Chapter 3.2 Transformation of pharmaceuticals in the environment: Photolysis and other abiotic processes

Abstract

Publisher Summary For a pharmaceutical compound to enter the aquatic environment unaltered after having passed through a human or animal digestive system, it must be resistant to acid- and enzyme-promoted hydrolysis reactions. The compound must be resistant to other enzyme catalyzed transformation reactions if it is to be released to the environment in its original form. This chapter focuses on abiotic processes that lead to the transformation of pharmaceutical compounds in environmental systems. As the pharmaceutical compounds or their degradates emitted in wastewater effluent are expected to be resistant to hydrolytic processes, direct and indirect photolysis is the only relevant abiotic loss processes in sunlit aquatic systems. The two types of photolysis processes occurring in aquatic systems are direct photolysis and indirect photolysis. In direct photolysis, the target contaminant absorbs a solar photon. Whereas, in indirect photolysis mechanism, the target does not need to or is unable to absorb light because another chromophore in the system such as dissolved organic matter acts as a sensitizing species. Photolysis reactions lead to multiple reaction products produced by various competing/parallel pathways. Thus, identification of photolysis reaction products is laborious and usually requires isolation of the compounds and analysis with sophisticated mass spectrometers.