PASSAGE OF SAND PARTICLES THROUGH THE GASTROINTESTINAL TRACT OF DAIRY COWS R. G, Patzer, G. D. Potter, and W. W. Sutton National Environmental Research Center, Las Vegas* SUMMARY REPORT Dairy cattle ingest moderate amounts of soil particles during normal foraging. These particles are ingested after becoming deposited on forage plants by air currents, or because they are associated with plant roots ingested by cattle. In addition, soil that becomes deposited on the snouts of cattle is licked off and ingested. increasing frequency such soil contains toxic pollutants. With The gastro- intestinal absorption efficiency for a pollutant is related to the residence time of the material in the gut, and the residence time should vary for different sizes of particles which the animal may ingest. Transuranic elements are usually in almost insoluble chemical forms when found in environmental media. It has been shown, however, that relatively insoluble forms of plutonium, for example, are solubilized to a considerable degree in the gastrointestinal environment of cattle. Information on the gastrointestinal passage rates for various soil particle sizes is, therefore, relevant to the potential absorp- tion efficiency fer substances entrained in debris ingested by animals grazing in contaminated areas. This study was performed to elucidate the variability in bovine gastrointestinal passage rates following oral ingestion of sand particles of various sizes. *See footnote, p. Silica sand of four graded size ranges 35. 47