| In recent years, as a kind of emerging environmental pollutants, pharmaceutical and personal care products (PPCPs) is causing particular concern. Ibuprofen (IBP) is a kind of non-steroidal anti-inflammatory drugs (NSADDs) which widely used to analgesia and treatment of rheumatic diseases. In the world health organization’s list of essential medicines, ibuprofen is a kind of important drugs, and in many places used as over-the-counter drug. Its prescribed daily dosage can be as high as 1200 mg/d. Its high excretion degree (70～80% of the therapeutic dose) as either a parent compound and/or in form of a metabolite. The traditional sewage treatment plants can only remove part of ibuprofen, therefore ibuprofen widely exist in the surface water environment.Photochemical degradation is an important way to remove most PPCPs in water environment. The current researches on IBP degradation are non-systematic. The photodegradation mechanism, photolysis products and the influence and mechanism of environmental factors are not yet clear. Especially the influence of suspended solids on photodegradation is less noticed. This study selects IBP as a model compound to research the photodegradation kinetics, photodegradation mechanism, photolysis products and the pathway in pure water, explores the influence of environmental factors on IBP photodegradation by simulating the natural water and analyzes the influence mechanism. This paper is aimed at understanding the environmental photochemical behavior of IBP thoroughly and providing theory basis for the environmental fate and ecological risk.A potassium ferrioxalate actinometer is used for measuring the quantum yield of IBP; effect of the initial concentration of IBP, the initial pH value of the solution and dissolved oxygen on IBP photodegradation are studied; and at last the photolysis mechanism of IBP is examined through a quenching experiment. The result shows that the mean wavelength (200～400 nm) quantum yield of the IBP photodegradation in pure water is 1.40. IBP photodegradation is subject to the pseudo-first-order kinetic model. Photodegradation rates of IBP will decrease while the initial concentration is increases. When the initial pH value of the solution is 7, the IBP (30 μmol/L) photodegradation rate constant is 0.01057 min-1. IBP photodegradation is facilitated under oxygen-free conditions and the photodegradation rate constant increases from 0.01057 min-1 to 0.01404 min-1. IBP photodegradation mechanism comprises direct photodegradation and self-sensitized photodegradation. During IBP photodegradation, the contribution rates of 3IBP*,·OH and 1O2 for the photodegradation are respectively 49.4%,21.8% and 38.6%.UPLC/Q-TOF-MS and GC-MS are used for identifying the products of IBP photodegradation in pure water and the photodegradation pathway is then deduced based on the structure of the products. The concentration variation of the photolysis products during IBP photodegradation is investigated and the photodegradation kinetics and quantum yield of them (thereof) are measured. The acute toxicity of the photolysis product is measured using photobacteria method. Results show that 13 main products are generated during IBP photodegradation. Dissolved oxygen has an influence on the concentration of partial photolysis products. The cumulative concentrations of 2-[4-(1-Hydroxy-2-methyl-propyl)-phenyl]-propionic acid and 4-Butyl-phenol in IBP photodegradation are too low to be detected directly. The photodegradation of the products is subject to the pseudo-first-order kinetic model. Wherein, the photodegradation of 4-Isobutyl-benzaldehyde is the fastest with the rate constant of 0.01229 min-1, while 1-(4-Isobutyl-phenyl)-ethanone the slowest with the rate constant of 0.00095 min-1. The relative inhibition rate of IBP for Photobacterium phosphoreum T3 microspecies is 17.2%; the relative inhibition rates of the six photolysis products are respectively 38.3%,45.0%,36.9%,65.9%,72.7% and 73.9%. An intermediate product with higher risk in terms of IBP is generated in the process of IBP photodegradation, resulting in the toxicity of the solution increasing.The effect of dissolved substances on IBP photodegradation in water is inspected and the mechanism is analyzed. Results indicate that nitrate radical facilitates the IBP photodegradation, nitrite radical inhibits the photodegradation while the effect of ammonium radical can be ignored. Halide ion inhibits IBP photodegradation in the condition that the pH value of solution is 7. Several studied metal ions and bicarbonate radical have different degrees of inhibition effect on IBP photodegradation. When the concentration of HA is 10 mg/L, the IBP photodegradation rate constant is 0.01377 min-1. HA facilitates IBP photodegradation. When the concentrations of HA are 20 mg/L and 30 mg/L, the IBP photodegradation rate constants are 0.00333 and 0.00300 min-1 respectively. HA inhibits IBP photodegradation obviously. When the concentration is increased from 20 mg/L to 30 mg/L, the inhibition effect is not enhanced significantly. Hydrogen peroxide significantly facilitates IBP photodegradation. Larger the concentrate of hydrogen peroxide is, more obvious the promoting effect is. Acetone has small influence on IBP photodegradation. Most dissolved substances such as nitrate radical, nitrite radical and humic acid can inhibit IBP photodegradation through light shielding effect.The mutual transformation between different forms of nitrogen or iron in water is simulated under the condition of different pE values to study the recombination influence of different forms of nitrogen or iron on IBP photodegradation. Prediction model of IBP photodegradation rate was established when NO3-, NO2- and Fe3+ coexist in the water through response surface methodology. At last, the IBP photodegradations in simulated fresh water and simulated seawater are studied. In the process of pE value increasing from 4.82 to 6.5, while the concentration of NO2- in the nitrogen system is increased unceasingly, the IBP photodegradation rate decreases gradually. In the process of pE value increasing from 6.5 to 8.15, while the concentration of NO3- in the nitrogen system is increased unceasingly, the IBP photodegradation rate elevates gradually. When the pE value is high, the actual promoting ratio is obviously less than the theoretic one, indicating NO3- and NO2- has antagonistic action. In iron system, Fe2+ turns into Fe3+ in the process of pE value increasing from low to high and the IBP photodegradation rate changes accordingly. Fe3+ and Fe2+ have synergistic effect. In the compound system of nitrogen and iron, when the pE values are 5.82 and 7.15 and the IBP photodegradation rate is obviously lower than that in pure water, the inhibition ratios are 47.26% and 41.79% respectively. When pE value is 13.05, the system promotes IBP photodegradation with the promoting ratio of 26.7%. If NO3-, NO2" and Fe3+ exist in water environment simultaneously, the response surface model can be used for estimating IBP photodegradation rate. The IBP photodegradation rates in simulated fresh water and simulated seawater are slower than that in pure water with the photodegradation rate constants of 0.00172 min-1 and 0.00928 min-1 respectively.Titanium dioxide, humin and sediment of the Pearl River and Haizhu Lake are selected to simulating the suspended solids in water so as to investigate their influences on IBP photodegradation. Results indicate that, titanium dioxide promotes the IBP photodegradation significantly, while humin, sediment of the Pearl River and sediment of Haizhu Lake obviously inhibit the IBP photodegradation.To conclude, IBP can have direct photodegradation and self-sensitized photodegradation in water, in which the photolysis products having stronger toxicity in terms of parent compound are generated. Meanwhile, IBP photodegradation is influenced by the dissolved substances and suspended solids in water. The study reveals the photolysis behavior and mechanism of IBP in water, having a great meaning in predicting the fate of IBP in water environment and evaluating the ecological risk. |
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