Evaluation of the fate and transport of veterinary antibiotics in the environment is currently hampered by the limited understanding of antibiotic sorption mechanisms onto environmental solids. In this study, the sorption interactions of tetracycline, fluoroquinolone and sulfonamide antibiotics to whole soils and manure were investigated. Results showed that antibiotics from tetracycline and fluoroquinolone classes sorb to whole soils primarily through cation exchange, surface complexation and cation bridging. Similar sorption behavior among compounds from each class was observed, suggesting that future experiments need only investigate a representative compound from which the sorption behavior of other compounds in the same class may be inferred. Sulfonamide compounds were an exception in that significant variation in sorption behavior was seen among compounds from this class. A critical review of literature regarding antibiotic sorption to organic matter showed that most antibiotic compounds sorb through cation exchange with secondary mechanisms being cation bridging and hydrogen bonding. Further studies are needed to evaluate whether the acidity of organic matter is a better normalizing parameter than the amount of organic carbon for comparing sorption among antibiotic compounds. The relative importance of hydrogen bonding as a sorption mechanism must also be explored. Investigation of antibiotic sorption to manure showed that antibiotics tend to be dissolved in aqueous solution even in the presence of suspended manure particles. Manure solids sorbed tetracycline and fluoroquinolone compounds significantly while less sorption was observed for sulfonamide.
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