Uptake And Metabolism Of Four Typical Antibiotics In Leafy Vegetables

Antibiotics are introduced into agricultural plant-soil system by the application of manure or biosolids,or via irrigation using reclaimed wastewater.Antibiotics can enter the terrestrial food chains through plant uptake,which forms an alternative pathway for human exposure to antibiotics.Studies have shown that plant can absorb and accumulate antibiotics from the soil.However,previous studies mainly focused on detecting residues of the parent antibiotics,while ignoring the identification of antibiotics transformation products in plants.In this study,several edible leafy vegetables such as lettuce were used as model plants,and four ionic antibiotics include clarithromycin(CLA),sulfadiazine(SDZ),sulfamethoxazole(SMX)and trimethoprim(TMP)were selected as target antibiotics.Ultra-performance liquid chromatography quadrupole time-of-flight mass spectrometry(UPLC-Q-ToF-MS/MS)and Ultra-performance liquid chromatography-triple quadrupole tandem mass spectrometry(UPLC-QqQ-MS/MS)wereapplied for the detection of the uptake and metabolism of different antibiotics in different leafy vegetables under hydroponic condition.Under greenhouse condition,lettuces were exposed to the culture medium containing antibiotics(CLA,TMP,SDZ and SMX).CLA and TMP translocate from roots to leaves easier than SDZ and SMX,which is related to the structure and ionization form of antibiotics.Eight CLA metabolites,two SDZ metabolites,two SMX metabolites and 4 TMP metabolites were identified and characterized by high-resolution mass spectrometry non-targeted screening techniques in lettuce.The metabolites of CLA include oxidation,demethylation,methylation and descladinosylation products.The metabolites of SDZ and SMX were formylation product and acetylation product.Some of the metabolites of CLA and TMP were considered to be more toxic than their parent antibiotics.Phase II metabolites of SDZ and SMX can be converted back to parent antibiotics which may increase the level of antibiotics in plant.To investigate whether the metabolism of antibiotics in leafy vegetables is universal,the metabolism of antibiotics in six edible leafy vegetables(Leaf lettuce,Bitter chrysanthemum,Roman lettuce,Cilantro,Celery,Turnip)was investigated.Nine CLA metabolites and six TMP metabolites were identified and characterized by high-resolution mass spectrometry and non-targeted screening technique in different leafy vegetables,including phase I and phase II transformation products.Oxidation and demethylation were two major transformation pathways of CLA and TMP in different vegetables.The similar metabolic pathways of CLA and TMP in different leafy vegetables were regarded to associate with CYP450 enzymes.The results of this study showed that the metabolism of antibiotics in leafy vegetables was fairly universal.In order to comprehensively evaluate the health risks of antibiotics in plants,it is necessary to pay attention to the potential risk of their metabolites as well as to the parent antibiotics.