2003 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, 2002 through August 31, 2003
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 an 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 (development of a coupled transport simulator). For our initial work, we have selected four compounds representing major classes of pharmaceuticals and covering a range of physicochemical properties: acetaminophen (an analgesic); carbamazepine (an antidepressant); 17--ethinylestradiol (a hormone); and nalidixic acid (an antibiotic). Additional work also has begun with naproxen (an analgesic) and norfloxacin (an antibiotic).
Our experiments in Year 2 of the project have 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 was 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 up to factors of two or more, with the magnitude depending on the surfactant and pharmaceutical studied, as well as experimental conditions. The surfactants used in experiments to date have included cetylpyridinium chloride (a cationic surfactant) and a nonylphenol ethoxylate with nine ethoxylate units (NP9, a nonionic surfactant). In general, results have tended to parallel pharmaceutical solubility and Kow (i.e., pharmaceuticals with low solubilities or high Kow values exhibit a greater increase in adsorption in the presence of surfactants). Interestingly, solubility and Kow do not appear to be uniform predictors of pharmaceutical adsorption in the absence of surfactants. Although high solubility compounds such as acetaminophen tend to adsorb very weakly to solid surfaces, as might be expected, the low solubility compound carbamazepine (S = 17.7 mg/L; log Kow = 2.45) adsorbs very weakly. Nalidixic acid, which has a higher solubility and lower Kow than carbamazepine (S = 100 mg/L; log Kow = 1.59), adsorbs to a much greater extent under similar conditions.
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. Ongoing work is evaluating this hypothesis. 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 could potentially increase risk beyond that which would be expected from standard equilibrium transport models.
We will continue to conduct experiments as described above, following the plan outlined in the original proposal. In Year 3 of the project, we anticipate collecting considerable data with a wide range of surfactant/pharmaceutical combinations. We also will continue work on the transport simulator, and begin work with Class II amphiphiles.