Pharmaceutical Sorption to Model Soil Components

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0225696 MacKay Human and veterinary pharmaceutical compounds are detected increasingly in many environmental media, including soils, sediments, groundwaters and surface waters. It is unknown how humans and organisms will adapt to increasing environmental exposures to these bioactive compounds. Health effects of concern include the spread of antibiotic resistance, endocrine disrupting activity and adverse responses in non-target organisms.Hypothesis and Goal: In addition to interactions with natural organic matter, we hypothesize that pharmaceutical sorption to soils and sediments is governed by 3 mechanisms: (1) electrostatic attraction to oppositely charged sites on mineral surfaces; (2) cation exchange reactions with aluminosilicate clay minerals, and (3) surface complexation to iron and aluminum oxides. The ultimate goal of the proposed research is to quantitatively describe sorption of pharmaceuticals to clay and oxide soil minerals based on a mechanistic understanding of sorption phenomena.Methods: The research goal will be achieved by investigating pharmaceutical sorption to modelsorbents so that with sorbent phases present in real soil or sediment samples can be probedindependently. Five model sorbents will be used: 2- and 3-layer clays (kaolinite and montmorillonite), and iron and aluminum oxides. The high-use veterinary antibiotics oxytetracycline, ciprofloxacin, and FCQA and Enro-CO2 (substructures of ciprofloxacin) will be employed as test sorbates because agricultural antibiotic use represents the most concentrated pharmaceutical release to the environment.Results from this research can be used to predict pharmaceutical sorption from compound properties (solution complexation constant) and sorbent characteristics (surface chemistry at given pH/ionic strength).Significance and Benefits of Research: The proposed research will provide the first mechanistic model of solid-water partitioning of important veterinary antibiotic compounds. The quantitative models developed for high-purity sorbents can be adapted to develop a general partitioning model for any soil or sediment phase. Accurate descriptions of soil- and sediment-water partitioning will help to interpret observed pharmaceutical distributions in field surveys of ambient concentrations of pharmaceutical compounds, including our test sorbates, in surface and groundwater (USGS Toxic Substances Hydrology Program). Ultimately, the quantitative model of pharmaceutical sorption developed here can be used inan environmental fate model that, coupled with a toxicology model, will enable accurate assessments of the risk posed by the release of veterinary pharmaceuticals to aquatic environments.Educational Benefits: Integration of undergraduate students into research activities will provide an opportunity for these students to work closely with faculty to solve open-ended research problems. The proposed research will also form a foundation for future integrated research activities between Environmental, Pharmacy, and Agricultural programs at UConn and Duke.