br Conclusion br Acknowledgments and disclosure

Conclusion
Acknowledgments and disclosure We thank Ms. Crystal Wylie for her help in the preparation of the manuscript. The development of the database upon which analyses of this study were dependent was supported by PO1 DC 00161 from the National Institute on Deafness and Other Communication Disorders. RLD is President and major shareholder of Sensonics International, the manufacturer and distributor of taste and smell tests, including the commercial version of the University of Pennsylvania Smell Identification Test. He receives funding from the Michael J. Fox Foundation Grant ID# 11805 for Parkinson's Research and royalties from Cambridge University Press, Johns Hopkins University Press, and John Wiley & Sons. He is a consultant to Acorda Therapeutics, Eisai Co., Ltd., Pfizer, and Johnson & Johnson.
Introduction The discovery of penicillin by Sir Alexander Fleming in 1928 opened the modern era of antibiotic innovation and development (Fleming, 1929). Today, PF-9184 are not only used as medicine for humans but are also widely used in animal husbandry and aquaculture. However, antibiotics that are unintentionally discharged into the environment pose a great threat to ecosystems and human health. These antibiotics can accumulate in food webs and, even more alarming, antibiotic resistance genes (ARGs) can be transferred between environmental bacteria and human pathogens (Bengtsson-Palme and Larsson, 2015; Du and Liu, 2012; Li et al., 2015; Martinez et al., 2015; Van Boeckel et al., 2015). Antibiotic resistance is not a new phenomenon (D'Costa et al., 2011; Wright and Poinar, 2012), but the rapid and widespread increase of ARGs has been accelerated in recent years with the increase in discharge of antibiotics and other pollutants (e.g., heavy metals) into the environment (Bengtsson-Palme et al., 2014; Czekalski et al., 2014; Yang et al., 2017b; Yin et al., 2013). In fact, ARGs have recently been regarded as an emerging pollutant (Pruden et al., 2006). As such, antibiotics and their effects on the environment (ARGs, antibiotic resistant bacteria (ARB), etc.) have become an important theme in environmental science. Aquatic environments are major pools for antibiotics and ARGs. Effluents from wastewater treatment plants, industry, hospitals and pig farms, for example, will all eventually reach some water source (Lavilla Lerma et al., 2014; Liu et al., 2012; W. Zhang et al., 2009; Zhu et al., 2013). The effects of antibiotics on aquatic micro-organisms, the nitrogen cycle and natural ecosystems have been summarized (Grenni et al., 2018; Roose-Amsaleg and Laverman, 2016; Välitalo et al., 2017). The distribution and environmental behaviour (e.g., adsorption and degradation) of antibiotics in aquatic environments have also been reviewed (Bu et al., 2013; Kümmerer, 2009a, Kümmerer, 2009b; Liu and Wong, 2013). However, some aquatic environments, specifically lakes and rivers, behave differently due to their different hydraulic characteristics. In rivers, the concentration of pollutants in sediments gradually decreases downstream of a source due to hydraulic characteristics (Pruden et al., 2012; Reuther, 2009). Rivers seem to have received most attention among aquatic environments, likely due to their rapid transport of antibiotics and ARGs and the obvious identification of pollution sources and landscapes in different reaches (Chen et al., 2013; Pruden et al., 2012; Rodriguez-Mozaz et al., 2015; Storteboom et al., 2010). In lakes, the residence time of contaminants increases because of the long water retention time relative to rivers. This means that pollutants from discharges slowly circulate around the lakes and makes pollution control in lake basins especially critical (Lyandres, 2012; Reuther, 2009). Due to these characteristics, lakes are predicted to have the potential to store and accumulate ARGs to a greater extent than rivers (Czekalski et al., 2015). Lakes serve as an important drinking source of freshwater, containing nearly 90% of the liquid surface fresh water worldwide; in contrast, rivers contain only 2% (McConnell and Abel, 2013).