Pollution Characteristics And Risk Assessment Of Typical Antibiotics In Surface Water Environment Of Xi’an

As antibiotics were widely used,antibiotic pollutants have gradually entered the environment and have been detected in rivers,lakes and other water bodies in different regions.As a new first-tier city,Xi’an has such pollution inevitably,but there were little researches on the distribution characteristics of antibiotic pollution in the surface water environment.At the same time,microplastics,as a new type of pollutants in water,as well as the compound pollution with antibiotics have become the focus of environmental research recently.Based on this,the pollution characteristics of antibiotics in the surface water environment of Xi’an and the influence of microplastics on their content were carried out to analyze the ecological risk and factors influencing the migration of antibiotics,which provided a theoretical basis for surface water environmental protection and antibiotic pollution management in Xi’an.In this paper,the pollution characteristics of tetracycline(TC),sulfamethoxazole(SMZ),ofloxacin(OFX),roxithromycin(ROX)and chloramphenicol(CAP)in the surface waters and sediments of Wei river,Xi’an moat,Xingqing lake,Taohua lake and Kunming pool were identified.The acute and chronic aquatic ecological risk thresholds(PNEC)of antibiotics were obtained by species sensitivity distribution(SSD)combined with the evaluation factor method(AF).According to the measured concentration of antibiotics in the sampled water,the ecological risk was evaluated by risk quotients(RQs).With tetracycline as the representative antibiotic,the adsorption characteristics of tetracycline on three kinds of microplastics including polyethylene(PE),polystyrene(PS)and polyamide(PA)were studied under the conditions of different time,concentration,pH and ionic strength.The main research results are as follows:(1)Tetracycline(average concentrations of 20.13～53.17 ng/L)and ofloxacin(average concentrations of 13.43～34.98 ng/L)were the main antibiotics in water.The total detectable concentration of antibiotics in rivers was higher than that in lakes during the wet season(extremely 88.08 ng/L).The concentration of antibiotics in the dry season was 436.96 ng/L higher than in the wet season.Water was the main host medium of antibiotics.Compared with other major water areas(Taihu lake,Songhua river,Poyang lake and water source,etc.),the detection concentrations of five target antibiotics were at medium or below the average level.(2)There was a certain regularity in the distribution of antibiotics in surface water and surface sediments.Ofloxacin and roxithromycin conformed the cubic curve model,tetracycline and sulfamethoxazole conformed the quadratic curve model,and chloramphenicol had no obvious curve relationship between them.There was a significant negative correlation with dissolved oxygen(DO),and there was no significant correlation between the concentration of antibiotics,dissolved organic carbon(DOC)and pH in water.(3)The chronic ecological risk thresholds of tetracycline,sulfamethoxazole,ofloxacin and chloramphenicol was smaller than the acute ecological risk thresholds.The differences were 131.722 μg/L,43.109 μg/L,5.081 μg/L and 43.916 μg/L,respectively.The chronic ecological risks of ofloxacin in Wei river during the wet season and ofloxacin in Wei river,Xingqing lake,Taohua lake and Kunming pool during the dry season were at a high level(RQ>1),and the other antibiotics were at a medium or low-risk level(RQ=0.01～1).Chloramphenicol had no risk in different surface water environments during the wet and dry seasons(RQ<0.01).(4)Three microplastics of polyethylene,polystyrene and polyamide in water could adsorb tetracycline,thus affecting its migration and distribution.The adsorption process conformed to the pseudo-second-order kinetic model and reached the dynamic equilibrium after 24 h of adsorption.The process could be described by Freundlich adsorption isotherm,and there was no linear relationship between equilibrium concentration and equilibrium adsorption capacity.The order of adsorption capacity was polystyrene>polyamide>polyethylene,which was dominated by hydrophobic distribution and electrostatic attraction.The adsorption capacity of three microplastics in the experiment was the strongest in tetracycline solution when pH=5,and the adsorption amount of tetracycline decreased with the increase of pH thereafter.With the increase of Na+ strength,the adsorption amount of tetracycline increased first and then decreased.When there was no Na+ in the water environment,the adsorption of tetracycline on microplastics was the most obvious.