| Antibiotics have broad-spectrum,strong antibacterial power,which play an important role in the treatment of various diseases.In recent years,because of the extensive use of antibiotics,more and more kinds of antibiotics have been detected in the environment,and the pollution of the environment is becoming more and more serious.Photodegradation is the main degradation mode of antibiotics in surface waters.In this paper,macrolide antibiotics?clarithromycin,roxithromycin,spiramycin and tylosin?have been chosen as the studying samples.The photodegradation of antibiotics were investigated in pure water and natural lake water exposed to high-pressure mercury lamp?250W?,xenon lamp?1000W?and sunlight.The photodegradation types,photolysis kinetics,influencing factors and quantum yield of antibiotics were explored.The combined effects and mechanism of dissolved substances on macrolide antibiotics in the water under simulated sunlight irradiation were revealed,and the changes of toxicity during the photolysis of four antibiotics under simulated sunlight were investigated.The main conclusions are as follows:?1?According to the results,the degradation was observed,at the fastest rate under high-pressure mercury lamp radiation,followed by xenon lamp and then natural sunlight according to the pseudo-first-order kinetics.The degradation constants of the four antibiotics were in different order under different light sources.Under ultraviolet and simulated sunlight,four antibiotics occurred direct photolysis and self-sensitized photolysis in pure water,and direct photolysis rate was much greater than the rate of self-sensitized photolysis.The quantum yields of SPI,ROX,CLA and TYL are:?1.44±0.11?×10-2??3.47±0.22?×10-3??6.31±0.19?×10-33 and?7.6±0.31?×10-3,respectively.The present results indicated that the photolytic rate constant?k?was negatively correlated with initial concentration?C0?.The p H has a significant effect on the photodegradation of four antibiotics.With the increase of solution p H,the k increased when exposed to UV irradiation,and fasted under alkaline conditions.Under simulated sunlight,SPI and TYL showed the slowest degradation rates under acidic conditions and the fastest under alkaline conditions.For ROX and CLA,the degradation rate constant of the antibiotic first increased and then decreased with the increase of solution p H.The degradation is the slowest under acidic conditions and fastest under neutral conditions.?2?The toxic changes of SPI,ROX,CLA and TYL on Selenastrum capricornutum toxicity were studied under simulated sunlight.The toxicity evaluation illustrated that some of the intermediate products formed were less toxic than SPI,while some of the intermediate products formed were more toxic than ROX?CLA and TYL.?3?The photodegradation kinetics of four antibiotics in lake water showed that the photodegradation accorded with the pseudo first-order reaction kinetics under UV light and simulated sunlight.The photolytic rate of SPI,ROX and TYL in pure water which exposed to UV light was lower than that in natural lake water,and the degradation of CLA in natural lake water is slower than pure water.Under simulated sunlight,the degradation rate of four antibiotics in natural lake water was greater than that in pure water.It can be seen that some dissolved substances in natural water have important effects on photodegradation of antibiotics.?4?Under UV irradiation,the presence of humic acid?HA?inhibited the degradation of SPI and ROX.HA promoted photodegradation of CLA and TYL at low concentrations,while accelerated the photolysis at high concentrations.Nitrate?NO3-?promoted the photodegradation of SPI and TYL,and inhibited the photodegradation of ROX.NO3-inhibited photodegradation of CLA at low concentrations,while accelerated the photolysis at high concentrations.Nitrite ion?NO2-?promoted the photodegradation of SPI and TYL and inhibited the degradation of ROX.NO2-accelerated photodegradation of CLA at low concentrations,while inhibited the photolysis at high concentrations.Iron ions(Fe3+)promoted the photodegradation of SPI,but inhibited the photodegradation of ROX,CLA and TYL.Ferrous ion(Fe2+)inhibited the photodegradation of CLA and TYL.Fe2+accelerated photodegradation of SPI at low concentrations,while inhibited the photolysis at high concentrations.Fe2+inhibited the degradation of ROX at low concentrations,and it had a significant promotion effect when the concentration increased.?5?Under simulated sunlight,HA had significant inhibition on the photodegradation of SPI and CLA.HA promoted photodegradation of ROX at low concentrations,and had a very pronounced inhibitory effect at high concentrations.Adding low concentrations of HA promoted the degradation of TYL,and when the concentration increased,the degradation of TYL was significantly inhibited.NO3-promoted photodegradation of SPI,ROX,and TYL.NO3-inhibited photodegradation of CLA at low concentrations,and also accelerated the photolysis at high concentrations.NO2-inhibited the photodegradation of four antibiotics.Fe3+promoted the photodegradation of SPI at low concentration,inhibited the degradation at high concentration.Fe3+inhibited the photodegradation of ROX,while promoted the photodegradation of CLA.Fe3+inhibited the photodegradation of TYL at low concentration,and had a promoting effect at a high concentration.Fe2+inhibited the photodegradation of SPI and ROX,and promoted the photodegradation of CLA.Fe2+inhibited the photodegradation of TYL at low concentration,and had a promoting effect at the high concentration.?6?A central composite design was used to investigate the compound effects of NO3-?HA and Fe3+on the photodegradation kinetics of SPI and TYL.The results were analyzed by software Design Expert 8.0.6.The results showed that the concentration of humic acid?HA?,the concentration of nitrate ion and the concentration of iron ions are the significant factors affecting the photodegradation of SPI and TYL under the simulated sunlight.To sum up,the photodegradation rates of macrolide antibiotics are different according to the pseudo-first-order kinetics under different light exposures.Macrolide antibiotics occurred direct photolysis and self-sensitized photolysis in pure water,and direct photolysis rate was much greater than the rate of self-sensitized photolysis.Photodegradation changed the toxic effect of antibiotics on Selenastrum capricornutum toxicity.The effect of soluble substances in water on the photodegradation of antibio tics has a great relationship with the structure of the material and the light source.This study is of great significance for understanding the migration,transformation and ecological effects of macrolides in water. |
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