Effects Of Polystyrene Microplastics On The Absorption And Accumulation Of Ciprofloxacin And Its Toxicity In Gramineae

ABSRTACT: Due to the extensive use of plastic products,the public began to pay widespread attention to "white pollution".Plastic waste is gradually broken into microplastics（MPs）which particle size is less than 5 mm in the environment.MPs as a vector for other pollutants,affecting the absorption and biological effects of other pollutants in organisms.Antibiotics（ATs）residues are often detected in water and soil.Researchers have studied the sorption of ATs by MPs in water and soil.The influence of microplastics on the uptake,depuration and toxicity of ATs in organisms has also been studied.However,the effects of MPs on the bioavailability of ATs by gramineae is not well understood.There are few reports on the ecological effects of MPs-ATs contaminant on gramineae and soil microorganisms.In this study,gramineae were selected as experimental subjects.Then polystyrene（PS）and ciprofloxacin（CIP）selected as representative pollutants for experiments.The objectives of the present study were to explore:1.The effects of microplastics on the removal efficiency of antibiotics from ryegrass,the physiological toxicity of MPs-ATs contamination on plants,and the effects of microplastics on the accumulation and removal of ciprofloxacin in ryegrass from water were explored through hydroponic ryegrass.The results of hydroponic experiments indicate that ryegrass could uptake CIP from hydroponic solution with and without MPs.MPs could enhance root uptake of CIP at 0.1 mg/L（100%）,while there was no significant difference in the uptake of 1 mg/L and 2 mg/L CIP with or without MPs（P>0.05）.MPs also increased the translocation of CIP from roots to leaves.Compared to CIP treatment alone,the CIP contents in roots treated with 50.0 mg/L MPs-0.1 mg/L CIP and 50.0 mg/L MPs-2.0 mg/L CIP decreased by 44.0% and 21.2%,respectively.However,CIP contents in leaves increased by 2.9 times and 3.0 times,respectively（P<0.05）.Furthermore,MPs significantly increased the toxic effects of CIP to ryegrass root/leaf elongation and chlorophyll contents.Compared to 2.0 mg/L CIP treatment alone,50.0 mg/L MPs-2.0 mg/L CIP treatment resulted in inhibition of root length and weight by 53.7% and 79.6%,respectively,while the contents of chlorophyll a and chlorophyll decreased by 38.5% and 44.4%,respectively.2.Hydroponic ryegrass at different pH（5.3,7.0 and 8.8）,the changes of microplastic surface groups at different p H（5.3,7.0 and 8.8）were studied,and discussed the phytotoxic effect of PS-CIP contamination at different p H was discussed.The main conclusions are as follow: CIP adsorbed on PS surface were characterized by Fourier transform infrared（FTIR）and the changes of oxygen-containing functional groups on the surface of PS were characterized by X-ray photoelectron spectroscopy（XPS）.In the hydroponic experiment,we investigated the microplastics were obviously aged and the increasement of the oxygen-containing functional groups on the surface of PS.There were hydrogen bonds and π-π* bonds between PS and CIP.p H can affect the adsorption of PS to CIP,which further affects the phytotoxicity of PS-CIP contamination.Compared with CIP treatment group,the leaf length of the 500 nm PSCIP treatment group decreased 9.8%,2.7% and 47.2% at p H 5.3,7.0 and 8.8,respectively.PS-CIP contaminant in water at p H 5.3 and 8.8 is not conducive to the growth of ryegrass.However,all treatment groups had no significant effect on ryegrass leaves.3.Low concentration（0.1%）of 0.45 mm foam and 10 μm PS were co-exposed with ciprofloxacin to cultivate rice seedlings in soil,respectively.Analyzed the effects of PS-CIP contamination on soil physicochemical properties（p H and cation exchange capacity）,soil enzyme activity（fluorescein diacetate hydrolase and urease）and soil microbial communities.In this research,CIP,0.45 mm foam,10 μm PS,0.45 mm foamCIP,and 10 μm PS-CIP contaminants had no significant effect on soil p H at short-term（16 d）cultivation.However,10 μm PS-CIP contamination significantly reduced soil cation exchange capacity（CEC）.Compared with CIP treatment group,0.45 mm PSCIP and 10 μm PS-CIP contaminants increased the activity of fluorescein diacetate（FDA）hydrolase.The soil environment is complex,and many changes are difficult to detect.Through 16 S r DNA,this study found that each treatment group had no significant effect on soil microbial composition and biodiversity,but 0.45 mm PS-CIP and 10 μm PS-CIP enhanced nitrate reduction,nitrate respiration and nitrogen respiration function-related microorganisms microbial communities associated with chemoheterotrophic,oxidative heterotrophic,nitrogen fixation and urea decomposition functions.