Final 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 Amount: $316,600
RFA: Drinking Water (2000) RFA Text | Recipients Lists
Research Category: Drinking Water , Water Quality , Water
The objectives of this work were to evaluate transport processes affecting pharmaceutical movement in the environment, with emphasis on the influence of amphiphiles such as surfactants on the fate and transport of pharmaceuticals in the environment. The approach involved use of a combination of batch and column adsorption and desorption experiments involving environmentally relevant pharmaceuticals and amphiphiles (described below). In addition, a transport model was developed to model the movement of pharmaceuticals with complicated speciation behaviors to multi-site sorbents, to aid with interpretation of column experiments.
Work was conducted with a total of 9 pharmaceutical compounds, 11 sorbents, and 3 surfactants, all selected to represent a wide range of environmentally-relevant materials. Pharmaceuticals were selected from five different classes. Two quinolone antibiotics were selected because of their complicated speciation behaviors, and because of their widespread use, as well as reported strong interactions with aquifer materials. A hormone, 17-a-ethynyl estradiol, was selected because of concern about potential endocrine-disrupting behavior. An antiepileptic compound, carbamazepine, was selected because of its moderate hydrophobicity and environmental relevance. Two analgesics, acetaminophen and naproxen, were selected because of their widespread detection in natural and treated waters. And three beta-blockers, propranolol, metoprolol and nadolol, were selected both because of the limited information available about their interactions with environmental sorbents, and the potential for interactions as a result of their known surface active properties.
Sorbents were selected to include a number of natural and model materials. Included with the sorbents are one whole soil, one natural sand, and three model sorbents. In addition, a total of six minerals identified as components in the whole soil were studied for selected experiments for the purpose of assessing the roles of the individual components of the whole soil in adsorption.
Surfactants were selected to include one representative member of the anionic, cationic and nonionic surfactant categories. The anionic surfactant, sodium dodecylbenzenesulfonate, is an alkylbenzenesulfonate, one of the most widely used surfactant classes, and a class of surfactant likely to be found in wastewaters and environmental samples. Cationic surfactants are used in applications ranging from fabric softeners to hair conditioners. Although cationic surfactants would be expected to have relatively low mobility in the environment, they could nevertheless be present near wastewater outfalls or other high loading sites, and could be expected to potentially influence the movement of pharmaceutical compounds. Like anionic surfactants, ethoxylated nonionic surfactants are widely used in consumer products and detergents, and would be likely to be found in wastewaters and environmental samples.
For the work described here, specific combinations of selected materials were tested based on hypothesized interactions expected based on properties of the materials, as well as observations from preliminary experiments.
Summary of Findings
Major findings of the work are summarized below.
- Unlike many organic compounds, pharmaceutical hydrophobicity and solubility are not good indicators of adsorption/transport behavior for many compounds, either in the presence or absence of surfactants. This is particularly true for compounds with complicated speciation behaviors and compounds which can form strong complexes.
As an example, the quinolone antibiotics, nalidixic acid and norfloxacin, adsorb to a greater extent to multiple materials under some pH conditions than do the more hydrophobic compounds carbamazepine and 17-a-ethynylestradiol. For some classes of compounds hydrophobicity was important within the class, but not between classes. For example, the beta blockers propranolol, metoprolol and nadolol tended to adsorb to extents to a range of surfaces to extents consistent with their octanol-water partition coefficients. The analgesics acetaminophen and naproxen showed very little adsorption, consistent with their high solubilities, and were influenced by adsorbed surfactants to an extent consistent with hydrophobicity. For all compounds, the presence of surfactants influenced compounds differently, and differences were not necessarily predictable by adsorption behavior in the absence of surfactants.
- Environmental conditions (pH, ionic strength) and the presence of other compounds can have a strong effect on pharmaceutical adsorption and transport in the presence or absence of surfactants. Slight changes in environmental conditions were observed to produce substantial changes in mobility in selected systems.
Compounds like quinolone antibiotics which exhibit complicated speciation are most likely to exhibit variation in adsorption with changing pH. Both nalidixic acid and norfloxacin showed nearly two-order-of-magnitude variation in adsorption with changing pH. Further, many pharmaceutical compounds are capable of complexing with metals or other compounds (including surfactants), and the presence of these compounds is known to reduce solubilities and should increase adsorption. For example, the solubility of quinolone antibiotics is known to depend strongly on the concentration of multivalent ions in some pH ranges. Similarly, complexation of beta blockers with anionic compounds is known to occur and reduce solubility, and has been observed in this work to substantially increase adsorption.
- The mechanisms through which surfactants influence adsorption and transport of pharmaceuticals are pharmaceutical-compound-specific, and can vary with environmental conditions. (For example, one mechanism may dominate at low pH, another at high pH).
Experiments with quinolone antibiotics showed no indications of hydrophobic interactions with adsorbed surfactant layers, but adsorption of nalidixic acid at high pH was influenced by ion pairing with cationic surfactants. In other pH ranges, no effect was observed. Compounds such as acetaminophen, naproxen and carbamazepine showed effects consistent with hydrophobic adsorption/partitioning into adsorbed surfactant layers for cationic and nonionic surfactants. Beta blockers (which are themselves weak cationic surfactants) showed evidence of ion pairing with anionic surfactants, increasing adsorption.
- The amount of surfactant necessary to retard the movement of pharmaceutical compounds varies with mechanism. For example, systems where partitioning to adsorbed surfactant is important (e.g., the analgesics studied, carbamazepine) require relatively high surfactant loading; systems where ion pairing or complexation are important (e.g., quinolone antibiotics, beta blockers) will show effects when concentrations of surfactant are much lower (i.e., concentrations on the same order as pharmaceutical concentrations).
- Transport experiments with surfactants have shown that the influence of surfactants on pharmaceutical 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 is of particular interest because it has been observed on relatively ideal solid surfaces with little internal surface area.
Results of this work show that traditional methods of predicting fate and transport of contaminants based on physical properties are not adequate for many pharmaceutical compounds. Further, changes in environmental conditions and the presence of compounds such as surfactants can have substantial impacts on the movement of pharmaceuticals in the environment. A quantitative understanding of these factors is essential to predicting migration and associated risk of pharmaceuticals in the environment. The measurements resulting from this work provide substantial quantitative information which can be used to more accurately predict the movement of specific pharmaceuticals in the presence and absence of surfactants.
Journal Articles on this Report : 3 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.||
||Kibbey TCG, Paruchuri R, Sabatini DA, Chen L. Adsorption of beta blockers to environmental surfaces. Environmental Science & Technology 2007;41(15):5349-5356.||
||Lorphensri O, Sabatini DA, Kibbey TCG, Osathaphan K, Saiwan C. Sorption and transport of acetaminophen, 17α-ethynyl estradiol, nalidixic acid with low organic content aquifer sand. Water Research 2007;41(10):2180-2188.||