Ecological Toxicity Of Selected Antibiotics On The Embryo Of Xenopus Tropicalis

In the past half-century, antibiotics have been extensively used as human therapy,veterinary medicine, and as husbandry growth promoters. Intensive aquaculturesystems, characterized by high stock density and volume, have undergoneunprecedented growth. A significant portion of antibiotics in human and animals isexcreted and released into the aquatic environment through many pathways. To date, agreat variety of antibiotics have been detected in various aquatic environments,including wastewater, surface water and groundwater, even drinking water.Antibiotics in waters will lead to adverse ecological and health impacts due to theirtoxic effects to aquatic organisms. The occurrence and ecological risk of antibioticresides in the aquatic environment have caused great public concerns among theenvironmental researchers and engineers. In this paper, we have selected and studiedthe effects of three widely used antibiotics (chloramphenicol, erythromycin andtetracycline) on the growing Xenopus tropicalis embryos. The results obtained mayprovide valuable information for understanding the environmental safety of selectedantibiotics. The primary contents and results in this study as follows:Acute test, the embryos of Xenopus tropicalis were exposured from the stage NF11-12to0.5-1.5g/L chloramphenicol (CAP),0.5-1.5g/L erythromycin (ETM), and0.01-0.5g/L tetracycline (TC) for72h The surviving embryos were anaesthetizedwith MS-222and fixed in formaldehyde for morphological observations. The survivalembryos were then tested and investigated to find the degree for their being affected.After the exposure, CAP was found decreased by7%at1.25g/L and14%at1.5g/L,ETM showed no significant effect on the percent of survival, and0.5g/L TC led tothe death of all embryos. CAP and ETM reduced the whole body length by7%and9%at1.5g/L, and0.25g/L TC decreased the whole body length by4%. The multiplemalformations of the embryos that antibiotics may lead to include pericardial edema,enlarged proctodaeums, extended anal, small eyes and bent tails. The percentage oftotal malformation and pericardial edema proves to be44%and34%in1.5g/L CAP treatment group, whereas the percent of total malformation and enlargedproctodaeums turned to be22%and20%in1.5g/L ETM treatment group. What ismore serious, the percent of total malformation and extended anal can be as high as79%and59%in0.25g/L TC treatment group.72h-LC50and EC50for CAP and ETMwere higher than1g/L, and TC was371.2and122.2mg/L. Therefore, TC proves tobe the highest toxicity to Xenopus tropicalis embryos, followed by CAP and ETM.Our results indicate that the antibiotics have potential hazards to the amphibians dueto the increased use of antibiotics in the aquatic environments in recent years.Chronic test, the larvaes of Xenopus tropicalis were exposured from with thestage NF45-46to1~100mg/L CAP, ETM and TC for14d. Observing the cumulativemortality, the overall changes in biomass and developmental stages. The experimentalresults show that the three antibiotics Xenopus tropicalis tadpoles14d LC50of290,253and36mg/L. The cumulative mortality of CAP and ETM at maximumconcentration of100mg/L was21.7%and33.3%, respectively, in TC100mg/L thetadpoles were all nearly death. In CAP treatment groups, the whole body lengthdecreased by10.6%at100mg/L, ETM and TC was decreased by15.7-19.2%and8-22.8%, respectively. The biomass was reduced by16.9-33.2%in CAP treatmentgroups, ETM was reduced by10.7-15.4%, and TC has significantly decreased by17.8-67.1%. About1-2developmental stages were retarded in CAP treatment groups,and1developmental stage was delayed in both ETM and TC treatment groups. Toxicordered to TC>ETM>CAP. The chronic test with larvae of Xenopus tropicalis wasmuch more sensitive than the acute test with embryos following exposure to theselected antibiotics.Joint test, the embryos of Xenopus tropicalis were exposured from the stage NF11-12to0.5-5mg/L CAP,1-10mg/L ETM and0.1-2mg/L TC with0.4mg/L copper,respectively. The experimental results show that compared to0.4mg/L Cu2+alonegroups, in CAP and TC mixture the percentage of survival (POS) were increased by10.9-26.3%and12.5-45%, respectively. The whole body length was also increased by14.6-23.8%in CAP treatment groups and5.4-32%in TC treatment groups. Multiplemalformations such as bent tail, pericardial edema, and enlarged proctodaeum weredecreased in CAP and TC treatment groups. The percentage of teratogenesis (POT)was significantly decreased by13.9-67.5%and8.5-75.6%in CAP and TC treatmentgroups, respectively, but it was no significant effects in ETM treatment groups. CAPwas played an antagonistic role of this exposure but less degree than TC. But ETM was no effects on this.Finally, we review literatures on Pharmaceutical and Personal Care Products(PPCPs)’s environmental analysis and ecotoxicology data, combined with exposureexperiments on Xenopus tropicalis embryos, and conduct ecological risk assessmentanalysis. The results indicate that Xenopus tropicalis embryo as a model organism issuitable for evaluating the risk of antibiotics and other drugs in aquatic environment.