Research On Antibiotic Distribution Characteristics And Photocatalytic Degradation In Water Environment Of Typical Cities In South And North China

The widespread use of antibiotics to treat human,animal and plant infectious diseases has resulted in serious antibiotic pollution in the aquatic environment,posing a potential threat to public health and aquatic organisms.Therefore,the problem of antibiotic contamination has received high attention worldwide.In this study,we aimed to investigate the pollution characteristics of 40 antibiotics in two important cities in South China and North China,assess the ecological risks of antibiotics in the water environment,and develop a photocatalytic method for efficiently degrading antibiotics at environmental concentrations.Due to the different climate and economic development levels in South China and North China,there are differences in the types,concentrations and temporal and spatial distribution of antibiotics.By comparing the distribution characteristics of antibiotics in the two cities,it is possible to reveal the effects of antibiotics systematically and comprehensively in different environmental media under different geographical conditions.The law of migration and transformation provides data and theoretical support for the pollution prevention and control of antibiotics in China.The occurrence,seasonal distribution,and ecological risk of 40 antibiotics in groundwater samples from a city in South China in summer and winter were studied.The total concentrations of antibiotics ranged from 34.73 ng/L to1344.17 ng/L in summer and 1.39 ng/L to 633.84 ng/L in winter,respectively.The concentration of antibiotics in groundwater was higher in summer than in winter.The summer rainfall increases,the surface water-groundwater interaction is stronger,and the content of antibiotics with stronger water solubility which were easier to migrate increases in groundwater,such as sulfameter（detection rate:40.32%）and sulfamethoxazole（detection rate:40.32%）.The concentration range of sulfameter and sulfamethoxazole is～123.61 ng/L and～253.07 ng/L,respectively.Studies have shown that antibiotics such as sulfamethazine,sulfamethadiazole,norfloxacin,ciprofloxacin and danfloxacin have a significant promoting effect on the proliferation of ARGs.In addition,the promotion of ARGs diffusion by water quality parameters such as SO₄^2-,F^-,TDS,DO and p H cannot be ignored.The sum of antibiotic concentrations in the water circulation system of a city at North China,including surface water,groundwater,and sediment was12.71～260.56 ng/L,～196.12 ng/L,and 38.03～406.31 ng/g,respectively.In surface water and sediment,cephalosporins and quinolones were the primary antibiotics,accounting for 45%and 16%of the total antibiotic concentrations in surface water and for 62%and 32%of the total antibiotic concentrations in sediment;this suggests a significant interaction between the two media.The antibiotic concentration was the highest in shallow groundwater at depths of<50m（mean concentration of 79.22±56.46 ng/L）,indicating that surface water was a possible source of antibiotic contamination in groundwater.Amoxicillin and sulfamethoxazole presented the higher risk in both surface and groundwater and should be controlled as a priority.Moreover,the selection pressure of antibiotics on ARGs was discovered in the sediment in this city,because the enrichment of sul A was significantly correlated with spiramycin and lincomycin and the enrichment of bla _OXA-1 was significantly correlated with roxithromycin,ciprofloxacin,ofloxacin,and sulfapyridine.In this study,the photocatalytic oxidation method based on the commercially available titanium dioxide（Ti O₂）,which is a cheap,easy to obtain,non-toxic and highly stable catalyst,was developed for the controlled by priority antibiotic in two cities of sulfamethoxazole degradation.Moreover,in this photocatalytic oxidation process,sodium dithionite(DTN,S₂O₄^2-)was selected as the free radical generating source.The results show that the efficient degradation of sulfamethoxazole was achieved by using Ti O₂ as a catalyst to activate DTN.In the Ti O₂/DTN system,100%efficient removal of sulfamethoxazole can be achieved within 1 hour.By exploring the effects of catalyst dosage and DTN concentration on the degradation efficiency,the optimal reaction conditions were finally determined to be 5 mg Ti O₂ dosage and 20:1 molar ratio of DTN to sulfamethoxazole.Sulfamethoxazole can be efficiently removed under alkaline p H conditions（7.0～11.0）and significantly inhibited under acidic conditions（1.0～5.0）.In the presence of bicarbonate,the degradation of sulfamethoxazole is basically unaffected,and it has a promoting effect when the concentration is50～200 mg/L.However,in the presence of nitrate,chloride and humic acid,the degradation of sulfamethoxazole was significantly inhibited,and the inhibition increased with the increase of the concentration.Through the quenching and trapping experiments of free radicals,it is proved that the main active free radicals are sulfate radicals,as well as hydroxyl radicals and singlet oxygen.