Antibiotic contamination in the environment has become a global issue attracting substantial attention from the general public. Intake of antibiotics from the environment by food and drinking water may disturb the microbiome, especially the gut microbiota in the human body (1). More importantly, antibiotic residues in the environment have the potential to produce antibiotic-resistant bacteria (ARB), which pose serious public health risks (2). Antibiotics in aquatic environments and drinking water have been detected in China (3), but studies measuring exposure to antibiotics in drinking water and associated health risks are limited. In this study, contamination levels of antibiotics in raw, finished, and tap water were investigated systematically for the first time in major Chinese water basins during the winter and summer of 2017. Human exposure and its health risks were also evaluated. Study results indicated that multiple antibiotics were generally detected in raw water from major Chinese water basins. Concentrations of detected antibiotics were at the nanogram per liter level, which were similar to those in other developed countries (3). Based on toxicity data or data on therapeutic approaches in the literature, health risk quotients (HRQs) for water basins from exposure to antibiotics via drinking water ranged from 5.1×10−7 to 2.2×10−3, exhibiting spatial and seasonal variations. The HRQs quantified in this study were at an acceptable risk level (HRQs were much lower than 1), but the risks from antibiotic resistance are not well understood and should be researched further. Antibiotic contaminations in environments can induce environmental antibiotic-resistant bacteria (eARB) and horizontal gene transfer (HGT) between eARB and pathogens with antibiotic-resistance (pARB), which has been identified as a major threat to public health. A multisectoral action plan at the national level is required to curb the effects of environmental antibiotic pollution.
Contamination data on antibiotics were extracted from a project investigating emerging contaminants in drinking water in major Chinese river basins. In the project, the levels of contamination of 57 pharmaceuticals in raw, finished, and tap water from representative drinking water treatment plants (DWTPs) located in six large river basins, inland river areas, and key lake and reservoir areas of China during the winter and summer of 2017 were investigated. The water basins and areas investigated in the project included the Yangtze River, Yellow River, Pearl River, Songhua River, Huaihe River, Liaohe River, Northwest Rivers, Taihu Lake, Dianchi Lake, Chaohu Lake, Three Gorges Reservoir, and Danjiangkou Reservoir. Pharmaceuticals were analyzed by an ultra-performance liquid chromatography–tandem mass spectrometer (UPLC–MS/MS), as described in detail in a previous study (3). Based on a literature review and preliminary survey results, 21 antibiotics (Table 1) commonly used for human and animals were selected for analysis in this study. Removal rates (percent eliminated) of antibiotics in DWTPs were calculated by dividing the removal concentration by the concentration in raw water, and the removal concentration was obtained through subtracting finished water concentration from raw water concentration①.
Sub-category Antibiotic Usage* Detection rate in winter(n=54) Concentration in winter Detection rate in summer(n=54) Concentration in summer Percentage (%) Median (P25, P75) (ng/L) Percentage (%) Median (P25, P75) (ng/L) β-lactams (βLs) Penicillin G 1 0 (0/54) ND 0 (0/54) ND Cloxacillin 1 1.9 (1/54) 11.0 1.9 (1/54) 1.2 Cephalecxin 1 38.9 (21/54) 5.1 (2.1, 9.9) 9.3 (5/54) 0.6 (0.5, 0.8) Ceftiofur 2 0 (0/54) ND 0 (0/54) ND Macrolides (MLs) Clarithromycin 1 13.0 (7/54) 1.1 (1.0, 1.5) 68.5 (37/54) 0.3 (0.2, 0.6) Roxithromycin 1 77.8 (42/54) 1.0 (0.7,1.8) 83.3 (45/54) 0.8 (0.4, 1.7) Tylosin 2 3.7 (2/54) 2.8 (2.7, 2.9) 11.1 (6/54) 10.0 (2.7, 83.0) Sulfonamides (SAs) Sulfapyridine 2 33.3 (18/54) 0.8 (0.6, 1.1) 57.4 (31/54) 0.2 (0.1, 0.4) Sulfadiazine 1 50.0 (27/54) 2.5 (1.6, 3.2) 88.9 (48/54) 0.7 (0.2, 1.6) Sulfamethoxazole 1 88.9 (48/54) 9.1 (6.3, 14.0) 90.7 (49/54) 2.4 (1.5, 4.2) Sulfathiazole 1 1.9 (1/54) 98.0 37.0 (20/54) 0.1 (0.1, 0.4) Sulfamethazine 1 46.3 (25/54) 2.2 (1.8, 11.0) 53.7 (29/54) 1.0 (0.4, 2.6) Sulfaquinoxaline 2 7.4 (4/54) 1.1 (0.8, 1.3) 18.5 (10/54) 0.2 (0.1, 0.4) Sulfadoxin 2 0 (0/54) ND 24.1 (13/54) 0.1 (0.1,0.2) Trimethoprim 1 27.8 (15/54) 2.5 (1.9, 2.7) 48.1 (26/54) 0.7 (0.4, 1.0) Quinolones (QNs) Norfloxacin 1 0 (0/54) ND 0 (0/54) ND Ciprofloxacin 1 0 (0/54) ND 14.8 (8/54) 1.8 (0.8, 2.9) Enrofloxacin 2 0 (0/54) ND 20.4 (11/54) 1.4 (0.9, 7.5) Ofloxacin 1 0 (0/54) ND 5.6 (3/54) 1.3 (1.2, 29.0) Clinafloxacin 2 0 (0/54) ND 0 (0/54) ND Sarafloxacin 2 1.9 (1/54) 1.9 59.3 (32/54) 0.4 (0.2, 0.7) The number of detected antibiotics 13 17 * 1=Use for both human and animals; 2=Use for animals only.
Abbreviation: ND=not detected.
Table 1. Detection rates and concentrations of antibiotics in raw water from major Chinese water basins during the winter and the summer of 2017.
The HRQ for each water basin was the sum of the HRQs for each antibiotic detected in tap water. An HRQ for each antibiotic was calculated by dividing its average daily potential dose (ADD) by the acceptable daily intake (ADI) or risk-specific dose (RSD)②. The ADI or RSD for each antibiotic was obtained from literature research. When there were more than one ADIs or RSDs for each antibiotic, HRQs were calculated using the most restrictive ADI or RSD (4). ADD was the antibiotic exposure dose ingested through drinking and dermal absorption during water consumption, calculated with exposure parameters according to Chinese Exposure Factor Handbook and the concentrations of antibiotics in tap water. HRQ above 1 is interpreted as indicating the potential for adverse effects, while HRQ below 1 is interpreted as indicating acceptable risk.
Multiple antibiotics were generally detected in raw water from major Chinese water basins (Table 1), and the detection of antibiotics exhibited seasonal variation. The composition of antibiotic contamination in raw water during the summer was more complex than that during the winter. A total of 17 antibiotics were detected in raw water during the summer with median detected concentrations ranging from 0.1 ng/L to 10.0 ng/L. Among which, seven antibiotics had detection rates above 50%, with 2 of these used for animals only, and the others used for both humans and animals. A total of 13 antibiotics were detected in raw water during the winter, and only two antibiotics detected had detection rates above 50%.
The removal efficiency of each antibiotic from DWTPs was shown in Figure 1. A total of 17 antibiotics detected in raw water had average removal rates of above 50%. β-lactams had average removal rates above 98% and were rarely detected in finished and tap water. Although macrolides (MLs), sulfonamides (SAs), and quinolones (QNs) had average removal rates of 51%–97%, incomplete removal of these antibiotics by conventional technologies in drinking-water treatment plants leaves antibiotic residues in finished and tap water. A total of 16 antibiotics were detected in finished water, and similar results were observed in tap water.Figure 1. Removal efficiency of 17 antibiotics detected in raw water with positive removal rates in the DWTPs. Removal rates (% elimination) were calculated by dividing the removal concentration by the concentration in raw water, and the removal concentration was obtained through subtracting finished water concentration from raw water concentration.
HRQs for water basins ranged from 4.79×10−6 to 2.15×10−3 in the summer and from 5.10×10−7 to 1.69×10−3 in the winter (Table 2). HRQs of human exposure to antibiotics through drinking water exhibited spatial and seasonal variations. Huaihe River and Chaohu Lake basins had HRQs above 10−3 during the summer and the main antibiotic residues in drinking water in these areas were ciprofloxacin and sarafloxacin. Songhua River Basin had HRQs above 10−3 during the winter and the main antibiotic residues in drinking water were clarithromycin and roxithromycin. Additionally, among six large Chinese water basins investigated, the contamination risks in the Yangtze River and Yellow River basins were mainly from sarafloxacin and clarithromycin. The contamination risk in the Pearl River Basin was mainly attributable to tylosin.
Water Basins Season Health risk quotient Minimum Median Maximum Yangtze River (n=10) Winter 8.62×10−6 1.89×10−5 2.57×10−5 Summer 3.71×10−5 4.19×10−5 1.04×10−4 Yellow River (n=10) Winter 2.33×10−5 4.23×10−5 4.40×10−5 Summer 7.17×10−5 1.52×10−4 9.67×10−4 Pearl River (n=10) Winter 5.10×10−7 1.33×10−6 1.73×10−6 Summer 3.33×10−4 5.31×10−4 7.67×10−4 Songhua River (n=10) Winter 9.63×10−5 8.75×10−4 1.69×10−3 Summer 3.67×10−5 3.08×10−4 3.64×10−4 Huaihe River (n=10) Winter 7.48×10−5 2.83×10−4 3.96×10−4 Summer 1.09×10−3 1.81×10−3 2.15×10−3 Liaohe River (n=10) Winter 2.83×10−5 3.01×10−5 6.35×10−5 Summer 1.16×10−4 1.52×10−4 1.80×10−4 Northwest Rivers (n=2) Winter ND* ND* ND* Summer 4.79×10−6 4.79×10−6 4.79×10−6 Taihu Lake (n=10) Winter 1.51×10−5 5.73×10−5 1.23×10−4 Summer 4.40×10−5 7.86×10−5 8.22×10−5 Dianchi Lake (n=10) Winter 2.03×10−5 2.86×10−5 3.00×10−5 Summer 3.35×10−5 7.16×10−5 3.73×10−4 Chaohu Lake (n=10) Winter 3.74×10−5 6.27×10−5 8.02×10−5 Summer 2.95×10−4 1.40×10−3 1.44×10−3 Three Gorges Reservoir (n=10) winter 3.71×10−5 9.59×10−5 1.78×10−4 Summer 1.67×10−5 3.07×10−5 4.20×10−5 Danjiangkou Reservoir (n=8) Winter 3.92×10−5 4.88×10−5 4.92×10−5 Summer 2.32×10−5 1.62×10−4 2.98×10−4 * No antibiotic was detected in drinking water samples from Northwest Rivers Basin area during the winter.
Table 2. Health risk quotients of exposures to antibiotics via drinking water for people from major Chinese water basins during the winter and the summer of 2017.
|①||The formula of removal rate of an antibiotic: Removal rate = (Craw-Cfinished)/Craw×100%, where Craw is the concentration of the antibiotic in raw water (ng/L), Cfinished is the concentration of the antibiotic in finished water in the same DWTP (ng/L).|
HRQs for antibiotic exposure via drinking water were calculated using the concentration of antibiotics in tap water, exposure parameters, and the ADIs or RSDs from literatures. The formulae are presented in the Supplementary Materials available in