Effect Of Ionization Speciation On The Plant Uptake Of Antibiotics

In recent years,an increasing trend was observed globally in the consumption of antibiotics.China is the largest producer and user of antibiotics in the world,and the total antibiotic usage in China for 2013 was estimated to be approximately 162000 tons.The uptake of antibiotics in soils from wastewater or animal manures to crops is closely related to their physicochemical properties,but the mechanism of plant uptake of ionizable antibiotics is not clear yet.Therefore,an insight into the relationship between the accumulation of antibiotics in edible crops and their ionization speciation can provide a scientific basis for the human health risk assessment of antibiotics.In this study,seven frequently occurring antibiotics were selected for their analysis in lettuce,and the relationship between plants uptake and their ionic speciation was investigated by adjusting the pH values of the nutrient solution grown under hydroponic conditions.On the basis of previous work,the sample pretreatment process investigated the effect of EDTA on the extraction of antibiotics,and the optimization of the purification process was combined with HPLC-ESI-MS/MS detection.In this study,PSA and EDTA were examined to purify impurities in sample preparation process,and PSA demonstrated better recoveries.In addition,the optimized analysis method was tested by the spiked recovery experiment for the lettuce samples.The recovery rates of antibiotics in the leaf samples was between 95%and125%with RSD<10.2%,and the recovery rates in the root samples was between 90%and120%with RSD<8.3%.Therefore,the analysis method has good performance in the extraction of multiple antibiotics in lettuce.Lettuce plants were cultured in nutrient solutions containing antibiotics at 50?g/L,and five pH values of 5,6,7,8 and 9 were selected to test of uptake of targeted antibiotics by lettuce.With the pH of the nutrient solution increasing,the accumulation of sulfadiazine and sulfamethoxazole in roots decreased significantly.Ionic speciation analysis showed that neutral species of sulfonamide were easily absorbed by roots.Due to the change of the pH value inside and outside in root cell,sulfonamide would ionize in the cell and produce an electrical repulsion with the negatively charged cell membrane,thus it was trapped in the root cell and inhibited to be transported to acrial part.Because the dominantly speciation inside and outside the cell is neutral,florfenicol can be more easily transported to the upground tissue via transpiration,therefore it demonstrated relatively larger translocation factor than other antibiotics.Correlation analysis of logBCF and logD_ow of targeted antibiotics showed that sulfadiazine,sulfamethoxazole,trimethoprim,and clarithromycin have strong positive correlations between their logBCF_root and logD_ow with the correlation coefficient>0.8,it was proved that the root uptake of these four antibiotics were mainly related to their neutral species.