Aquatic Toxicity And Selective Adsorption Removal Of Antibiotic And Metal Complex

The co-exsistence of antibiotics and metals prevails in the environment. As is known, antibiotics are rich in various electron donor groups, which can complex with metals. This interaction probably changes the environmental fate and eco-toxicity of antibiotics. However, the previous studies often ignore the complexation when evaluating the combined toxicity of antibiotics and metals, thus leading to an unreasonable estimation of their ecological risks. Moreover, multiple forms of antibiotics present within the environmental relavent pH conditions, the protonated, ionized and metal complexed, which makes pollution control of them complicated. Therefore, it is urgent to assess the combined toxicity of antibiotics and metals and employ proper materials to remove them from water.In this study, two standard toxicity assays, Vibrio fischeri luminescence inhibition test and Scenedesmus obliquus growth inhibition test, were conducted to assess the combined toxicity of two antibiotics (i.e.,ciprofloxacin, CIP and oxytetracycline, OTC) and three metals (i.e., copper, zinc and cadmium), and cyclodextrin polymers (CDPs) were utilized to remove OTC and the mixtures from aqueous systems. The adsorption mechanisms were also explored to provide theoretical evidences for the following screening and designing materials to remove IOCs and their metal complexes.First, with the aid of spectrophotometry, the complexation ratios of CIP with three metals (Cu2+, Zn2+, Cd2+) were determined as1:1or2:1, while OTC formed multiple ratios with metals(1:2,1:1and2:1). Their combined toxicities were evaluated by Vibrio fischeri and Scenedesmus obliquus standardized tests. When ignoring the complexation, combined toxicity varied with the test species and combined ratios of antibiotic and metal, including synergism, antagonism and partial addition. However, additive action was observed for the combined toxicity of antibiotic, metal and the complex, when taking into considerion of complexation between antibiotic and metal. And the most toxic compound was the complex which contributed most to the toxicity of the mixture. Thus, the combined toxicity will be misunderstood if the interaction between antibiotic and metal is ignored.Next, inclusion capacities of CD with OTC under different pH conditions were determined with the help of UV-Vis spectrophotometer. And the inclusion constants of OTC species with CD were calculated via Lingo9.0optimation software. The FTIR and NMR characterization of the prepared inclusion compound demonstrated the dimethylamine group in the OTC molecule was entrapped by CD cavity. And the main driving forces were inferred as hydrogen-bonding, electrostatic and hydrophobic interactions. Moreover, the batch equilibrium method was applied to study the adsorption of OTC by CDPs at varied pH values. Resluts showed that the polymers were evidenced to selectively bind the species and the distribution of the species in the solution remained at the same pH, thus leading to the difference between species-specific and apparent adsorption. Integration of multiple linear regression analysis of adsorption of OTC with CDPs properties and recognition of adsorption mechanisms of the species provided dimension to probing the nature of pH-dependent adsorption of OTC, mainly invoving pore-filling, CD inclusion and network capture.Finally, γ-HP-CDP was screened based on the pH-dependent adsorption nature to remove OTC from simulated wastewater (pH=5,20mg/L) and natural water (pH=7,10μg/L) systems, respectively, with the advantage of high adsorption capacities (over70%) over other CDPs and good regeneration. Besides, environmental levels of cations (Ca24, Mg2+) and humic acid showed no effects on adsorption capacity of γ-MP-CDP. The screened β-γ-CDP was proved with higher affinity (>2times) to the mixture of OTC and Cu in the ratio of2:3and1:2than other mixed ratios, which could be attributed to the increased inclusion capacity of CD with OTC in the presence of metal, but not the different adsorption sites of OTC and metal. These results indicated β-γ-CDP was capable of selective adsorption of the mixtures.