Study On Photodegradation And Toxicity Of Tetracycline Antibiotics In Water

In recent years,due to the extensive use of antibiotics,it has been detected in various environmental media such as lakes,rivers,groundwater,soil,etc.,which has caused widespread concern about the residual effects of antibiotics in environmental media and the hazards caused.Photodegradation is an important degradation pathway of tetracycline antibiotics（TCs）in the water environment.In view of the accumulation of TCs in water and the current status of antibiotic use,this paper studies tetracycline antibiotic（TC）,chlortetracycline（CTC）,oxytetracycline（OTC）and Doxycycline（DC）and other four tetracycline antibiotics photochemical behavior in water:under high-pressure mercury lamp and xenon lamp irradiation,water p H,humic acid,nitrate,Metal ions（iron ions,calcium ions,magnesium ions）,active oxygen quencher on the photodegradation of TCs.The photodegradation efficiency and half-life of tetracycline antibiotics in the water of Wulungu Lake were also discussed.At the same time,the influence of TCs on the growth of Crescent Crescent Algae was also explored.1.TCs has a strong absorption of light below 450nm,and can produce direct photodegradation.PH has a great influence on the degradation rate.The larger the p H is,the faster the degradation rate is.When p H=10.0,the difference between the photodegradation rate constant of TCs and p H=6.0 is more than 20 times.Under different p H conditions,the photodegradation reaction accords with the first-order kinetic model.2.Under the same conditions,the degradation rate of TCs under UV irradiation is higher than that under xenon irradiation.3.In ultrapure water,NO₃^-,Fe³⁺can promote the photodegradation of TCs,and with the increase of concentration,the degradation rate increases and the half-life shortens.Humic acid can promote the degradation of TCs in lower concentration,while higher concentration can inhibit the degradation of TCs.At p H=8.5,NO₃^-and Fe3+can promote the degradation of TCs.Compared with ultrapure water,NO₃^-and Fe3+can promote the degradation efficiency of TCs.Humic acid can promote the degradation of TCs in low concentration and inhibit it in high concentration.However,compared with the influence of humic acid in ultra pure water,the influence of humic acid on the degradation of TCs in alkaline condition is less.4.In ultrapure water,Ca²⁺can promote the photodegradation of TCs.The higher Ca²⁺concentration is,the more obvious the promotion is.Mg²⁺can inhibit the photodegradation of TCs,and the higher Mg²⁺concentration is,the stronger the inhibition is.When p H=8.5,Ca²⁺,Mg²⁺can inhibit the photodegradation of TCs.The higher the concentration of Ca²⁺,Mg²⁺is,the stronger the inhibition is.The reason why Ca²⁺,Mg²⁺affect the degradation rate of TCs is that they can complexate with TCs,change the molecular conformation of TCs,make TCs more stable or easier to depolymerize.5.The half-life of water photodegradation in Wulungu Lake is between 73-210 min under outdoor sunlight.6.The degradation rate of TCs in the simulated sunlight is slower than that in the outdoor sunlight.The degradation rate of TCs in the deionized water is smaller than that in the outdoor sunlight,which may be related to the substances in the water(such as NO₃^-,Fe³⁺,etc.).7.The study on the toxicity of CTC,DC,OTC and TC to p.capricornus showed that the products with lower toxicity to p.capricornus were produced in the process of OTC photodegradation,and the products with higher toxicity to p.capricornus were produced in the process of DC,CTC and TC photodegradation,and the toxicity of these four antibiotics to L.ceratoides is:TC>DC>CTC>OTC.