Solar Simulated Degradation Kinetics of Amoxicillin, Carbamazepine, and Diclofenac: A Fluorescence Excitation-Emissions Matrices Deconvolution Approach

There is limited knowledge of pharmaceuticals’ photochemical fate and transformation in the aquatic environment. This study devised a photoirradiation system to effectively study the degradation of amoxicillin (AMO), carbamazepine (CAR), and diclofenac (DIC). This study investigated the degradation of 1.00 mg/L of selected pharmaceuticals individually and in the absence and presence of 1.00 mg/L of Suwannee River natural organic matter (SRNOM). Fluorescence excitation-emission matrices (EEMs) and absorbance measurements were collected at 18-minute intervals to monitor the transformation of AMO, CAR, and DIC in aqueous solution throughout the 8.1-hour photodegradation experiment. Parallel factor (PARAFAC) analysis was used to deconvolute the excitation-emission matrices measurements to track the dissipation of the parent compound and observe underlying changes that resulted in the formation of intermediates and photoproducts. The fluorescence EEMs measurements and validated PARAFAC analysis were robust tools to track the photodegradation of parent pharmaceuticals and photoproducts. Several photoproducts of AMO, CAR, and DIC were observed by decomposing EEMs using PARAFAC analysis. Natural organic matter (NOM) suppressed the degradation of AMO and enhanced the degradation of DIC. The AMO degraded at a faster rate than DIC. Although CAR is not fluorescent, its photoproducts are fluorescent. The presence of NOM suppresses the degradation of CAR photoproducts. Excited states of NOM play a vital role in the degradation of parent compounds. The formation of the photoproducts is a severe environmental health concern because their toxicity is unknown. The study found that the spectrometric techniques can be used to investigate AMO, CAR, and DIC photodegradation in the presence and absence of NOM. Simultaneous fluorescence and absorbance measurements are used to raise awareness of water contamination by pharmaceuticals and their degradation products and guide regulatory authorities in informing water quality guidelines.