| The biogeochemical cycle of mercury(Hg)in a fish culture environment is important because it can accumulate in fish through bioaccumulation.Antibiotics are widely used to control fish diseases.The bioaccumulation of methylmercury and antibiotics in fish pose threat to human health after fish consumption by human beings.Antibiotics are easy to complex with metals,and mercury ions have high electronegativity.Therefore,antibiotics and mercury ions are likely to complex in the fish culture environment,which affects the morphological changes of the two.In this paper,oxytetracycline(OTC)and norfloxacin(NOR)were selected to study their complexion reaction with mercuric chloride(HgCl2)by changing the molar mass ratio of antibiotic to mercury solution,infrared.Spectroscopy were used to determine the complexion of antibiotics with mercury.Moreover,different environmental conditions were also impact factors to explore the changes in mercury form and antibiotic content after antibiotic and mercury complexion.Finally,the simulated fish culture environment was used to study the reaction of antibiotics and mercury in fish.Through the experiment and analysis,the following main conclusions are drawn:1.The results showed:Both OTC and NOR can complex with mercury,and when they complexed,OTC and NOR can bind free Hg2+,and the HgO content in the solution reduced.Therefore,the concentration of gaseous mercury(GHg)was significantly reduced,while the active mercury(RHg)complexed with Hg2+ in the solution,leading to the concentration of RHg is higher in antibiotics-treatment than that of the control group.Moreover,the THg content of the antibiotic solution was lower than that of the control group.Base on results from the infrared spectrum,the number of-CH2-and-OH at the same wave number changed.It is further confirmed that complexion reaction did occur after the antibiotic was mixed with Hg2+.2.The results of different influencing factors showed:Under alkaline conditions,Hg2+can easily combined with-OH and changed to Hg(OH)2.Therefore,the contents of THg,GHg and RHg in the solution decrease dramatically,especially for the GHg concentration decreased gradually with the increase of pH in solution.Light conditions promoted the formation of GHg,however,the shading conditions inhibited the formation of MeHg.In sea water,Cl-combined with Hg2+to form HgCl2,result in the GHg in sea water lower than that in fresh water,and the content of RHg and THg is higher in sea water than that in fresh water.No significance were observed for MeHg between sea water and fresh water.THg concentration in aerobic condition were higher than that in anaerobic conditions.In comparison,the GHg and RHg were higher anaerobic condition than that under aerobic conditions.and the difference of MeHg was not significant different between each groups.Dissolved organic matter(DOM)forms a flocculent complex with Hg2+.Therefore,THg,GHg,RHg and MeHg were lower than those parameter in solution without DOM.MeHg concentration generally increases with time.3.Environmental parameters also have effect on the degradation of antibiotics:the increase of pH in solution accelerated the degradation of the antibiotic.Antibiotics concentration decreased slowly under shading conditions.Both higher concentrations of Cl-in seawater and aerobic conditions accelerate the degradation of antibiotics.Higher concentration of DOM has a light shielding effect and inhibits the degradation of antibiotics.Antibiotics complex with Hg2+,the electrons easily migrate from antibiotics to Hg2+,the antibiotic eventually produces a methyl group and then reacts with the Hg0 formed by the electron to form methylmercury.4.There was no significant difference in THg and MeHg between the antibiotic treatment group and the control group,but the MeHg content(OTC:49.34ng/g,NOR:41.83ng/g)in fish supplemented with antibiotics were slightly lower than those in the control group(MeHg:53.31ng/g).These results indicated antibiotics may complexed with Hg inhibited MeHg formation in vivo of fish... |
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