A Research On The Degradation And Transformation Of Pharmaceuticals And Personal Care Products (PPCPs) In Nature Environment

As an emerging class of aquatic contaminants, pharmaceuticals and personal care products (PPCPs) have drawn popular concerns recently. Previous studies on the environmental fate of PPCPs have mostly focused on their behaviors during wastewater treatment processes in aquatic environments and in the sludge. However, little PPCPs is known about their behavior in nature environment. Photodegradation and adsorption of pharmaceuticals caused by sun irradiation may be of major significance in the natural elimination process. Metronidazole was selected as the model compound to investigate the the fate of PPCPs in environment. Results from the present study can help to assess the environmental risks of PPCPs.(1) The fate of metronidazole in surface water under sunlight (Wuhan, summer) irradiation was investigated. The effects of different parameters such as water quality, pH, familiar ions and initial concentration on photodegradation of metronidazole have been studied. The results indicated that metronidazole should undergo fast direct photolysis under sunlight irradiation. The photodegradation rate of metronidazole decreased obviously as the initial concentration increased. The photodegradation became fast under higher intensity of light source and when the wavelenth of the light source was close to the λmax of the analyte.(2) The effect of coexisting compounds on the fate of pharmaceuticals under solar irradiation was investigated. Tinidazole with similar structure to MET was employed as the analogue. The experimental results indicated that the presence of analogue which has similar photosensitive group to MET could produce inhibiting effect on the photodegradation of MET. Besides, the coexisting pharmaceuticals such as enoxacin, furazolidone, ketoprofen, naproxen, amoxicillin and diclofenac sodium with different absorption spectra to MET were selected to study the mechanism of effect. The results showed that the effect depended on the degree of overlapping absorption spectrum between MET and the coexisting pharmaceuticals. The relationship between the degree of the influence and the ultraviolet absorption spectra of coexisting pharmaceuticals found in this study could give an example in assessing the fate of pharmaceuticals in enviromantal water.(3) In this study, adsorption and degradation of four selected PPCPs, including metronidazole, tinidazole, caffeine and chloramphenicol were investigated in the laboratory using four agricultural soils in China and sediment from Changjiang river. The result indicated that adsorption of all tested chemicals in soils could be well described with Freundlich equation, and their adsorption affinity (Kf) on soil followed the order of chloramphenicol> caffeine> tinidazole> metronidazole. Generally, higher Kf value was associated with soils which had higher organic matter contents (except for caffeine acid in this study). Degradation of selected PPCPs in soils generally followed first-order exponential decay kinetics, and the half-lives were different with each other. Sterilization generally decreased the degradation rates, indicating microbial activity played a significant role in the degradation in soils. The degradation rate constant decreased with increasing initial chemical concentrations in soil, implying that the microbial activity was inhibited with high chemical loading levels.