لخّصلي

Introduction Pharmaceuticals and personal care products (PPCPs) are the subject of increasing concern and scientific interest (1, 2). There are numerous reports concerning the occurrence of PPCPs in the wastewater treatment plants (WWTP), surface water, groundwater, and drinking water every year. Although they were generally detected in the ng-µg/L range, the continual infusion into the aquatic environment leads to the chronic exposure of nontarget organisms in the waters with largely unknown consequences (3, 4). As one subset of the PPCPs pollutant class, the amine drugs have been widely used and repeatedly found at concentration ranging from 0 to 2.5 µg/L (5-12). The structures of the amine drugs are shown in Figure 1. Until recently, except that direct photodegradation of propranolol was documented (13), fairly little is known about the environmental fate of these amine drugs. Recent studies have demonstrated that certain pharmaceuticals are susceptible to photodegradation in the aquatic environment (14-16). Therefore, direct and indirect photochemical reactions may contribute to the transformation of these compounds in sunlit surface waters. The numerous studies have identified humic substances (HS) and NO3 - as significant participants in the indirect photodegradation of pollutants (17, 18). Both of them can photogenerate the highly reactive, nonselective • OH thereby limiting the persistence of many pollutants that degrade relatively slowly by direct photolysis (19, 20). Additionally, photolysis of HS leads to the formation of other reactive species, including 1 O2 (21), O2 •-/HO2 • (22), H2O2 (23), eaq- (24), and the reactive HS triplet states (3 HS*), of which O2 •-/HO2 • , H2O2, and eaq- may play a minor role in the sunlit surface waters (25). Direct reactions between 3 HS* and organic substrates are likely to occur. They can be classified as energy, electron or hydrogen atom transfer reactions (25). Although there have been many studies proving the enhancement effects of HS on photolysis of the substrates (26), the photochemical mechanism underlying the degradation is still not well understood. To date, most of the concerns were the phenolic compounds for the enhanced degradationmediated by HS (17, 26-28), and some phenols have been demonstrated to be degraded via electron transfer mechanism (28). In this work, a class of amine drugs including primary, secondary, and tertiary amines was selected for study based on the likelihood that they would undergo photodegradation due to their structural moieties in the presence of HS. The photodegradation mechanism was elucidated in detail. The relationship between structure and activity for the reaction of amine drugs with HS was preliminarily examined in order to predict the propensity of various amines toward photooxidation in the sunlit surface waters. Major degradation products were identified by GC-MS analysis. The bimolecular rate constants (reaction with • OH and 1 O2) and apparent quantum yields of the indirect photodegradation for amine drugs were determined to predict the photochemical fate of amine drugs in the natural waters.