Multimedia Fate Modeling And Ecological Risk Assessment Of Typical Antibiotics In Seasonal Frozen Rivers During Ice-covered Period

As a result of the widespread use of antibiotics,a large amount of excretion from human and animals containing antibiotic residues was discharged into the aquatic environments through domestic sewage and livestock aquaculture wastewater,leading to potential adverse effects on ecosystem health.Due to the low efficiency of removal of antibiotics,municipal wastewater treatment plants are considered to be the main source of antibiotics in the downstream rivers.Considering that the rivers in the ice-covered period have the characteristics of low temperature and slow flow rate,the transport and transformation processes of emerging contaminants in rivers will be affected to varying degrees.Therefore,it is of great significance to carry out researches on antibiotic residues in seasonally ice-covered rivers in northern China.To understand the environmental fate and ecological risk assessment of antibiotics with high detection frequencies and concentration levels in the ice-covered rivers in Northeast China,three antibiotics with large consumptions of sulfamethoxazole,lincomycin and florfenicol were selected as representatives of antibiotics in this paper.A Level IV multimedia fugacity model based on the fugacity method was established and applied to a seasonally ice-covered river receiving municipal wastewater treatment plant effluents,the Songhua River located in Northeast China.The results indicated that sulfamethoxazole,lincomycin and florfenicol were detectable in the ice-covered river and municipal wastewater treatment plant effluents.The detection frequency in the water compartment at all sampling sites was 100%,and the detection frequency in the ice compartment was lower.The detection ranges of concentrations of sulfamethoxazole,lincomycin and florfenicol in the ice compartment were n.d.-6.6,n.d.-8.7 and 2.1-16.8 ng·g^-1,respectively.The detection ranges of these concentrations in the water compartment were 2.0-23.0,5.9-52.5 and 12.7-32.0 ng·L^-1,respectively.The average concentration of the three antibiotics in the municipal wastewater treatment plant effluents was the highest.Sensitivity analysis indicated that the depth of the water and ice compartment and the flow rate play a key role in the environmental fate of the antibiotics in the ice-covered river receiving wastewater treatment plant effluents.The transport of sulfamethoxazole and florfenicol was mainly affected by the advection process and the water-ice compartment diffusion process,while the transport of lincomycin was mainly affected by the sediment-water compartment diffusion process.As the most important way to remove antibiotics from ice-covered rivers,the advection process has contributed more than 88%to the removal of all the three antibiotics.The targeted antibiotic concentrations in wastewater treatment plant effluents increased by an order of magnitude to 100 ng·L^-1 without affecting the environmental fate and concentration levels,and the concentration trend in each environmental compartment is consistent with the original concentration discharge trend.The targeted antibiotic concentrations in wastewater treatment plant effluents increased to 1μg·L^-1 could keep the targeted antibiotic concentrations higher than 10 ng·L^-1 in the receiving river from the wastewater treatment plant discharge source to downstream 25 km.The risk entropy values of the three antibiotics in the effluents outlet and the sampling sites near the wastewater treatment plant were higher,among which lincomycin mainly showed a moderate ecological risk of potential harm to aquatic ecosystem,and sulfamethoxazole and florfenicol mainly showed low ecological risk to aquatic ecosystems.By analyzing the monitoring concentrations of the three antibiotics,the antibiotics in the ice-covered river can be considered at a lower concentration level.The results of reliability verification of the fugacity model suggested that the Level IV multimedia fugacity model could successfully simulate the monitoring concentration within an average difference of one logarithmic unit,which proved that the mathematical model could effectively simulate the occurrence and fate of antibiotics in ice-covered rivers.