Tuesday, November 14, 2006

Association Interactions Between Environmentally-Relevant Dissolved Organic Matter and Two Classes of Emerging Contaminants.

Nadia Carmosini and Linda Lee. Agronomy Dept, Purdue Univ, 915 W State St, West Lafayette, IN 47907-2054

In recent years, many organic chemicals from medical, agricultural, industrial, and commercial products have been recognized as emerging contaminants (ECs).  In soil-water systems, ECs of concern include a unique group of neutral hydrophobic compounds, the fluorotelomer alcohols (FTOHs), and a group of ionogenic compounds, human and veterinary antibiotics.  Residues of these ECs exist in municipal biosolids and animal manure (antibiotics only) making land application of these wastes a primary exposure route.  FTOHs and several antibiotic classes, such as the tetracyclines, are highly sorbed to soils, and thus expected to have limited mobility.  However, these antibiotics occur in surfaces waters around the world, and there is evidence that FTOHs are a source of globally distributed perfluorocarboxylic acids.  Recent studies suggest that binding to dissolved organic matter (DOM) may enhance the transport of these ECs.  Since contaminant-laden biosolids and manure are injected or surface-applied as a DOM-rich slurry, the DOM may act as a carrier for the ECs.  In this study, binding of an FTOH (8:2 FTOH) and two antibiotics (ciprofloxacin and a tetracycline) by DOM from environmentally-relevant sources (e.g., manure, biosolids, soil) under varying conditions (e.g., pH, metal concentration) is being quantified to evaluate the potential for DOM-enhanced transport.  Preliminary results for 8:2 FTOH and soil DOM indicate that binding constants (log KDOM) measured with an enhanced solubility technique range from 3.8 to 4.7.  These values are similar to reported soil organic carbon-normalized sorption coefficients (log Koc ~ 4.0) suggesting that hydrophobic interactions drive the association between 8:2 FTOH and DOM.  Binding constants measured to date for ciprofloxacin and Aldrich humic acid (pH 7) using a dialysis technique range from 5.49 to 5.93 and depend on DOM concentration.  These results indicate that site-specific mechanisms, such as cation-exchange or cation-bridging, are driving interactions between ionizable functional groups on the antibiotic and DOM.