Photochemical Fate of Pharmaceutical Compounds Discharged and Detected in Natural Waters

Project Staff: 

Principal Investigators: William Arnold, Assistant Professor, Department of Civil Engineering; K. McNeill, Department of Chemistry, University of Minnesota

Additional Staff: J. L. Packer, Research Assistant, Department of Civil Engineering; D. E. Latch, and A. L. Boreen, Research Assistants, Department of Chemistry, University of Minnesota

Funding: 

USGS-WRRI 104G National Grants Competition

Project Duration: 

September 2001 - August 2003

Summary: 

Recent studies have detected numerous pharmaceuticals and personal care products (PPCPs) in US surface waters. The potential environmental impact of these chemicals will be dictated by their persistence in the environment and the biological activity of any degradation products. One potential loss process for pharmaceuticals and personal care products is photodegradation. In this work, the direct photolysis and indirect photolysis (hydroxyl radical mediated and singlet oxygen mediated) of selected PPCPs was investigated. To date, the fate of the antacids cimetidine and ranitidine hydrochloride and the antimicrobial compounds triclosan and chlorophene have been studied. All the compounds studied react with hydroxyl radical at nearly diffusion limited rates, but given the low concentration of hydroxyl radical in natural waters, other processes appear to be more important. The heterocyclic groups in cimetidine and ranitidine hydrochloride are susceptible to attack by singlet oxygen. Ranitidine hydrochloride is subject to direct photolysis while cimetidine is not. Direct photolysis occurs rapidly for triclosan and chlorophene when these compounds are present in the deprotonated phenolate form. These compounds also react with singlet oxygen, but preliminary results indicate that direct photolysis is the dominant photo-initiated loss process. The direct photolysis of triclosan at pH >8.0 leads to the formation of 2,8-dichlorodibenzodioxin in yields ranging from 1-10%. This result underscores the importance of identifying the transformation products and not just the degradation rates. (Findings from this research were featured in the Minneapolis Star Tribune and St. Paul Pioneer Press on April 14, 2003.)