Role of organic matter, clay, and iron contents in the sorption of oxytetracycline on river sediments

Background: Oxytetracycline (OTC) is a widely-used antibiotic; metabolism studies indicate only partial assimilation of it inside the body. Traditional wastewater treatment plants cannot remove OTC, and this results in the release of considerable amounts of the drug into aquatic environments. There is much concern over the role of residual antibiotics in the development of new generations of bacteria with modified resistance to the antibiotics. The present work investigated the possibility of OTC sorption on river sediments. Methods: Seven sediment samples were collected from various locations and depths of the Passaic River in New Jersey. The texture, clay, extractable iron, and organic matter contents of the sediments were determined. Pyrolysis-gas chromatography-mass spectrometric (Py GC-MS) analysis indicated the presence of 3 categories of organic materials: petroleum hydrocarbons, anthropogenic, and plant residual materials. The sediment samples were equilibrated with OTC solutions for 24 hours followed by centrifugation and syringe filtration. The residual OTC contents were determined by high performance liquid chromatography. Results: It appeared that 35%-60% fractions of OTC were retained by the sediments. The sorption capacity values of the sediments were correlated with clay content, organic matter content, and available iron. A poor correlation was found between adsorption capacity and clay content in the presence of organic matter and iron. Meanwhile, a relatively strong correlation was found between adsorption capacity with the iron, R2 = 0.7499, and organic matter contents of the sediments, R2 = 0.7899. Thus, the sorption of OTC on sediments is governed by all constituents. Conclusion: It was concluded that the antibiotic-sediment interaction is controlled mainly by the organic matter and iron contents.