br Materials and method br Results

Materials and method
Results and discussion
Conclusion The adsorption behaviors of 5 antibiotics on 5 types of microplastic particles were investigated using batch type experiments. Our results showed that adsorption capacities varied among antibiotics, plastic types, and environmental conditions (e.g., ionic strength and pH). PA had high affinity for AMX, TC, and CIP in the freshwater system, potentially due to the formation of hydrogen bonding. Adsorption capacities of CIP in the freshwater system were relatively strong related to its cation speciation. All the tested antibiotics exhibited higher amount of adsorption in the freshwater than in seawater. Hydrogen bonding, hydrophobic interaction, van der Waals force, and electrostatic interaction were the main binding mechanisms between antibiotics and MPs. In the future studies, experiments should be performed 1) to investigate adsorption capacities of different speciation of antibiotics (i.e. cation, zwitterion, and anion) on MPs under different pH; 2) to reveal the effects of the major ions (e.g. Cl−, SO3- 4, PO3- 4, Na+) on antibiotics adsorption on MPs; 3) to evaluate the release of adsorbed antibiotics from MPs during their transport from river to ocean.
Acknowledgements This study was financially supported by National Key R & D projects (2016YFC1402202) and the Key projects of international cooperation of Chinese Academy of Sciences (KYSB20160003).
Introduction Antibiotics are routinely used in human and veterinary medicine for the therapeutic treatment of infectious diseases, as well as for animal growth promoters (Kümmerer, 2009a; Zhu et al., 2013). However, antibiotics are excreted as the parent compounds or metabolites due to poor gut AV-951 or incomplete metabolism (Q. Chen et al., 2017, Y. Chen et al., 2017), resulting in frequent detection in aquatic environment due to incomplete removal of antibiotics during wastewater treatment and their continued release into the environment (Hirsch et al., 1999; Kümmerer, 2009b; Ma et al., 2016). The consumption and production of antibiotics in China are the highest in the world (Xin, 2014). The prescriptions including antibiotics account for 70%, while the proportion is only about 30% in western countries, and annual per-capita consumption reaching 138g are approximately 2 times those of the Europe and 10 times those of the United States (Richardson et al., 2005; Yang et al., 2012; Kan et al., 2015). The production of antibiotics in 2013 was up to 2.48×105t which had almost tripled since 2009, and the usage of antibiotics in 2013 is up to 1.62×105t with antibiotics of 5.0×104t/yr into water and soil environment (Zhang et al., 2015). Therefore, the concentrations and detection frequencies of antibiotics in aquatic environment in China are higher than that of some western countries (Qiao et al., 2017). Antibiotics could lead to a selective pressure on the water bacteria and induce the formation of antibiotic resistant bacteria, reducing their therapeutic potential against human and animal pathogens (Carvalho and Santos, 2016; Qiao et al., 2017). Therefore, the antibiotic residues in aquatic environment could pose a potential threat to environment and human health. Lakes, which are important freshwater resources and for flood regulation, are closely related to human production and life (Feng et al., 2012; Chen et al., 2014). China is a country with many lakes, and preliminary statistics show that China has approximately 2800 lakes with an area larger than 1km2 (Le et al., 2010, G. Yang et al., 2010, J.F. Yang et al., 2010). The freshwater resources amount to 2.3×1011m3 (Lu et al., 2017). Approximately 50% of urban drinking water sources, almost 1/3 of national grain output and over 30% of the total output value of industry and agriculture are from lake basins (Leng et al., 2003), However, rapid development has greatly expanded the industry, agriculture and aquaculture of lake basins, which inevitably causes a large number of antibiotics to be used. Zhang et al. (2015) found that the emissions of antibiotics (2190–3560tyr−1) in the Dongting Lake basin were the highest in China. However, the occurrence and environmental risk of antibiotics in the lakes of China are not clear.