Photodegradation Of Typical Antibiotics In Ice And In Water:kinetic Comparison,and Effects Of Main Aqueous Constituents

Ice and snow are important environmental media,ice/snow photochemistry is therefore an emerging subject in environmental sciences.In order to reveal the differences and similarities between ice photochemistry and aqueous photochemistry,photochemical behavior of organic pollutants in ice and in water requires comparative studies.Antibiotics get attention for their "false persistence".In the study,we selected tetracycline antibiotics(TCs:tetracycline(TC)),sulfa antibiotics(SAs:sulfamethazol(SMT),sulfachloropyridazine(SCP))and fluoroquinolone antibiotics(FQs:enrofloxacin(ENR),difloxacin(DIF))as cases to compare photodegradation kinetics in ices and in waters from different water bodies under the simulated sunlight(?>290 nm)by considering the effects of dissolved substances(humic acid(HA),Cl-,NO3-and Fe(?)).The results show that under simulated sunlight(500W mercury lamp,?>290 nm),all five antibiotics undergo photodegradation and the photodegradation followed the pseudo-first-order kinetics.There are similarities and differences in the relative order of photodegradation of the same antibiotic in ice phase and water phase.For example,TC underwent the fastest photolysis in seawater ice followed by freshwater ice and pure-water ice;while TC photodegraded faster in freshwater and seawater than in pure water;SMT in the aqueous phase and the ice phase are in the order of seawater(ice)>fresh water(ice)>pure water(ice);SCP in the ice phase is in the order of seawater ice>freshwater ice>pure water ice,and in the aqueous phase is seawater>pure water>freshwater;The two fluoroquinolones in the aqueous phase and the ice phase are in the order of seawater(ice)>fresh water(ice)>pure water(ice).Further studies found that Cl-,HASS,NO3-and Fe(?)accelerated the photodegradation of TC in both ice and water phases.All the effects were enhanced with their increasing concentrations,however,there were differences for the two phases in the promotion degrees of each factor.In addition,in the ice phase,HASS,NO3-and Fe(?)can promote ENR,Cl-has no significant effect on ENR and DIF,and HASS showed a low concentration inhibition of difloxacin and high concentration promotes phenomenon;In addition,in the ice phase,HASS,NO3-and Fe(?)can promote the photodegradation of ENR,and Cl-has no significant effect on the photodegradation of ENR and DIF,the photodegradation of DIF by HASS showed low concentration inhibition and high concentration promotion;In the aqueous phase,HASS,NO3-and Fe(?)can promote the photodegradation of ENR and DIF,and Cl-has no obvious effect on ENR and slightly inhibits the photodegradation of DIF.The promotion and inhibitory effects of these constituents on the photolysis of antibiotics can explain the differences in the photodegradability of seawater ice,freshwater ice,pure water ice and organic pollutants in seawater,freshwater,and pure water.Furthermore,extrapolation of the lab data to the real environment indicated that photolytic half-lives of antibiotics,respectively in ice/snow surface and in surface water.The half-lives depended not only on the latitude and season,but also on the reaction matrixes(ice/water).The above results revealed the differences and similarities of antibiotics photochemical behavior in ice and in water uncovered by this study would better assessing the fate and risk of such emerging pollutants in the cold environments.