Abstract
The increased use of veterinary antibiotics in modern agriculture for therapeutic uses and growth promotion has raised concern regarding the environmental impacts of antibiotic residues in soil and water. The mobility and transport of antibiotics in the environment depends on their sorption behavior, which is typically predicted by extrapolating from an experimentally determined soil-water distribution coefficient (Kd). Accurate determination of Kd values is important in order to better predict the environmental fate of antibiotics. In this paper, we examine different analytical approaches in assessing Kd of two major classes of veterinary antibiotics (sulfonamides and macrolides) and compare the existing literature data with experimental data obtained in our laboratory. While environmental parameters such as soil pH and organic matter content are the most significant factors that affect the sorption of antibiotics in soil, it is important to consider the concentrations used, the analytical method employed, and the transformations that can occur when determining Kd values. Application of solid phase extraction and liquid chromatography/mass spectrometry can facilitate accurate determination of Kd at environmentally relevant concentrations. Because the bioavailability of antibiotics in soil depends on their sorption behavior, it is important to examine current practices in assessing their mobility in soil.
Highlights
Veterinary pharmaceuticals (VPs) are physiologically active compounds that are used to protect animals against parasites, prevent bacterial infections, and growth promotion [1,2,3,4,5,6]
Because the sorption properties of antibiotics affect their mobility and ecotoxicology, it is important to recognize that different Soil-water partition coefficient (Kd) measurements may provide varying results that could potentially lead to large errors in environmental models that are used in risk assessment
The purpose of this paper is to provide a review of the different ways that Kd values are measured, and demonstrate how the analytical differences may affect the prediction of the fate and transport of antibiotics in the environment
Summary
Veterinary pharmaceuticals (VPs) are physiologically active compounds that are used to protect animals against parasites, prevent bacterial infections, and growth promotion [1,2,3,4,5,6]. The pH-dependence of antibiotic sorption is critical, because many pharmaceuticals have acid-base properties resulting in changes in the overall net charge of the molecule as ammonia concentration in manure changes [6] These factors can alter the distribution between the aqueous and solid phase, for ionizable compounds [23]. Effects of ionic strength on tylosin sorption Literature suggests that tylosin sorption decreases with increase in ionic strength due to the consequent change in pH, and as a result of competition between the electrolyte cations and the positively charged tylosin species for negatively charged sorbent [6]. Complications could arise from the presence of both dissolved and suspended OM within the solution This complexity can be observed in the change in Kf values with increasing tylosin concentration (Table 5). The conversion of the parent compound to metabolites and the interconversions that occur under varying conditions are challenges associated with analyzing degradation products
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