Distribution, dynamics and determinants of antibiotics in soils in a peri-urban area of Yangtze River Delta, Eastern China

Chemosphere 211 (2018) 261e270

Contents lists available at ScienceDirect

Chemosphere journal homepage: www.elsevier.com/locate/chemosphere

Distribution, dynamics and determinants of antibiotics in soils in a peri-urban area of Yangtze River Delta, Eastern China Fangkai Zhao a, b, Liding Chen a, b, Lei Yang a, b, *, Shoujuan Li a, b, Long Sun a, Xinwei Yu c a

State Key Laboratory of Urban and Regional Ecology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China University of Chinese Academy of Sciences, Beijing 100049, China c Key Laboratory of Health Risk Factors for Seafood of Zhejiang Province, Zhoushan Municipal Center for Disease Control and Prevention, Zhoushan 316021, China b

h i g h l i g h t s

g r a p h i c a l a b s t r a c t


Antibiotics in soils were investigated in a typical peri-urban catchment of Yangtze River Delta, China.
Antibiotic concentrations (i.e. chlortetracycline) in cropland soils were higher than those in orchard and forest.
Land use intensity and structure significantly correlated with antibiotic concentrations (p < 0.05).
Anthropogenic factors contributed more to soilcontamination by antibiotics.

a r t i c l e i n f o

a b s t r a c t

Article history: Received 4 March 2018 Received in revised form 22 July 2018 Accepted 27 July 2018 Available online 30 July 2018

Antibiotics are increasingly recognized as anthropogenic contaminants in soils, and they can persist through a complex vicious cycle of transformation and bioaccumulation. In this study, we quantified 11 quinolones (QNs), 5 sulfonamides (SAs), 5 macrolides (MLs), and 4 tetracyclines (TCs) in soils at three soil layers (0e10, 10e20, 20e40 cm) in a typical peri-urban catchment in the Yangtze River Delta, Eastern China. The results showed that total antibiotic levels were significantly higher in cropland topsoil (p < 0.05) compared to orchards and forests (p < 0.05). Moreover, a significant seasonal variation for antibiotic concentrations in croplands’ topsoil were observed in the summer (50.59 ± 84.55 ng/g) and winter (112.44 ± 140.58 ng/g). Chlortetracycline (15.30 ± 45.44 ng/g), enrofloxacin (0.43 ± 0.93 ng/g), sulfamethazine (0.05 ± 0.02 ng/g) and clarithromycin (0.03 ± 0.03 ng/g) were detected with the highest frequencies within TCs, QNs, SAs, and MLs, respectively. Concentrations of TCs, QNs, and SAs decreased with increasing soil depth. The concentrations of TCs, QNs, and SAs were significantly affected by the intensity of human activities. According to the results of redundancy analysis (RDA), anthropogenic effects on the distribution of antibiotics in soils in winter were so strong that they dwarfed the effects of environmental factors. In summer, human activities and their interactions with environmental factors were the dominant contributors to variations in soil antibiotics. In addition, the results of RDA suggested that soil pH and organic matter closely correlated with the levels of antibiotics, and Actinobacteria was the predominant contributor to the biodegradation of antibiotics in this study area. © 2018 Elsevier Ltd. All rights reserved.

Handling Editor: Klaus Kümmerer Keywords: Antibiotics Land use Seasonal variation Spatial distribution

* Corresponding author. Shuangqing Road 18, Haidian District, Beijing 100085, China. E-mail address: [email protected] (L. Yang). https://doi.org/10.1016/j.chemosphere.2018.07.162 0045-6535/© 2018 Elsevier Ltd. All rights reserved.

262

F. Zhao et al. / Chemosphere 211 (2018) 261e270

1. Introduction Antibiotics are commonly and widely used for human health and animal growth (Kümmerer, 2009a, 2009b; Tasho and Cho, 2016). Between 2000 and 2010, global consumption of antibiotics increased by 36%, and China is one of the largest producers and consumers of antibiotics with an estimated production of 210,000 t per year (Li et al., 2015; Van Boeckel et al., 2014). Antibiotics cannot be completely adsorbed and metabolized by humans or other animals: approximately 16%e84% of antibiotics are excreted via urine and feces (Awad et al., 2014; Martinez, 2009). There is a concern that environmental input of antibiotics via land application of manure, effluent from municipal wastewater treatment, or irrigation with reclaimed water may increase antibiotic concentrations in the environment (Martinez, 2009). Furthermore, high concentrations of antibiotics in the environment can be associated with an increased presence of resistant bacteria, which is an important public health concern due to the prevalence of associated clinical infections (Zhu et al., 2017). Previous studies have reported high concentrations of antibiotics in agricultural soils due to fertilization and irrigation (Christou et al., 2017; Pan and Chu, 2017a; Wu et al., 2015). For example, Zhang et al. (2015) reported that 53,800 tons of antibiotics were excreted by humans and animals in China, with 54% accumulating in soil compartments. In addition, antibiotics persist in soil environments over the long term with continuous loading of antibiotic pollutants (Rahman et al., 2018; Riaz et al., 2018). Indeed, in a field with a 13-year history of manure application, the mean concentrations of selected antibiotics in soils increased by at least 120% (Li et al., 2017). Residual antibiotics in soils can inhibit the growth of crop roots and soil microorganisms. Meanwhile, they can also lead to abundant antibiotic resistance genes (ARGs) and a diverse array of resistant bacteria, seriously threatening the security and stability of soil ecosystems (Kümmerer, 2009b; Liang et al., 2017; Zhao et al., 2017). Moreover, antibiotic residues in soils due to agricultural practices may represent an enhanced threat to human health via ingestion of contaminated food (Pan and Chu, 2017a; Tasho and Cho, 2016; Wei et al., 2016). Antibiotic compounds have different persistence and transportation modalities and abilities in soils, including sorption, degradation, and leaching (Kümmerer, 2010; Pan and Chu, 2017a). The environmental fate of antibiotics in soils is more likely to be affected by the physicochemical properties of antibiotics (Tolls, 2001). Tetracyclines are associated with several orders of magnitude higher sorption ability than other antibiotics (Rabølle and Spliid, 2000; Kuppusamy et al., 2018). For example, the soil adsorption coefficient (Kd) of sulfachloropyridazine ranges from 0.90 to 1.80 (1/kg) in clay loam, while chlortetracycline exhibits the highest adsorption ability with Kd ranging from 1280 to 2386 (1/kg) (Pan and Chu, 2017a). The sorption, migration, and degradation of antibiotics in soils is significantly affected by soil pH, soil texture, metals ions, organic matter, rainwater pH, and rainfall duration (Pan and Chu, 2017b; Qin et al., 2017; Zhang et al., 2014). For tetracyclines, cation exchange is an important mechanism for their adsorption in clay minerals, which is depended on the charge of both antibiotic compounds and clay minerals (Pils and Laird, 2007). Tetracycline antibiotics are positively charged in strongly acidic solutions indicating neutralize negative charge sites on clay surface, while they are anionic under alkaline conditions which will be repulsed from clay surfaces (Aristilde et al., 2010; Figueroa et al., 2004). Additional, the charge of clays can also vary with pH, and inner-sphere sorption is the main mechanism of adsorption for tetracyclines antibiotics on variable charge clay minerals (Zhao et al., 2011). It was reported that the presence of Ca2þ and Mg2þ can strongly account for the formation of inner-sphere complexes

with tetracycline antibiotics, which can influence antibiotic retention behaviour on mineral surfaces (Aristilde et al., 2016; Dolui et al., 2018). Studies have also found that there are complex relationships between antibiotic concentrations and bacterial communities in soils. Soil bacterial communities are significantly changed under the selection pressures of antibiotics due to the effects of antibiotics on microbial activity and biomass (Hammesfahr et al., 2008; ThieleBruhn and Beck, 2005). Certain bacteria can also degrade antibiotics (Liao et al., 2016a). However, there is a lack of clarity vis-a-vis the differential contribution of anthropogenic and environmental factors on the persistence and distribution of antibiotics in soils. In recent decades, rapid urbanization and agricultural development have greatly affected the soil environment in the Yangtze River Delta (YRD), China. To meet increasing demand for organic produce, long-term and heavy application of animal manures in agricultural fields has occurred, especially in peri-urban areas due to multiple economic and social benefits. However, this cultivation may also elevate the contamination of soils with antibiotics. Most urban wastes subsequently decompose in peri-urban areas, and many ecosystem services are supplied by peri-urban soils such as food supply, soil carbon sequestration, and water conservation. Contamination of soil by antibiotics risks undermining these ecosystem services. Illuminating the spatial and seasonal variation of soil antibiotics in peri-urban areas could promote the sustainability of soil and the delivery of ecosystem services. In a typical peri-urban catchment of YRD, soil antibiotics and determinants thereof were quantified and explored. Specifically, in this study, we aimed to: (1) compare the composition and concentration of soil antibiotics across different land use types; (2) explore the spatial distribution of soil antibiotics and its seasonal variation in periurban areas; (3) identify the main determinants of spatial and temporal variations in soil antibiotics. 2. Materials and methods 2.1. Study area The Zhangxi catchment (29 450 e29 510 N, 121130 e121200 E), located in a rapidly urbanizing area of Yangtze River Delta, Eastern China, was selected as the study area (Fig. 1). The catchment has an area of 91.6 km2 and is located in the typical peri-urban area of Ningbo city. It has a subtropical monsoon climate, with an annual mean cumulative precipitation of 1480 mm. Mean monthly temperature is highest in July (28.0  C) and lowest in January (4.7  C). The soil layer in the catchment is shallow (mean of ca. 30 cm) and is typically characterized by a silt loam topsoil with a sandy loam subsoil. The main land use types in the catchment are forests, cropland, orchards, residential areas, a river, and a reservoir. Cropland (fritillaria, vegetables, fruit) is mainly distributed along the river channel. Organic fertilizer or manure is widely applied to cropland in October of each year; and some orchards are also fertilized in this way. The study area was classified into four sub-catchments (SC1, SC2, SC3, and SC4) with an ‘obvious human activities’ gradient. SC1 is essentially a natural ecosystem, with forest coverage of 96.3%, while there are intensive human activities in SC4 with a high proportion of cropland and villages (35.8% and 10.3%, respectively); see Table S1. 2.2. Soil sampling and characterization A total of 82 sampling sites were selected in the catchment in July 2016 (summer) and January 2017 (winter). The daily average

F. Zhao et al. / Chemosphere 211 (2018) 261e270

263

Fig. 1. Location of the study area and sampling sites.

atmospheric temperature for sampling campaigns was 28.4  C and 7.8  C, respectively. At each experimental site, five to eight points were collected randomly, and all soil samples from each point were fully mixed. Due to the shallow soil layer in the study area, we collected soil samples at the depth of 0e40 cm. According to previous studies, antibiotics showed clear differences in soil column at depth of 0e10 cm, 10e20 cm and deeper soil layer (>20 cm) (Kay et al., 2005). Thus, to evaluate the vertical distribution of antibiotics in field environment, soil samples were collected from three depths in this study. Composite soil samples were cold-stored (20  C) and then sent to the laboratory for analysis. Basic soil physico-chemical properties and bacterial communities in soil samples were measured. Soil pH was determined using an electrode-equipped pH meter with a soil-to-water ratio of 1:2.5. Soil moisture content (SMC) and bulk density (BD) within the topsoil (10 cm) were measured simultaneously for 3 replicates using steel rings (5 cm diameter x 5 cm height) by the oven-dried method. Soil texture was determined by the laser diffraction method using a laser particle analyzer. Available phosphorus (AP) in soil was extracted using 0.5 mol L1 sodium bicarbonate; whilst available potassium (AK) was extracted using ammonium acetate and determined by flame photometry (Zheng et al., 2009). Total carbon (TC) and total nitrogen (TN) in soil were determined using an elemental analyzer. Soil organic carbon (SOC) was determined using the dichromate oxidation method, and soil organic matter (SOM) was calculated from SOC (Zheng et al., 2009). The concentrations of Al, Fe, Cu and Ca in soil were determined by X-ray fluorescence (XRF) spectrometry (McLaren et al., 2012). Bacterial communities were characterized using a 16S rRNA gene sequencing method as described by Zhu et al. (2017). 2.3. Quantifying human activities Accessibility of human activities, measured in terms of distance to road (DR), distance to town (DT), altitude, and intensity of land use, was used to indirectly represent the intensity of human disturbances (Nogues-Bravo et al., 2008). DR and DT were captured from Google Earth, and altitude was determined by GPS at each experimental site. The intensity of land use was characterized by a

landscape development intensity coefficient: cropland ¼ 7, orchards ¼ 3.68, and forests ¼ 1 (Brown and Vivas, 2005). 2.4. Extraction and analysis of antibiotics Four groups of antibiotic compounds were selected based on their frequent occurrence in manure and soils in China, especially in Yangtze River Delta, as well as their environmental behaviour (Wei et al., 2016; Sun et al., 2017; Qiao et al., 2018; Xie et al., 2018). Target antibiotic compounds in this study are showed in Table 1: quinolones (QNs, 11 chemicals); sulfonamides (SAs, 5 chemicals); macrolides (MLs, 5 chemicals); and tetracyclines (TCs, 4 chemicals). The physicochemical properties of the targeted antibiotics are shown in Table S2. Target antibiotic standards were all obtained from Dr Ehrenstorfer (Augsburg, Germany). Individual stock solutions were prepared at 100 mg/L in methanol and stored in an amber glass vials at 20  C in dark. The extraction method was optimized based on Zhou et al. (2017). Freeze-dried soil samples were sieved through a 60-mesh screen; 2.0 g of soil was weighed into 50 mL centrifuge tubes with 7.5 mL of Na2EDTA-McІlvaine buffer (pH ¼ 4.0) and 7.5 mL of methanol-acetonitrile-acetone (v/v/v ¼ 2:2:1). The solution was vortexed for 1 min, ultrasonically extracted for 20 min, and then centrifuged for 5 min at 3000 rpm. This procedure was repeated twice and the supernatants were pooled and diluted to 500 mL. The diluted supernatants were then filtered through a 0.22-mm glass microfiber (GF/F, Whatman, UK) and the pH of the mixture was adjusted to 3.5. The filtrate was applied to Oasis HLB cartridges (6 mL, 200 mg, Waters, Milford, MA, USA) which were preconditioned with 6 mL of methanol, 6 mL of acetone, and 6 mL of 0.5 g/L Na2EDTA solution (pH ¼ 3.5). The loading rate of the mixture was maintained at 5e10 mL/min. After loading, the cartridges were rinsed with 5 mL of ultrapure water and 5 mL of 5% methanol solution, followed by vacuum drying for 20 min. The dried cartridges were eluted by 3 mL of methanol and 5 mL of 1% formic acid in methanol. The eluates were evaporated to approximately 0.1 mL using nitrogen gas, and 1 mL solvent of methanol-water (v/v ¼ 1:1, acidified by 1% formic acid) was added to each sample. The solution was stored at 20  C

264

F. Zhao et al. / Chemosphere 211 (2018) 261e270

Table 1 Antibiotics selected in this study. Groups

QNs

Analytes

Enrofloxacin ENR Ofloxacin OFL Ciprofloxacin CIP Norfloxacin NOR Perfloxacin PER Flumequine FLU

Difloxacin DIF Lomefloxacin LOM Sarafloxacin SARA Danofloxacin DANO Oxolinic acid OXA

prior to high performance liquid chromatography tandem mass spectrometry (HPLCeMS/MS) analysis. The HPLCeMS/MS (Thermo Dionex Ultimate 3000, USA) with C18 columns (Waters Acquity UPLC BEH, 100 mm  2.1 mm, 1.7 mm) was used for analysis of antibiotics. The mobile phase consisted of eluent A (pure water with 0.2% methanol) and eluent B (methanol: acetonitrile ¼ 4:6, v/v). The rates of recovery of the target compounds ranged between 64.5% and 107.6%. The limit of detection (LOD) based on a signal-to-noise ratio of 3 ranged from 0.05 to 2.00 ng/g. Recovery and LOD are depicted in Fig. S1. Eight concentrations (0.2, 0.5, 2, 5, 10, 50, 100, and 300 mg/L) of individual antibiotics were used to construct the calibration curves (R2  0.99). 2.5. Statistical analysis Total antibiotic concentrations were log-transformed, and oneway ANOVA was used to examine differences in total antibiotic concentrations between soils under different land use types. A Kolmogorov-Smirnov non-parametric test was applied to examine differences in individual antibiotics between soils under different land use types. Next, principal component analysis (PCA) was used to identify the vertical and temporal variance among the dominant antibiotics in soils under different land use types. ANOVA and PCA were implemented using SPSS 22. Redundancy analysis (RDA) and variation partitioning analysis (VPA) were then applied to evaluate the effects of soil physico-chemical properties, human activities, and bacterial communities on the distribution of antibiotics in soil. RDA and VPA were implemented using Canoco 5. 3. Results 3.1. Concentration and composition of antibiotics over space and time The range of total antibiotic concentrations across the 82 experimental sites in different land use types is illustrated in Fig. 2. Total antibiotic concentrations in cropland were significantly (p < 0.05) higher than those in orchards and forests, both in summer and winter. There was no significant difference between orchards and forests in summer (p > 0.05). However, in winter, total antibiotic concentrations in the topsoil of orchards were significantly higher than their counterparts in forests (p < 0.05). In addition, significant differences in the total antibiotic concentrations of topsoil in cropland were found between summer and winter, with no such significant differences found in orchards and forests between the two seasons. There was a wider variance range of antibiotics in topsoil from cropland, with higher coefficients of variation (CV, 1.67 in summer and 1.25 in winter) compared to orchards and forests. The variability in total antibiotic concentrations

TCs

SAs

MLs

Chlortetracycline CTC Oyxtetracycline OTC Doxycycline DXC Tetracycline TC

Sulfamethazine SMZ Sulfamethizol STZ Sulfamethoxazole SMX Sulfachloropyridazine SCP Sulfisoxazole SXZ

Clarithromycin CLA Tylosin TYL Erythromycin ERY Roxithromycin ROX Spiramycin SPI

was highest in orchards and lowest in forests, in both summer and winter. Similar CVs were revealed for antibiotics in different soil layers in croplands and orchards, while the CVs in forest topsoils tended to be lower than those calculated with respect to deep soils. In summer, there were higher CVs of total antibiotic concentrations both in cropland and orchards, with higher CVs observed in winter for forests (see Table S3). As shown in Table 2, in the topsoil of croplands, TCs had the highest mean concentrations at 41.43 ng/g in summer and 105.72 ng/g in winter. TCs in orchard topsoils also occurred at high concentrations with mean values of 2.49 ng/g (summer) and 19.35 ng/g (winter). But in forest topsoil, TCs showed the highest mean concentration in winter only, while QNs were dominant in summer with a mean concentration of 0.63 ng/g. In both summer and winter, the concentrations of TCs, QNs, and SAs decreased with increasing soil depth under different land use types, but the concentrations of MLs decreased with increasing soil depth, thus exhibiting a different vertical distribution trend compared with TCs, QNs, and SAs. The results suggest that the vertical distribution and transportation of antibiotics released into the soil environment were likely influenced by similar factors under different land use types. The composition of antibiotics in soils under different land use types across the two seasons is presented in Fig. 3. This shows that TCs and QNs were the two main types of antibiotics found across all land use types in the summer. However, MLs predominated in soils at a depth of 20e40 cm in winter. SAs exhibited the lowest proportions in soils under different land use types in both summer and winter. In summer, the proportion of TCs in topsoil decreased in the order of cropland > orchard > forest, while the proportion of MLs increased in the same order. There were similar trends in the two other soil layers, 10e20 cm and 20e40 cm. However, in winter, TCs were found at relatively high proportions in topsoil. The proportion of TCs decreased with increasing soil depth. The opposite vertical distribution pattern was revealed for MLs in soils. An especially high proportion of QNs was uncovered in orchard soils at a depth of 10e20 cm due to differences in fertilization methods. These results demonstrate impressionable variations in antibiotic concentrations in soils, especially topsoil. At the disaggregated level, the results suggest that two tetracyclines (CTC and DXC) and four quinolones (ENR, OFL, CIP, and NOR) were the most frequently detected antibiotic compounds in peri-urban topsoil. In cropland, ENR had the highest detection frequency (100%) in summer, with OFL showing the highest detection frequency (97.5%) in winter. CTC was the dominant antibiotic pollutant in cropland soil with the highest maximum concentration of 342.73 ng/g in summer and 535.89 ng/g in winter. A Kolmogorov-Smirnov nonparametric test showed that CTC concentrations were significantly higher than DXC, OTC, and TC both in

F. Zhao et al. / Chemosphere 211 (2018) 261e270

265

Fig. 2. Total antibiotic concentrations in soils under different land use types at depths of (a) 0e10 cm, (b) 10e20 cm, and (c) 20e40 cm. Different letters indicate significant differences at the 0.05 level. Horizontal lines demarcate the 5th, 25th, 50th, 75th, and 95th percentiles of distributions. Black points indicate minimum and maximum values.

Table 2 Concentrations of antibiotics in soils in different land uses (ng/g, dw a). Season

Groups

Land use types

summer

TCs QNs SAs MLs TCs QNs SAs MLs

41.43 b/16.36 c/4.40 8.97/5.31/1.11 0.07/0.02/0.01 0.11/0.22/0.35 105.72/13.61/4.02 19.35/4.99/1.86 0.28/0.02/0.02 0.60/0.90/0.95

Cropland

winter

a b c d e

d

Orchard

Forest

2.49/1.34/0.57 1.09/0.23/0.23 0.03/0.01/n.d. e 0.08/0.18/0.21 19.35/0.31/0.13 2.85/0.82/0.53 0.08/n.d./n.d. 0.20/0.22/0.37

0.12/0.31/0.21 0.62/0.18/0.19 0.02/n.d./n.d. 0.13/0.16/0.16 2.93/0.25/0.17 0.64/0.16/0.08 0.06/n.d./n.d. 0.22/0.20/0.38

Dw means dry weight. Mean concentrations of antibiotics in soils at 0e10 cm. Mean concentrations of antibiotics in soils at 10e20 cm. Mean concentrations of antibiotics in soils at 20e40 cm. Not detected.

summer and winter (p < 0.05) in cropland. However, significant differences were not observed among CTC, DXC, OTC, and TC in soils from orchards and forests (p > 0.05). Compared with TCs, QNs were observed at relatively low mean concentrations in soils. Among five frequently detected QNs, OFL was present at relatively high mean concentrations (2.97 ng/g in summer and 6.56 ng/g in winter).

However, there were no significant differences between OFL and NOR and ENR and CIP (p > 0.05), while LOM occurred at significantly lower concentration only in cropland soil (p < 0.05). In forests, MLs were also notable alongside TCs and QNs, contributing 14.58% and 42.54% of total antibiotic concentrations in summer and winter, respectively (Fig. S2). ERY had the highest mean concentrations of 0.12 ng/g and 1.41 ng/g in summer and winter. However, the detection frequencies of ERY were rather low: 27.59% in summer and 26.67% in winter. CLA showed the highest detection frequency of 44.83% in summer and ROX were higher in winter with a frequency of 36.67% in summer. (Tables S4 and S5).

3.2. Spatial and temporal variation of antibiotics in soils The spatial and temporal distribution pattern of total antibiotics are shown in Fig. S3. Overall, across the whole catchment, total antibiotic concentration in soils at different soil layers ranged from 3.584 ± 7.705 ng/g (20e40 cm) to 25.597 ± 63.661 ng/g (0e10 cm) in summer, and 5.876 ± 14.155 ng/g to 56.592 ± 112.044 ng/g in winter. However, the concentrations of antibiotics detected in soils from the four sub-catchments exhibited clear variability (Fig. 3). Total antibiotic concentrations in topsoil of SC1 were particularly low with mean values of 0.584 ± 0.296 ng/g in summer and

Fig. 3. Total antibiotic concentrations in soils from different subcatchments in depths of (a) 0e10 cm, (b) 10e20 cm, and (c) 20e40 cm. The horizontal lines demarcate the 5th, 25th, 50th, 75th, and 95th percentiles of the distributions. The black points indicate the minimum and maximum values.

266

F. Zhao et al. / Chemosphere 211 (2018) 261e270

1.098 ± 1.381 ng/g in winter. Mean values were significantly higher in SC4 compared to the other sub-catchments (59.879 ± 80.315 ng/ g in summer and 189.757 ± 172.687 ng/g in winter). Mean antibiotic concentrations in soils increased from SC1 through SC4. These trends were consistent with land use differences in the 4 subcatchments; the proportion of cropland, villages, and orchards also increased from SC1 through SC4. Mean concentrations of total antibiotics showed similar variation in soils at depths of 10e20 cm and 20e40 cm. However, significant correlations were observed between total antibiotic concentrations and the proportion of cropland area at all soil depths (p < 0.05), except at 20e40 cm in summer due to the lower intensity of human activity (p > 0.05). Positive correlations were also found between total antibiotic concentrations and proportion of land occupied by villages and towns although they were not significant (p > 0.05); see Fig. S4. As shown in Fig. S5, the results of PCA indicate that a broad change occurred in the main antibiotic classes in soils under different land use types from the four sub-catchments between summer and winter. The first components were all heavily weighted by TCs, QNs, and SAs, while the second components were weighted with MLs. Notably, a broader variation in detected antibiotics was observed in cropland soils at different depths. There were significant increasing trends in TCs, QNs, and SAs in topsoil in winter (p < 0.05), while no such significance was revealed in the other soil layers. Compared with these antibiotic compounds, MLs increased markedly from summer to winter in cropland in all soil layers. However, there were less obvious differences in the concentration patterns of detected antibiotics in soils from forests and orchards (p > 0.05), except for MLs in topsoil (p < 0.05). We found higher concentrations of TCs, QNs, and SAs in topsoil, especially in winter. However, this variation was not statistically significant in forests (p > 0.05). These data confirm that levels of antibiotics in soils were determined by land use structures, and agricultural activities were the main sources of TCs, QNs, and SAs. 3.3. Correlations between soil physico-chemical properties, human activities, bacterial communities, and antibiotic concentrations

Table 3 Bivariate Spearman's correlations between human activities and antibiotic concentrations in topsoil in summer. Time

Groups

Distance to road (m)

Distance to town (m)

Altitude (m)

summer

TCs QNs SAs MLs Total TCs QNs SAs MLs Total

0.353** 0.308** 0.255* 0.023 0.338** 0.491** 0.391** 0.467** 0.143 0.484**

0.336** 0.357** 0.351** 0.107 0.327** 0.618** 0.570** 0.408** 0.091 0.629**

0.602** 0.623** 0.402** 0.056 0.640** 0.751** 0.683** 0.558** 0.080 0.800**

winter

*Significant at the 0.05 level. **Significant at the 0.01 level.

cropland, orchard and forest, respectively (p < 0.05). Results also showed that soil Fe content was positively correlated with QNs and MLs in forest soils (p < 0.05). In addition, Cu also showed significant correlations with TCs and QNs antibiotics in soils (p < 0.05). Although the soil bacterial communities obviously changed between summer and winter (Fig. S4), the results of RDA in two seasons both indicated that Actinobacteria was the predominant influencing bacterial species, while the effects of Planctomycetes, Chloroflexi and Gemmatimonadetes were secondary (Fig. 4). In the variation partitioning analysis (Fig. 5), 75.1% of the variance of antibiotics could be explained by selected variables, with 24.9% of the variance unaccounted for. The interaction between human activities and soil physico-chemical properties was the single biggest determinant of variance in soil antibiotics (21.4%). Human activities and soil physico-chemical properties explained similar variation in summer (11.4% and 12.5%, respectively), with bacterial communities lagging behind as a near negligible determinant (0.8%). Over 60% of the observed variation in antibiotics was explained by human activities and their interactions with soil physico-chemical properties and bacterial communities.

4. Discussion Due to enhanced human activities (Table 3) and reduced microbial activities in winter in this study area, there were no significant (p > 0.05) effects of microbial communities and soil physico-chemical properties on the distribution of soil antibiotics according to RDA results (Fig. 4). There were also no significant correlations found between total antibiotic concentrations and soil physicochemical properties at regional scales in the Yangtze River Delta according to the recent study by Sun et al. (2017). Thus, to explore the contribution of different determinants on the distribution of soil antibiotics, we focused on their effects in summer. Moreover, obvious variations in antibiotics mainly occurred in the topsoil of the different land use types. Table 3 shows that concentrations of TCs, QNs, and SAs in topsoil were positively correlated with parameters representing the intensity of human activities. Total antibiotic concentrations also showed a close correlation with human activities (p < 0.05). However, concentrations of MLs in topsoil were not significantly influenced by human activities (p > 0.05). According to redundancy analysis, soil pH, bulk density, available K, and soil texture were the principal factors affecting the spatial distribution of antibiotic concentrations (Fig. 4). However, soil clay content, which was generally recognized as an indicator of antibiotics’ sorption, showed negative correlations with most antibiotics. Although SOM showed weak correlations with antibiotic concentrations in soils across all land use types, Table S6 showed SOM significantly correlated with TCs and QNs in soils within

4.1. Effects of land use on antibiotic distribution in soils The results showed that antibiotics were detected in soils from all land use types, especially in cropland soils (Fig. 2), and TCs and QNs were the main antibiotic types in cropland soils (Fig. S2). Previous studies have documented high levels of antibiotic residues in manures and organic fertilizers due to the overuse of antibiotics on livestock as antibacterial agents and growth promoters (Hou et al., 2015). Therefore, use of manures and organic fertilizers in agriculture can lead to contamination of soil with antibiotics (Wei et al., 2016; Zhang et al., 2016a). Moreover, previous studies have also found that TCs and QNs are prevalent, exhibiting higher concentrations in manures than SAs and MLs (Zhang et al., 2016a). TCs and QNs can be more strongly absorbed by soil particles (Tolls, 2001) and as such are more prone to persist in soils, especially in cropland. Across the Austrian territory, only CTC was detected frequently in agricultural soils, although most selected antibiotic compounds occurred in manures (Martinez-Carballo et al., 2007). A recent regional-scale evaluation of pollution from multiple antibiotics in agricultural soils of the Yangtze River Delta demonstrated that concentrations of TCs and QNs were significantly higher than SAs with mean concentrations of 34.9 ng/g and 48.8 ng/g (Sun et al., 2017). In comparison, total antibiotic pollution levels in our investigated area were lower than those in greenhouse vegetable production systems (28 ng/g to 1058 ng/g) in Beijing, China (Li et al.,

F. Zhao et al. / Chemosphere 211 (2018) 261e270

267

Fig. 4. Redundancy analysis differentiating the effects of soil physico-chemical properties and bacterial communities on the distribution of antibiotics in topsoil. Note: a and b represent the effects of soil physico-chemical properties in summer and winter, respectively; c and d represent the effects of bacterial communities in summer and winter, respectively.

Fig. 5. Variation partitioning analysis differentiating the effects of soil physicochemical properties, human activities, and bacterial communities on the distribution of antibiotics in topsoil in summer.

2015), and vegetable farmland soil in the Pearl River Delta area, Southern China with a mean value of 394.9 ng/g for total antibiotics (Li et al., 2011). In other countries, such as Malaysia and Turkey, relatively high levels of total antibiotics in agricultural soils have been documented (Ho et al., 2014; Karci and Balcioglu, 2009). However, levels were lower in soils from Mount Suswa Conservancy, Kenya (12.21 ng/g) and Pego e Oliva Marshlands, Spain (3.41 ng/g) (Vazquez-Roig et al., 2012; Yang et al., 2016b) where human disturbances were absent. The limited literature currently available on the distribution of antibiotics in soils has tended to focus on agricultural soils; the effects of land uses on the concentration and composition of antibiotics in soils has hitherto been neglected. Our results suggested that antibiotic concentrations in agricultural soils were relatively high due to human activities, and land use types are important determinants of the levels of antibiotics in soils. However, according to our results, MLs were also found in high proportions in forest soils, especially in the deep soil layer (Fig. S2). However, these antibiotics could conceivably accumulate in natural soils due to production by microorganisms (Aminov, 2009). Moreover, they can also be degraded by microbial activities. For example, complete degradation of erythromycin in non-sterilized soil has hitherto been observed under aerobic conditions (Pan and Chu, 2017a). MLs have low partitioning coefficients, suggesting that they are highly mobile in the environment via runoff and soil loss (Tolls, 2001). Thus, MLs, such as erythromycin, could be transported into deeper soil layers and groundwater and pose

268

F. Zhao et al. / Chemosphere 211 (2018) 261e270

higher risks (Pan and Chu, 2017a). Additionally, antibiotics can enter into forest soils via atmospheric particulates and precipitation (Ferrey et al., 2018). However, our results also show that the intensity of human activities in forests was relatively low, and the variation of antibiotic concentrations was more stable contrasting with cropland and orchard. 4.2. Vertical distribution of antibiotics in soils Our study delineated the vertical distribution of antibiotics in soils at the catchment scale, and the results showed that there were high concentrations of TCs, QNs, and SAs in topsoil in all land use types both in summer and winter, while the concentrations of MLs were lower (Table 2). This was because different antibiotics have different mechanisms that can affect their environmental behaviors, such as in terms of sorption and leaching. Levels of antibiotic compounds were more prone to be affected by physical or chemical reactions within the soil matrix. Pan and Chu (2017a) reviewed the available literature values for partitioning coefficients (Kd) of antibiotics in soils. For instance, CTC has high Kd values ranging from 1280 to 2386 in clay loam and sandy loam. Sorption of fluoroquinolones was also strong (260 < Kd < 5791 L/kg in clay loam) and Kd values of sulfonamides ranged from 0.6 to 206 in soils. Observed ERY Kd values ranged from 9.35 to 309 in soil matrix (Schafhauser et al., 2018). Compared with the other antibiotic compounds, SAs are more photosensitive due to their molecular structure featuring aromatic rings and amine moiety (Boreen et al., 2003). Moreover, MLs and SAs exhibit weak sorption to soil with low adsorption coefficients (Ostermann et al., 2013; Rabolle and Spliid, 2000). Therefore, the concentration of MLs increased with soil depth (Table 2). However, the sorption of SAs was so weak that their transport was comparatively high due to runoff, and stronger than their leaching ability (Sura et al., 2016). Conversely, TCs, QNs, and SAs were increasing with depth due to subsequent ploughing in other manure-amended fields (Wei et al., 2016). In our study area, the lack of soil tillage could be the main reason why the opposite conclusion is drawn, because of the characteristics of crops and farming. 4.3. Correlation between antibiotics in soils and landscape structure Few studies have hitherto focused on the effects of land use structure on soil antibiotic concentrations. In our study, spatial distribution analysis of soil antibiotics showed that total antibiotic concentrations changed significantly with the proportion of cropland area indicating the intensity of agricultural activities (Fig. S4). There was greater demand for organic produce in SC4 due to higher village area and population. As a result, intensive cultivation strategies and higher fertilization rates were pursued, accompanied by more serious contamination of soil by antibiotics. Moreover, animal manures were applied in SC4 cropland due to the high density of animal breeding in the area, while commercial organic fertilizer after composting was favored in the other sub-catchments. However, during manure composting, some antibiotics could be greatly reduced or completely removed (Xie et al., 2016). Runoff and wastewater from animal farms could also increase the concentrations of antibiotics in ambient soils. According to other investigations, residual antibiotics in surrounding soils of animal farms exhibit relatively high concentrations ranging from n. d. to 6400 ng/g (Hu et al., 2010; Ji et al., 2012). The weak positive correlations between total antibiotic concentrations and extent of villages and towns might attest to the discharge of domestic wastewater or sewage sludge (Fairbairn et al., 2016). Our results suggest that human activities might be important contributors of

antibiotics in soils but the effects of structure and intensity of land uses on soil antibiotic levels require further study. 4.4. Effects of anthropogenic and environmental parameters on soil antibiotics There are seasonal changes in soil antibiotics under different land use types at the catchment scale. Our results suggested that there were higher antibiotic concentrations in winter, especially in cropland. One reason for this is the high manure usage rates in winter in the catchment (Zhou et al., 2017). Another reason is that the transportation and degradation of antibiotics is lower in winter due to lower temperatures and humidity. Photo- and biodegradation are the two principal routes for eliminating antibiotics and temperature and humidity have been confirmed as clearly influencing the degradation of antibiotics (Pan and Chu, 2017a). Thus, there were relatively high levels of antibiotics in soils in winter. Additionally, dilution or transport through higher rainfall in summer (monsoon) could affect the distribution of antibiotics in soils (Awad et al., 2014). Antibiotics persist in soil through soil tillage management practices such as long-term fertilization and irrigation (Christou et al., 2017). In general, the environmental input of antibiotics was determined by human activities, which was significantly affect the concentrations of antibiotics in soils. Thus, traditional tillage with lower inputs of antibiotics in agricultural fields in the study area would also lead to low levels of soil antibiotics. Numerous factors can affect the spatial and temporal variation of antibiotics in soils, such as soil physico-chemical properties, cultivation strategies, hydrological conditions and the loading mass, persistence, and transport of antibiotics (Luo et al., 2011; Zhou et al., 2013). Soil pH is an important factor affecting the sorption and degradation of antibiotics (Pan and Chu, 2017a). Surface charge of soil and antibiotics depends on soil pH, concomitantly affecting the sorption and migration of antibiotics. SAs (e.g., sulfapyridine, sulfameter, and sulfadimethoxine) exhibit relatively high sorption around pH 6, and OTC is adsorbed strongly in soil with metal-complexation chemistry around pH 8 (Park and Huwe, 2016; Zhang et al., 2014). In this study, soil pH ranged from 4.02 to 6.91 and was positively correlated with particular compounds including QNs, SAs and MLs (Fig. 4a). Available K also exhibited a positive correlation with most TCs and QNs, which implies that nutrients and antibiotics derive from similar sources, mainly manures and mineral fertilizer (Lin et al., 2016). Soil particle size also significantly affects sorption and leaching (Pan and Chu, 2017b). Although soil clay content was an indicator of antibiotics’ sorption, there were negative correlations between soil clay content and some antibiotic compounds according to our results. This might be influenced by metal ions or organic matter in soils, which can participate in the adsorption of antibiotics (Table S6). It has been reported that Fe3þ and Al3þ can increase OTC adsorption in humic acid through ternary complex formation between OTC, metal cations, and organic matter ligand groups (MacKay and Canterbury, 2005). The presence of humic acid also can significantly increase TC and CIP sorption dramatically on goethite under acidic condition, especially in presence of Cu2þ (Zhao et al., 2011; Tan et al., 2015). However, some metal ions can competed adsorption sites with antibiotic compounds. High Ca2þ humic acid showed lower adsorption coefficient for OTC around pH 5 (MacKay and Canterbury, 2005). In brief, our results suggested the organic matter can promote the antibiotic retention in soils through metalbridging in the study area. Our results also suggested that Actinobacteria was the predominant influencing bacterial species in agricultural soils under long-term application of manures (Fig. 4c). Previous studies have

F. Zhao et al. / Chemosphere 211 (2018) 261e270

shown that the biodegradation of antibiotics in soils is accelerated in the presence of diverse and abundant resistant bacteria (Schofield, 2018). Acinetobacter and Pseudomonas are dominant organisms involved in the degradation of sulfonamide in sludge, and Pseudomonas is also involved in SMX degradation in activated sludge (Yang et al., 2016a). Actinobacteria proportions increased under TC and SMX selection pressures, and Proteobacteria and Bacteroidetes decreased (Zhang et al., 2016b). Firmicutes and Bacteroidetes dominate in terms of sulfanilamide degradation (Liao et al., 2016b). Although there were significant effects of bacterial communities on antibiotic degradation, human activities and soil physico-chemical properties were the principal determinants of the distribution of antibiotics in soils (Fig. 5). Further detailed investigations of antibiotics and their ecosystem responses are needed in future. Our results suggested that the effects of anthropogenic factors on the distribution of antibiotics in soils in winter were strong due to agricultural activities, and the effects of environmental factors were not significant. In summer, human activities and their interactions with environmental factors were the dominant contributors to the variation of antibiotics in soils. Our results clearly suggest that antibiotics in peri-urban agricultural soils need to be monitored, evaluated, and controlled. 5. Conclusions This study focused on the spatial distribution of antibiotic concentrations and their seasonal variation in soils by field sampling and laboratory analysis. The results suggest that land use determines the spatial distribution of antibiotics in soils. Antibiotic concentrations were higher in cropland than forests and orchards. TCs and QNs showed significantly higher concentrations in cropland soils, and MLs were also present in relatively high concentrations in forest soils. The predominant classes of antibiotics in soils were also different under different land use types. TCs and QNs were the main antibiotic contaminants in most soils. Additionally, the vertical distribution of antibiotics in soil showed similar trends across all land use types. As soil depth increased, there were slightly increasing concentrations of MLs and decreasing concentrations of TCs, QNs, and SAs. Broader spatial and seasonal variation of antibiotic concentrations were observed in the topsoil of agricultural fields. Soil physico-chemical properties, human activities, and microbial communities interactively contribute to the distribution of antibiotics in soils. Especially in peri-urban area, long-term intensive use of organic fertilizers was the major contributor to contamination of soil with antibiotics. To reduce potential risks, specific fertilization strategies need to be devised to decrease antibiotic loading. Acknowledgements This work was supported by the National Natural Science Foundation of China (41571130064 and 41701018), and the Youth Innovation Promotion Association, Chinese Academy of Sciences (2018057). We thanks the anonymous reviewers for their constructive comments and suggestions. Appendix A. Supplementary data Supplementary data related to this article can be found at https://doi.org/10.1016/j.chemosphere.2018.07.162. References Aminov, R.I., 2009. The role of antibiotics and antibiotic resistance in nature.

269

Environ. Microbiol. 11, 2970e2988.  he -Brendle , J., Marichal, C., Charlet, L., 2016. Enhanced Aristilde, L., Lanson, B., Mie interlayer trapping of a tetracycline antibiotic within montmorillonite layers in the presence of Ca and Mg. J. Colloid Interface Sci. 464, 153e159. he -Brendle , J., Lanson, B., Charlet, L., 2010. Interactions Aristilde, L., Marichal, C., Mie of oxytetracycline with a smectite clay: a spectroscopic study with molecular simulations. Environ. Sci. Technol. 44, 7839e7845. Awad, Y.M., Kim, S.C., Abd El-Azeem, S.A.M., Kim, K.H., Kim, K.R., Kim, K., Jeon, C., Lee, S.S., Ok, Y.S., 2014. Veterinary antibiotics contamination in water, sediment, and soil near a swine manure composting facility. Environ. Earth Sci. 71, 1433e1440. Boreen, A.L., Arnold, W.A., McNeill, K., 2003. Photodegradation of pharmaceuticals in the aquatic environment: a review. Aquat. Sci. 65, 320e341. Brown, M.T., Vivas, M.B., 2005. Landscape development intensity index. Environ. Monit. Assess. 101, 289e309. Christou, A., Karaolia, P., Hapeshi, E., Michael, C., Fatta-Kassinos, D., 2017. Long-term wastewater irrigation of vegetables in real agricultural systems: concentration of pharmaceuticals in soil, uptake and bioaccumulation in tomato fruits and human health risk assessment. Water Res. 109, 24e34. vre, G., 2018. Probing oxytetracycline Dolui, M., Rakshit, S., Essington, M.E., Lefe sorption mechanism on kaolinite in a single ion and binary mixtures with phosphate using in Situ ATR-FTIR Spectroscopy. Soil Sci. Soc. Am. J. https:// doi.org/10.2136/sssaj2018.01.0020. Fairbairn, D.J., Karpuzcu, M.E., Arnold, W.A., Barber, B.L., Kaufenberg, E.F., Koskinen, W.C., Novak, P.J., Rice, P.J., Swackhamer, D.L., 2016. Sources and transport of contaminants of emerging concern: a two-year study of occurrence and spatiotemporal variation in a mixed land use watershed. Sci. Total Environ. 551, 605e613. Ferrey, M.L., Coreen Hamilton, M., Backe, W.J., Anderson, K.E., 2018. Pharmaceuticals and other anthropogenic chemicals in atmospheric particulates and precipitation. Sci. Total Environ. 612, 1488e1497. Figueroa, R.A., Leonard, A., MacKay, A.A., 2004. Modeling tetracycline antibiotic sorption to clays. Environ. Sci. Technol. 38, 476e483. Hammesfahr, U., Heuer, H., Manzke, B., Smalla, K., Thiele-Bruhn, S., 2008. Impact of the antibiotic sulfadiazine and pig manure on the microbial community structure in agricultural soils. Soil Biol. Biochem. 40, 1583e1591. Ho, Y.B., Zakaria, M.P., Latif, P.A., Saari, N., 2014. Occurrence of veterinary antibiotics and progesterone in broiler manure and agricultural soil in Malaysia. Sci. Total Environ. 488, 261e267. Hou, J., Wan, W.N., Mao, D.Q., Wang, C., Mu, Q.H., Qin, S.Y., Luo, Y., 2015. Occurrence and distribution of sulfonamides, tetracyclines, quinolones, macrolides, and nitrofurans in livestock manure and amended soils of Northern China. Environ. Sci. Pollut. Res. 22, 4545e4554. Hu, X.G., Zhou, Q.X., Luo, Y., 2010. Occurrence and source analysis of typical veterinary antibiotics in manure, soil, vegetables and groundwater from organic vegetable bases, northern China. Environ. Pollut. 158, 2992e2998. Ji, X.L., Shen, Q.H., Liu, F., Ma, J., Xu, G., Wang, Y.L., Wu, M.H., 2012. Antibiotic resistance gene abundances associated with antibiotics and heavy metals in animal manures and agricultural soils adjacent to feedlots in Shanghai; China. J. Hazard Mater. 235, 178e185. Karci, A., Balcioglu, I.A., 2009. Investigation of the tetracycline, sulfonamide, and fluoroquinolone antimicrobial compounds in animal manure and agricultural soils in Turkey. Sci. Total Environ. 407, 4652e4664. Kay, P., Blackwell, P.A., Boxall, A.B.A., 2005. Column studies to investigate the fate of veterinary antibiotics in clay soils following slurry application to agricultural land. Chemosphere 60, 497e507. Kümmerer, K., 2009a. Antibiotics in the aquatic environment - a review - part I. Chemosphere 75, 417e434. Kümmerer, K., 2009b. Antibiotics in the aquatic environment - a review - part II. Chemosphere 75, 435e441. Kümmerer, K., 2010. Pharmaceuticals in the environment. Annu. Rev. Environ. Resour. 35, 57e75. Kuppusamy, S., Kakarla, D., Venkateswarlu, K., Megharaj, M., Yoon, Y.-E., Lee, Y.B., 2018. Veterinary antibiotics (VAs) contamination as a global agro-ecological issue: a critical view. Agric. Ecosyst. Environ. 257, 47e59. Li, C., Chen, J.Y., Wang, J.H., Ma, Z.H., Han, P., Luan, Y.X., Lu, A.X., 2015. Occurrence of antibiotics in soils and manures from greenhouse vegetable production bases of Beijing, China and an associated risk assessment. Sci. Total Environ. 521, 101e107. Li, J., Xin, Z., Zhang, Y., Chen, J., Yan, J., Li, H., Hu, H., 2017. Long-term manure application increased the levels of antibiotics and antibiotic resistance genes in a greenhouse soil. Appl. Soil Ecol. 121, 193e200. Li, Y.W., Wu, X.L., Mo, C.H., Tai, Y.P., Huang, X.P., Xiang, L., 2011. Investigation of sulfonamide, tetracycline, and quinolone antibiotics in vegetable farmland soil in the Pearl River Delta area, Southern China. J. Agric. Food Chem. 59, 7268e7276. Liang, Y., Pei, M., Wang, D., Cao, S., Xiao, X., Sun, B., 2017. Improvement of soil ecosystem multifunctionality by dissipating manure-induced antibiotics and resistance genes. Environ. Sci. Technol. 51, 4988e4998. Liao, X., Li, B., Zou, R., Dai, Y., Xie, S., Yuan, B., 2016a. Biodegradation of antibiotic ciprofloxacin: pathways, influential factors, and bacterial community structure. Environ. Sci. Pollut. Res. 23, 7911e7918. Liao, X., Li, B., Zou, R., Xie, S., Yuan, B., 2016b. Antibiotic sulfanilamide biodegradation by acclimated microbial populations. Appl. Microbiol. Biotechnol. 100, 2439e2447.

270

F. Zhao et al. / Chemosphere 211 (2018) 261e270

Lin, H., Sun, W., Zhang, Z., Chapman, S.J., Freitag, T.E., Fu, J., Zhang, X., Ma, J., 2016. Effects of manure and mineral fertilization strategies on soil antibiotic resistance gene levels and microbial community in a paddy-upland rotation system. Environ. Pollut. 211, 332e337. Luo, Y., Xu, L., Rysz, M., Wang, Y.Q., Zhang, H., Alvarez, P.J.J., 2011. Occurrence and transport of tetracycline, sulfonamide, quinolone, and macrolide antibiotics in the Haihe River Basin, China. Environ. Sci. Technol. 45, 1827e1833. MacKay, A.A., Canterbury, B., 2005. Oxytetracycline sorption to organic matter by metal-bridging. J. Environ. Qual. 34, 1964e1971. McLaren, T.I., Guppy, C.N., Tighe, M.K., Forster, N., Grave, P., Lisle, L.M., Bennett, J.W., 2012. Rapid, nondestructive total elemental analysis of vertisol soils using portable X-ray fluorescence. Soil Sci. Soc. Am. J. 76, 1436e1445. Martinez, J.L., 2009. Environmental pollution by antibiotics and by antibiotic resistance determinants. Environ. Pollut. 157, 2893e2902. Martinez-Carballo, E., Gonzalez-Barreiro, C., Scharf, S., Gans, O., 2007. Environmental monitoring study of selected veterinary antibiotics in animal manure and soils in Austria. Environ. Pollut. 148, 570e579. Nogues-Bravo, D., Araujo, M.B., Romdal, T., Rahbek, C., 2008. Scale effects and human impact on the elevational species richness gradients. Nature 453, 216eU218. Ostermann, A., Siemens, J., Welp, G., Xue, Q.Y., Lin, X.Y., Liu, X.J., Amelung, W., 2013. Leaching of veterinary antibiotics in calcareous Chinese croplands. Chemosphere 91, 928e934. Pan, M., Chu, L.M., 2017a. Fate of antibiotics in soil and their uptake by edible crops. Sci. Total Environ. 599e600, 500e512. Pan, M., Chu, L.M., 2017b. Leaching behavior of veterinary antibiotics in animal manure-applied soils. Sci. Total Environ. 579, 466e473. Park, J.Y., Huwe, B., 2016. Effect of pH and soil structure on transport of sulfonamide antibiotics in agricultural soils. Environ. Pollut. 213, 561e570. Pils, J.R.V., Laird, D.A., 2007. Sorption of tetracycline and chlortetracycline on K- and Ca-saturated soil clays, humic substances, and clayhumic complexes. Environ. Sci. Technol. 41, 1928e1933. Qiao, M., Ying, G.G., Singer, A.C., Zhu, Y.G., 2018. Review of antibiotic resistance in China and its environment. Environ. Int. 110, 160e172. Qin, Q., Chen, X., Zhuang, J., 2017. The surface-pore integrated effect of soil organic matter on retention and transport of pharmaceuticals and personal care products in soils. Sci. Total Environ. 599e600, 42e49. Rabolle, M., Spliid, N.H., 2000. Sorption and mobility of metronidazole, olaquindox, oxytetracycline and tylosin in soil. Chemosphere 40, 715e722. Rabølle, M., Spliid, N.H., 2000. Sorption and mobility of metronidazole, olaquindox, oxytetracycline and tylosin in soil. Chemosphere 40, 715e722. Rahman, M.M., Shan, J., Yang, P., Shang, X., Xia, Y., Yan, X., 2018. Effects of long-term pig manure application on antibiotics, abundance of antibiotic resistance genes (ARGs), anammox and denitrification rates in paddy soils. Environ. Pollut. 240, 368e377. Riaz, L., Mahmood, T., Khalid, A., Rashid, A., Ahmed Siddique, M.B., Kamal, A., Coyne, M.S., 2018. Fluoroquinolones (FQs) in the environment: a review on their abundance, sorption and toxicity in soil. Chemosphere 191, 704e720. Schafhauser, B.H., Kristofco, L.A., de Oliveira, C.M.R., Brooks, B.W., 2018. Global review and analysis of erythromycin in the environment: occurrence, bioaccumulation and antibiotic resistance hazards. Environ. Pollut. 238, 440e451. Schofield, C.J., 2018. Antibiotics as food for bacteria. Nat. Microbiol. 3, 752e753. Sun, J., Zeng, Q., Tsang, D.C.W., Zhu, L.Z., Li, X.D., 2017. Antibiotics in the agricultural soils from the Yangtze River Delta, China. Chemosphere 189, 301e308. Sura, S., Degenhardt, D., Cessna, A.J., Larney, F.J., Olson, A.F., McAllister, T.A., 2016. Transport of three antimicrobials in runoff from windrows of composting beef cattle manure. J. Environ. Qual. 45, 494e502. Tasho, R.P., Cho, J.Y., 2016. Veterinary antibiotics in animal waste, its distribution in soil and uptake by plants: a review. Sci. Total Environ. 563, 366e376. Thiele-Bruhn, S., Beck, I.C., 2005. Effects of sulfonamide and tetracycline antibiotics on soil microbial activity and microbial biomass. Chemosphere 59, 457e465.

Tolls, J., 2001. Sorption of veterinary pharmaceuticals in soils: a review. Environ. Sci. Technol. 35, 3397e3406. Tan, Y., Guo, Y., Gu, X., Gu, C., 2015. Effects of metal cations and fulvic acid on the adsorption of ciprofloxacin onto goethite. Environ. Sci. Pollut. Res. 22, 609e617. Van Boeckel, T.P., Gandra, S., Ashok, A., Caudron, Q., Grenfell, B.T., Levin, S.A., Laxminarayan, R., 2014. Global antibiotic consumption 2000 to 2010: an analysis of Cross Mark 742 national pharmaceutical sales data. Lancet Infect. Dis. 14, 742e750. Vazquez-Roig, P., Andreu, V., Blasco, C., Pico, Y., 2012. Risk assessment on the presence of pharmaceuticals in sediments, soils and waters of the Pego-Oliva Marshlands (Valencia, eastern Spain). Sci. Total Environ. 440, 24e32. Wei, R., Ge, F., Zhang, L., Hou, X., Cao, Y., Gong, L., Chen, M., Wang, R., Bao, E., 2016. Occurrence of 13 veterinary drugs in animal manure-amended soils in Eastern China. Chemosphere 144, 2377e2383. Wu, D., Huang, Z.T., Yang, K., Graham, D., Xie, B., 2015. Relationships between antibiotics and antibiotic resistance gene levels in municipal solid waste leachates in Shanghai, China. Environ. Sci. Technol. 49, 4122e4128. Xie, W.Y., Yang, X.P., Li, Q., Wu, L.H., Shen, Q.R., Zhao, F.J., 2016. Changes in antibiotic concentrations and antibiotic resistome during commercial composting of animal manures. Environ. Pollut. 219, 182e190. Xie, W.Y., Shen, Q., Zhao, F.J., 2018. Antibiotics and antibiotic resistance from animal manures to soil: a review. Eur. J. Soil Sci. 69, 181e195. Yang, C.W., Hsiao, W.C., Chang, B.V., 2016a. Biodegradation of sulfonamide antibiotics in sludge. Chemosphere 150, 559e565. Yang, Y., Owino, A.A., Gao, Y., Yan, X., Xu, C., Wang, J., 2016b. Occurrence, composition and risk assessment of antibiotics in soils from Kenya, Africa. Ecotoxicology 25, 1194e1201. Zhang, H., Zhou, Y., Huang, Y., Wu, L., Liu, X., Luo, Y., 2016a. Residues and risks of veterinary antibiotics in protected vegetable soils following application of different manures. Chemosphere 152, 229e237. Zhang, Q.Q., Ying, G.G., Pan, C.G., Liu, Y.S., Zhao, J.L., 2015. Comprehensive evaluation of antibiotics emission and fate in the river basins of China: source Analysis, multimedia modeling, and linkage to bacterial resistance. Environ. Sci. Technol. 49, 6772e6782. Zhang, Y., Geng, J., Ma, H., Ren, H., Xu, K., Ding, L., 2016b. Characterization of microbial community and antibiotic resistance genes in activated sludge under tetracycline and sulfamethoxazole selection pressure. Sci. Total Environ. 571, 479e486. Zhang, Y.L., Lin, S.S., Dai, C.M., Shi, L., Zhou, X.F., 2014. Sorption-desorption and transport of trimethoprim and sulfonamide antibiotics in agricultural soil: effect of soil type, dissolved organic matter, and pH. Environ. Sci. Pollut. Res. 21, 5827e5835. Zhao, X., Wang, J., Zhu, L., Ge, W., Wang, J., 2017. Environmental analysis of typical antibiotic-resistant bacteria and ARGs in farmland soil chronically fertilized with chicken manure. Sci. Total Environ. 593e594, 10e17. Zhao, Y., Geng, J., Wang, X., Gu, X., Gao, S., 2011. Tetracycline adsorption on kaolinite: pH, metal cations and humic acid effects. Ecotoxicology 20, 1141e1147. Zheng, S., Hu, J., Chen, K., Yao, J., Yu, Z., Lin, X., 2009. Soil microbial activity measured by microcalorimetry in response to long-term fertilization regimes and available phosphorous on heat evolution. Soil Biol. Biochem. 41, 2094e2099. Zhou, L.J., Ying, G.G., Liu, S., Zhang, R.Q., Lai, H.J., Chen, Z.F., Pan, C.G., 2013. Excretion masses and environmental occurrence of antibiotics in typical swine and dairy cattle farms in China. Sci. Total Environ. 444, 183e195. Zhou, X., Qiao, M., Wang, F.H., Zhu, Y.G., 2017. Use of commercial organic fertilizer increases the abundance of antibiotic resistance genes and antibiotics in soil. Environ. Sci. Pollut. Res. 24, 701e710. Zhu, Y.G., Zhao, Y., Li, B., Huang, C.L., Zhang, S.Y., Yu, S., Chen, Y.S., Zhang, T., Gillings, M.R., Su, J.Q., 2017. Continental-scale pollution of estuaries with antibiotic resistance genes. Nat. Microbiol. 2, 16270.