Analysis by microscale affinity chromatography of humic acid interactions with pharmaceutical micropollutants

Growing concern over the presence of pharmaceuticals in both the environment and water has led to increased interest in the effects such substances may have on human and environmental health. One factor that may affect the bioavailability, transport, and persistence of these compounds is their binding to natural and dissolved organic matter in the environment. One example of this type of substance is humic acid, a complex biomaterial that is present in water and soil and that is formed through plant and animal decay. This report uses microscale affinity chromatography with supports made by non-covalent entrapment to examine and compare the binding of humic acid with several drugs that are found as contaminants in environmental water. Leonardite humic acid is used as a model for natural humic acid and is examined for its binding with three antibiotics (i.e., ciprofloxacin, norfloxacin, and tetracycline) as well as carbamazepine, a common marker for drugs as environmental contaminants. The binding of these drugs with the entrapped Leonardite humic acid are also compared to data previously obtained with a standard commercial preparation of humic acid (i.e., Aldrich humic acid). This binding is further evaluated under various pH, ionic strength, and temperature conditions to examine the types of forces involved in these interactions. The results are used to illustrate how microscale affinity columns can be used in examining and comparing biochemical interactions with complex binding agents (e.g., Leonardite versus Aldrich humic acid). The results also provide valuable information on binding by the model drugs with humic acids, as can be used to determine how such interactions affect the bioavailability and behavior of these and related contaminants in the environment.