Adsorption Behavior Of Sulfamethoxazole In Soils And Impacts Of Cations And Pre-wetting

With the wide application,a great amount of antibiotics are discharged into the environment,resulting in potential environmental.risks.The sulfonamide antibiotics are frequently used and have been widely detected in the environment.These antibiotics are not only harmful to aquatic organisms,but also harmful to humans through the food chain enrichment.The soil and sediment are major sinks for organic contaminants,and they are the environmental media having important impacts on the transport and transformation of antibiotics.Sulfamethoxazole(SMX)is a typical(sulfonamide antibiotics).It is an ionic polar compound,which may exist in various forms.This property could result in very complicated adsorption mechanisms in soil and sediment.This study investigated the adsorption behavior of SMX in 11 soils.The correlation between individual soil properties and the apparent sorption coefficients was not significant,indicating that SMX sorption in the soil may be controlled by various mechanisms such as hydrophobic effect,cation exchange,surface area.In predicting the adsorption behavior,it should be taken into account physical and chemical properties of the soil.Metal ions come into the environment,through the application of fertilizers,sewage sludge,lime,and other industrial and municipal waste.The adsorption behavior of metal ions in the soil determines its bioavailability in the human and animal food chain,toxicity,as well as in the environment migration.And then study its co-adsorption with Ca2+,Mg2+,or Zn2+.The presence of Ca2+,Mg2+,or Zn2+ in the sorption system showed distinct influences on SMX adsorption.Among the three metal ions,Zn2+ dramatically increased SMX sorption,while Ca2+ and Mg2+ did not alter SMX sorption significantly.The sorption of SMX also decreased Ca2+ or Mg2 adsorption,but not Zn2.This phenomenon may be resulted from inner-sphere complexation of Zn2+ with soil particles,which consequently resulted in the occupation of the internal sites and replacement of Hi.This process led to the decrease of the negative surface charge,and decline of the repulsion between soil and SMX.But for metal ions,the presence of SMX will cover part of surface sites of Ca2+ or Mg2+ and little effect on Zn2+ because inner-sphere.In addition,changes in soil moisture conditions will affect the structure of the soil organic matter,pore size and soil wettability,therefore,will be affected correspondingly behavior and fate of pollutants in the environment.The natural variation in weather,such as dry weather,dump heavy rain will changes the water content in the soil,the impact of drying and wetting should also be considered in predicting the environmental behavior of pollutants.Wetting had a significant effect on the adsorption of low concentrations of SMX.The adsorbent which had wetting reduce the adsorption of SMX,maybe due to conformational changes in the air-dried organic matter.With noninfiltration,the polar groups towards internal and the hydrophobic groups towards external.Pre-wetting is a relatively slow process,three days is not sufficient to change the conformation of the organic matter completely.The presence of water molecules may also compete with the SMX At the same time,wetting has different effect on the various type of adsorbents,may be have relationship with nature of adsorbent.