Researches On The Adsorption-Desorption Characteristics Of Sulfonamides In Dianchi Lake Wetland Soils

Sulfonamides,as one of the broad-spectrum antibiotics,are widely used in agricultural production and medical fields.In the process of using sulfonamides,most of the drugs will be excreted with animal feces and urine to pollute the environment,and the environmental pollution caused by sulfonamides is becoming more and more serious.Dianchi Lake is the largest water lake in Kunming City,Yunnan Province,which plays an important role in the economic and social development of Kunming and even the whole province.Dianchi wetland is an ecological green barrier and a buffer between land and water,which plays an important role in conserving water and purifying water quality.In view of the current situation of blind use and abuse of sulfonamides antibiotics and their serious harm to the environment,this study selected wetland soils from 8 sites in Dianchi Lake Basin: The soils of Xiaigeng,Haifeng,Dongdahe,Xihua,Dounan,Laoyuhe,Caohai and Haidong wetlands were used as experimental soils,and sulfadiazine,sulfamethoxazole and sulfapyridine were used as experimental sulfonamides.The adsorption and desorption characteristics of three sulfonamides in the soil of Dianchi wetland and the influence of environmental factors were studied by kinetic,isotherm and thermodynamic tests.The main research results are as follows:(1)The adsorption-desorption process of three sulfonamides in wetland soil was divided into three stages: fast,slow,and equilibrium,and all of them reached the adsorption-desorption equilibrium within 24 h.The Freundlich,Langmuir and Henry isotherm models were all suitable to describe the adsorption behavior of sulfonamides in wetland soil,and the Freundlich isotherm model could better describe the desorption process of sulfonamides from wetland soil.Sulfapyridine had a better interception effect than sulfadiazine and sulfamethoxazole in wetland soil,but the three sulfonamides were easy to desorb from wetland soil with strong migration ability,and had a greater potential pollution risk to surface water and groundwater resources.(2)There was a phenomenon of competitive adsorption among the three sulfonamides simultaneously existing in wetland soil,and sulfapyridine was the most competitive among the three sulfonamides.The adsorption-desorption behavior of sulfonamides in the mixed system showed antagonistic adsorption and cooperative desorption.(3)The chemical adsorption process of sulfonamides occurred in wetland soil.The amino(-NH)functional group,O and N-heteraromatic ring of sulfonamides mainly adsorbed on wetland soil through hydrogen bonding and π-π interaction with-OH,C-O,-OH,C=C,C=O functional groups.(4)Environmental factors significantly affected the adsorption-desorption behavior of sulfonamides in wetland soil.p H affected the adsorption-desorption behavior of sulfonamide antibiotics in wetland soil by affecting the existence form of sulfonamide antibiotics.With the increase of solution p H,the adsorption capacity of sulfonamide antibiotics in wetland soil decreased,and the desorption capacity increased.Citric acid and malic acid had bidirectional effects on the adsorption and desorption behavior of sulfonamides in wetland soil.With the increase of citric acid concentration,the adsorption of sulfonamides in wetland soil showed low concentration stimulation to promote adsorption,and then inhibit adsorption.With the increases of malic acid concentration,the adsorption of sulfonamide antibiotics in wetland soil showed a trend of stimulating adsorption at low concentration and inhibiting adsorption at high concentration.The addition of corn stover biochar significantly promoted the adsorption capacity of sulfonamide antibiotics in soil,and significantly inhibited the desorption behavior.The adsorption capacity of wetland soil to sulfonamide antibiotics increased with the increases of biochar content,while the desorption capacity decreased with the increases of biochar content.