Study On Environmental Behavior Of Representative Sulfonamide Antibiotics In Soil-Vegetable System

Sulfonamide antibiotics were widely used for feed additives in Livestock and poultry breeding.Small part of the applied sulfonamides were residued in animal body after consumption,but most of them were excreted as parent compound or metabolite in urine and faeces,and then entered into the environment through multiple pathways.The pollution of sulfonamides in urine and faeces was increasingly serious with the rapid development of livestock and poultry industry.Although tremendous studies have been conducted on residues pollution of antibiotics in food origined from animals,little attention has been paid to the crops uptake of antibiotics from soil,which could enter human food chain and threaten human health.The plant uptake of sulfanomides from soil was affected by the sorption of sulfanomides to soil,and Vegetables are one of the largest edible agricultural products,therefore,it has theoretical and practical significance to study on environmental behaviors of representative sulfanomides in soil-vegetable sestem.In order to realize the pollution of sulfanomides in vegetables and soils,the survey on sulfanomides residues in vegetables and soils sampled from supermarkets,vegetable markets and vegetable fields in A city was conducted from April to October in 2009.The results showed that sulfadizine(SDZ),sulfamethazine(SMZ)and sulfamethoxazole(SMX)were detected in different vegetables,detection rates were 25.2%?97.1%and 25.0%and concentration ranges of detection were ND-8.6?g/kg,17.2-320.3?g/kg and ND-17.8?g/kg,respectively.The detection rate and average concentration of SMZ were the highest in three sulfanomides.The average concentrations of SMZ in different kinds of vegetables from high to low were root vegetable,leaf vegetable,Melon and fruit vegetable,solanaceous vegetable.SMZ in vegetable was distributed mainly in leaf and root,which could be the cause of high concentrations of SMZ in root vegetable and leaf vegetable.The results of soil pollution investigation showed that three sulfanomides were detected in different soils,detection rates from high to low was SMZ(53.8%)?SMX(28.2%)and SDZ(12.8%),and concentrations from high to low were SMZ(7.73 ?g/kg),SMX(4.85 ?g/kg)and SDZ(2.45 ?g/kg),respectively.The detection rate and average concentration of SMZ were the highest.The mobility and persistence of sulfanomides could be affected by the sorption of sulfanomides on soil,therefore,the sorption of three sulfanomides on different soil was studied.The results indicated that the adsorption isotherms of SMZ on three soils were well described by the Freundlich equation.The order of sorption capacity of SMZ on three kinds was yellow brown earth>lime concretion black soil>red soil.A positive correlation was found between sorption capacity of SMZ on soil and organic matter contents of soil.The sorption of three sulfanomides on yellow brown earth was different,The order of sorption capacity was SMZ>SMX>SDZ,the difference between pKa and logKow could be the main cause for various sorption.The sorption capacity of SMZ on soil decreased with the ion strength increase.The sorption of SMZ and SDZ on soil decreased with the increase of solution pH,the main causecould be the decrease of soil colloid Zeta potentials and change of SMZ form.The sorption of sulfanomides on soil was different under heavy metal pollution,there was no significant effect on sorption of SMZ and SDZ on soil under low concentrations(?1 mM)of Cu2+,and the sorption of SMZ and SDZ on soil increased after adding 5 mM of Cu2+between pH5 and pH7.2.With the increase of solution pH,the desorption of SMZ increased,In a certain pH range,the presence of Cu2+decreased desorption of SMZ on soil.There was fewer effect of Cd2+ on sorption SMZ on soil than Cu2+.The surfactants affected the sorption of sulfanomides on soil,the presence of CTAB?SDS and Tween80 at low concentrations decreased the sorption of sulfanomides on soil and at high concentrations the sorption increased slowly.In order to investigate the accumulation and metabolites of sulfanomides in vegetable,the uptake and effect factors of three sulfanomides from soil by pakchoi cabbage were conducted using pot experiment,metabolites of two sulfanomides in vegetable using water planting.The results showed that SMZ and SMX were easier to accumulate in vegetable than SDZ,The concentrations of SMZ in vegetable increased with the increase of SMZ concentration in soil.Compared with single sulfanomide pollution,SAs residues in soil decreased slowly and concentrations of SAs in vegetable was high under combined SAs pollution in soil,which could be caused by the significant decrease of bacteria and other microbials number in soil.The vegetable uptake of SMZ from soil decreased in the presence of CTAB and SDS,in the range of experiment concentrations,concentrations of SMZ in vegetable decreased with the increase of surfactant concentrations,the promoted transference of SMZ in rhizosphere soil from upper layer to sublayer in presence of surfactant,which resulted in the decrease of SMZ concentrations in rhizosphere soil and accumulation in vegetable.Acetylated metabolites of N4-SMZ and N4-SMX were detected in root,stem and leaf of vegetable after SMZ and SMX absorbed by vegetable,and the concentrations of two acetylated metabolites in root were significantly higher than that in stem and leaf,implied that root could be the main site of sulfanomides metabolism in vegetable.