There was no surfactant control in this study, even though surfactants are well known for being able to cause injury to the gills and digestive tracks of fish. The Senapati study simply redocumented the fact that long-term, high-rate exposure of fish to surfactants is damaging, while glyphosate and its primary metabolite, AMPA, are classified as "practically non-toxic" to fish by the EPA.
There is no pattern of potential glyphosate exposure for humans in the United States that is even remotely like that in this poorly designed fish study. The formulation surfactants would not be present in human foods, the rates of glyphosate would be orders of magnitude lower and they would be in the form of the metabolite AMPA.
The Senapati study simply provides no meaningful data that Samsel and Seneff can use to connect glyphosate and celiac incidence.