Study On The Migration Law Of Tetracyclines And Sulfonamide Antibiotics In The Freeze-Thaw Process

China is a major country in the production and use of antibiotics,with the dosage of tetracycline antibiotics and sulfonamide antibiotics ranking first among antibiotic drugs.Antibiotic drugs have a high persistence in water,and their half-life increases with the decrease of temperature.The decrease in winter water temperature leads to a decrease in the rate of biodegradation and hydrolysis in the ice water,and in winter,due to the presence of ice sheets,the rate of photolysis in the under-ice water also significantly decreases.The freezing of water in winter can lead to the migration of tetracycline antibiotics and sulfonamide antibiotics into under-ice water,resulting in the enrichment of tetracycline antibiotics and sulfonamide antibiotics in under-ice water.The melting of ice in spring will cause the concentrated release of tetracycline antibiotics and sulfonamide antibiotics captured in the ice in a short period of time,causing a great impact on the water environment.The driving force of material motion is energy.The change in energy can cause water molecules to rearrange and combine into ice clusters during the freezing process,and the energy difference between the ice and water phases leads to the migration of tetracycline antibiotics and sulfonamide antibiotics.Ice melting is the process by which antibiotic molecules and water molecules detach from the ice body,accompanied by bond breakage.Different types of bonds have different bond energies and require different amounts of energy to break.In order to investigate the migration patterns of tetracycline antibiotics and sulfonamide antibiotics during freeze-thaw process,tetracycline(TET),chlortetracycline(CTC),oxytetracycline(OTC),doxycycline(DOX),sulfapyridine(SP),sulfadiazine(SD),sulfamethoxine(SM2),and sulfaquinoxaline(SQ)were selected as the research subjects for indoor simulation experiments.By exploring different freezing time,the migration rule of tetracycline antibiotics and sulfonamide antibiotics in the freezing thawing process at different initial concentrations and different freezing temperatures was studied.Quantum chemistry calculations were carried out at the molecular level through Gaussian operation and RDG analysis,revealing the reasons for the migration of tetracycline antibiotics and sulfonamide antibiotics in the freeze-thaw process,and further clarifying the migration mechanism of tetracycline antibiotics and sulfonamide antibiotics in the freeze-thaw process of water.The experimental research results are as follows:1.Under different freezing time,freezing temperature,and initial concentration conditions,all eight antibiotics will migrate into under-ice water.And it was found that the concentration of antibiotics in under-ice water during the freezing process is directly proportional to the freezing time.As the initial concentration increases,the concentration of antibiotics in under-ice water increases;As the freezing temperature decreases,the concentration of antibiotics in under-ice water increases.Under the same freezing conditions,the migration of tetracycline antibiotics is greater than that of sulfonamide antibiotics.2.Through Gaussian calculation,it is found that the binding energy of eight antibiotics in the ice phase is less than their binding energy in the water phase.Due to the existence of energy difference,eight antibiotics will migrate from the ice to the under-ice water during the freezing process;It is found that the difference of the binding energy of tetracycline antibiotics is greater than the difference of the binding energy of sulfonamide antibiotics,which is consistent with the experimental results.3.There is a phenomenon of concentrated release of eight antibiotics during the ice melting process.In the early stage of ice melting,the concentration of antibiotics in the ice melting water is relatively high,but as the ice melting process progresses,the concentration of antibiotics in the ice melting water rapidly decreases.Antibiotics in ice may not be completely released in the early stages,and some antibiotics may occasionally be detected at extremely low concentrations in the later stages.4.Through RDG analysis,it was found that the interaction between antibiotic molecules and ice molecules is van der Waals force,while the interaction between various water molecules inside the ice molecules is hydrogen bonding.The energy required for van der Waals force to break is much smaller than that of hydrogen bonds,so in theoretical calculations,antibiotic molecules will take priority over water molecules to break away from the ice.However,due to the energy applied during the ice melting process far exceeds the energy required for hydrogen bond breaking,both water molecules and antibiotics detach from the ice body at the same time.