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developed and identified quinolones/fluoroquinolones as a group of antimicrobial agents with very high resistance formation potential and very low rates of degradation in the aquatic environment (50 percent after 100 days for fluoroquinolones, compared to 99.8 percent for penicillin after 100 days). 5,6 A separate model revealed the mean predicted concentrations of ciprofloxacin were 579 mg/ m 3 — equivalent (579) in micrograms (μg)/L — in hospital effluent, compared with 0.15 mg/m 3 in seawater receiving effluent from a wastewater treatment plant (WWTP). Based on these predicted concentrations, it is highly unlikely that a swimmer in receiving waters would be exposed to levels of these antimicrobial agents that exceed the acceptable daily intake of 12 μg per kilogram of body weight (kg BW)/day. 5,7 Rodriguez-Mozaz et al. (2015) recently reported detection of fluoroquinolones at a concentration of 4.7 + 0.1 nanograms (ng)/L upstream of a wastewater treatment plant. 8 The presence of antimicrobial residues in the environment can be difficult to detect due to their low concentration, but this doesn't mean they are not having an adverse impact on microbial biodiversity, and potentially on human health, through resistance formation. Currently, environmental quality standards for pollutants are determined based on their direct toxicity or other effects on representative organisms. For antimicrobial agents, it would be prudent to also consider their resistance formation potential. Antibiotic-Resistant Bacteria And Wastewater Patients in major hospitals and residents of long-term care facilities use large amounts of antimicrobial agents and consequently may have antibiotic-resistant bacteria resident in their gut, large numbers of which are passed into the toilet every day. 9 E. coli is a very common gut bacteria and a very common cause of infection (common infections such as urinary tract infection and life-threatening infections such as blood stream infection) and has become increasingly resistant to antibiotics in recent decades. In most European countries, urban wastewater is treated in WWTPs before discharge to the environment. The value of wastewater treatment in reducing antimicrobial-resistant bacteria numbers has been examined in a number of studies. Some researchers report that wastewater treatment helps to reduce the proportion of antimicrobial-resistant bacteria, while others suggest that the treatment process may increase the proportion. The differences in the findings may be because WWTPs differ in the effluent they receive and in the treatment wateronline.com n Water Innovations 9 EMERGINGCONTAMINANTS