2004 Progress Report: The Influence of Amphiphilic Molecules on the Environmental Fate and Transport of PharmaceuticalsEPA Grant Number: R829005
Title: The Influence of Amphiphilic Molecules on the Environmental Fate and Transport of Pharmaceuticals
Investigators: Kibbey, Tohren C.G. , Sabatini, David A.
Institution: University of Oklahoma
EPA Project Officer: Page, Angela
Project Period: September 1, 2001 through August 31, 2004 (Extended to August 31, 2005)
Project Period Covered by this Report: September 1, 2003 through August 31, 2004
Project Amount: $316,600
RFA: Drinking Water (2000) RFA Text | Recipients Lists
Research Category: Drinking Water , Water Quality , Water
The objective of this research project is to evaluate transport processes affecting pharmaceutical movement in the environment, with emphasis on the influence of amphiphiles (e.g., surfactants, phospholipids) on the fate and transport of pharmaceuticals in the environment. The approach involves the use of a combination of batch and column adsorption and desorption experiments involving environmentally relevant pharmaceuticals and amphiphiles. In addition, a transport simulator (tracking both surfactants and pharmaceuticals and their coupled transport) will be developed to interpret experimental results and assess the potential impact of amphiphiles on the migration of pharmaceuticals. Work to be conducted is divided into four main tasks: (1) batch adsorption/desorption experiments; (2) column transport experiments with surfactants; (3) column transport experiments with Class II amphiphiles/vesicles; and (4) development of a coupled transport simulator.
To date, we have been making excellent progress in Tasks 1 (batch experiments) and 2 (column experiments) and have begun work on Task 4 (coupled transport simulator development). For the bulk of our work, we have selected five compounds representing major classes of pharmaceuticals and covering a range of physicochemical properties: acetaminophen (an analgesic); carbamazepine (an antidepressant); 17-α-ethinylestradiol (a hormone); norfloxacin (a fluoroquinolone antibiotic); and nalidixic acid (a quinolone antibiotic). Additional work also has been conducted with naproxen (an analgesic), and recent ongoing experiments are examining antihypertensive drugs.
Our experiments in Year 3 of the project focused on studying the adsorption and transport behavior of pharmaceutical compounds in the presence and absence of surfactants. Much of the work has been conducted on Canadian River alluvium, a natural material with an organic carbon content of 0.44 percent. In addition, selected experiments have been conducted with U.S. Silica F-95 sand, a fine-grained natural sand, and several additional model materials, including a high surface area silica and a high surface area alumina. The purpose of experiments with model materials has been to better understand the behaviors we have observed for both adsorption and transport with the more complex sorbents.
Adsorption experiments in the presence and absence of surfactants have shown increased adsorption of pharmaceutical compounds, with the magnitude depending on the surfactant and pharmaceutical studied, as well as experimental conditions such as pH. The surfactants used in experiments to date have included cetylpyridinium chloride ([CPC], a cationic surfactant) and a nonylphenol ethoxylate with nine ethoxylate units (NP9, a nonionic surfactant). In general, the results vary considerably from compound to compound, with some exhibiting adsorption behavior consistent with surface solubilization and others exhibiting behavior consistent with ion pairing in solution. In the absence of surfactants, the results indicate a one-to-two order of magnitude variation in adsorption affinity with changing pH for each of the two quinolone pharmaceuticals (nalidixic acid and norfloxacin), but no measurable adsorption for carbamazepine or acetaminophen. In the presence of surfactants, adsorption of acetaminophen and carbamazepine were enhanced to extents consistent with compound hydrophobicity, whereas adsorption of nalidixic acid and norfloxacin were not. At high pH values, the anionic species of nalidixic acid exhibited enhanced adsorption in the presence of the cationic surfactant, CPC.
Transport experiments with surfactants have shown that the influence of surfactants on transport is quantitatively consistent with batch adsorption experiments. Transport experiments have shown nonequilibrium adsorption behavior for several of the compounds studied, both in the presence and absence of surfactants. This observation has been of particular interest because it has been observed on relatively ideal solid surfaces with little internal surface area. It is speculated that the nonequilibrium behavior may result from simultaneous linked transport of the ionized and neutral forms of the compounds, and a preliminary transport model has been developed to study these effects further. Implications of nonequilibrium adsorption for transport of pharmaceuticals in the environment include unexpectedly early breakthrough of pharmaceutical compounds, as well as longer tailing at the end of the breakthrough curve, features that potentially could increase risk beyond that which would be expected from standard equilibrium transport models.
We will continue conducting the experiments described above, following the plan outlined in the original proposal. In Year 4 of the project, we will continue to conduct experiments with new compounds (antihypertensive drugs) and a range of minerals to better assess the effects of trace minerals in whole soils on overall adsorption and transport behavior. In addition, we will continue to improve our transport simulator, incorporating a more complex multisite nonequilibrium adsorption/desorption model. Finally, we plan to complete and submit the two journal publications currently in preparation.
Journal Articles on this Report : 1 Displayed | Download in RIS Format
|Other project views:||All 14 publications||3 publications in selected types||All 3 journal articles|
||Hari AC, Paruchuri RA, Sabatini DA, Kibbey TCG. Effects of pH and cationic and nonionic surfactants on the adsorption of pharmaceuticals to a natural aquifer material. Environmental Science & Technology 2005;39(8):2592-2598.||