R4 AM Occurrence and Fate of Pharmaceutical and Other Emerging Wastewater Contaminants in Aquatic Systems
Thursday, 17 November 2005: 8:00 AM - 11:40 AM in Ballroom 4

(LAT-1117-501368) Dissolved organic matter and the photochemical fate of pharmaceuticals and personal care products.

Latch, Douglas¹, Arnold, William¹, McNeill, Kristopher¹, ¹ University of Minnesota, Minneapolis, MN, United States

ABSTRACT- Recent work has demonstrated that photochemical degradation processes are important to the fate of many pharmaceuticals and personal care products (PPCPs) in sunlit natural waters. Dissolved organic matter (DOM) is intimately involved in these processes, acting as both sources and sinks of photochemically produced reactive intermediates (PPRIs). In this work, the role of humic substances in the photochemical degradation of three environmentally relevant PPCPs (ranitidine, cimetidine, and triclosan) was examined. Each of the PPCPs examined were photochemically labile, with various dependencies on DOM. Triclosan was rapidly degraded by a direct photolysis mechanism, with two toxic products, 2,8 dichlorodibenzo-p-dioxin and 2,4-dichlorophenol, formed in low yields. In photolysis experiments with added Suwanee River fulvic acid (SRFA), the DOM acted as a sink, with some of the triclosan coupling to the SRFA. Ranitidine also was degraded primarily by direct photolysis, though the PPRI singlet oxygen (¹O₂) contributed to ca. 10 % of the observed degradation rate. Cimetidine did not undergo direct photolysis, but was rapidly degraded by ¹O₂. Because ¹O₂ is involved in the fate of ranitidine, cimetidine, and other aquatic contaminants, fundamental studies were undertaken to examine the spatial distribution of ¹O₂ in irradiated aqueous DOM solutions. The microheterogeneous distribution of ¹O₂ in these DOM solutions was elucidated using hydrophobic trap-and-trigger chemiluminescent probe molecules in conjunction with the conventional hydrophilic probe furfuryl alcohol (FFA). The hydrophobic probes measured significantly higher [¹O₂] than did FFA, reflecting the relatively high local [¹O₂] within the DOM. A model was developed to calculate the ratio of [¹O₂] in the DOM and bulk aqueous phases for different size DOM particles. The results of these experiments suggest that hydrophobic pollutants that partition into DOM may be degraded more rapidly than would be predicted based on bulk aqueous phase PPRI concentrations.

Key words: photochemistry, pharmaceuticals, singlet oxygen, microheterogeneity