Occurrence Characteristics Of Typical Contaminants In The Aquatic Environment Under "Urban-Rural" Gradient

Nowadays,the combined pollution of traditional contaminants and emerging contaminants in urban aquatic environment is becoming more and more serious,which significantly impacted the aquatic ecological security and human health.A total of 32 sampling sections were selected among urban area,suburb area and rural area with different intensity of human activities in Suzhou for this research.The traditional pollutants represented by nitrogen,phosphorus and heavy metals and emerging pollutants represented by antibiotic and antibiotic resistance genes?ARGs?were chosen as typical contaminants.ICP-MS,ultra-high performance liquid chromatography coupled with tandem mass spectrometry and high throughput fluorescence quantitative PCR were used to study the spatiotemporal distribution characteristics,environmental behaviors and potential risks of thses contaminants among three phases?water,suspended particulate matter and sediment?which based on the"Urban-Rural"gradient.The main results are as follows:?1?The water quality of Suzhou mostly belong to class III^V level.For DTN,the concentration was very high throughout four seasons,while the contents for NH₃-N,TP and COD_Mn were also high.Seasonal and regional differences were exhibited,however,the pollution level of urban area was higher than suburb and rural areas.Eutrophication assessment showed that most sampling sites were in a state of heavy eutrophication.The contents of TOC,TN and TP in the sediments were highest in winter,and the potential release risk of organic phosphorus was high.?2?Higher concentrations were detected for Mn,Zn and Cu while lower for Hg,Cd and Co in the aquatic environment.The total concentration of heavy metals was highest in rural area for water and sediments.For SPM,most heavy metals existed in the form of F1,whereas mostly in the form of F4 in the sediments,indicating that the incoming heavy metals were easily to be absorbed and migrated in the SPM primarily.As and Ni exhibited high carcinogenic risk in the water.The higher RAC values of Mn,Zn and Cd in the SPM and sediment suggested that they had higher mobility and bioavailability.Principal component analysis?PCA?exhibited that Pb,Sb,Cu,Zn,Cd and Cr in the sediments were mainly originated from human activities sources,while Co,V,As and Mn were mainly from natural background sources.?3?The total contents of antibiotic in the surface water,SPM and sediments were 39.28-2578.4 ng/L,22.94-6186.8 ng/g and 12.67-2248.7ng/g,respectively.Tetracyclines and quinolones were the major antibiotics pollution.The content of antibiotics detected had seasonal and regional differences,among which urban area was the most serious polluted.Suspended particulate matter played an important role in the migration of antibiotics.Significant correlation was found among the same category of antibiotics,suggesting that they usually had similar environmental behavior in the aquatic environment.Risk assessment showed that NFX,OTC,TC and DC in the surface water were in the middle risk level to high risk level.Higher risk was calculated in urban areas in spring and autumn,while higher risk in rural areas in winter and summer.The results of screening-out priority antibiotics showed that SDZ and EFX in the sediments had greater enrichment factor and potential risk.?4?A total of 262 species of ARGs were detected in sediment,the absolute abundance ranged from 1.55×10⁹ to 1.14×10¹¹ copies/g.The abundance level showed the seasonal variation of spring>summer>winter.The number of ARGs detected in winter was significantly larger than that in spring and summer,and the number of ARGs detected in urban areas was higher than that in suburb and rural areas.Aminoglycosides,beta-lactams and multidrug ARGs were the major types of ARGs,and antibiotic inactivation mechanism and efflux pump mechanism were the main resistance mechanisms of ARGs.The significant positive correlation between ARGs and MGEs or antibiotics indicated that MGEs could significantly promote the spread of ARGs and antibiotics could remarkably induce the production of ARGs.Generally speaking,urban aquatic environmental pollution showed significant seasonal and regional differences.The intensity of human activities had a significant impact on the occurrence and environmental behavior of typical contaminants.