Leaching behavior of veterinary antibiotics in animal manure-applied soils

Effects of land use and rainfall on sequestration of veterinary antibiotics in soils at the hillslope scale

Veterinary antibiotics have been detected as contaminants of emerging concern in soil environment worldwide. Animal manure is frequently applied to agricultural fields to improve soil fertility, which can result in introducing large amount of antibiotics into soil environment. However, few attempts have been made to identify the spatial and temporal dynamics of veterinary antibiotics in soil at the hillslope scale with different land uses. This study was performed to explore the pattern and variability of veterinary antibiotics in the soil in response to rainfall events. Results showed that higher concentrations of veterinary antibiotics were generally found in cropland (292.6 ± 280.1 ng/g) and orchard (228.1 ± 230.5 ng/g) than in forestland (13.5 ± 9.9 ng/g). After rainfall events, antibiotics accumulated in the soil at the positions where manure was applied, especially under high-intensity rainfall conditions. However, the antibiotic concentration in soil slightly increased from the top to the bottom of hills, thus indicating the restricted contribution of runoff to antibiotic transport, especially under low-intensity rainfall conditions. In addition, most antibiotics were sequestered in the surface soil (0-10 cm), and higher antibiotic concentrations were observed in deep soil (20-40 cm) in cropland than orchard. The soil aggregate, organic matter, and clay content played important roles in antibiotic sequestration along the hillslope subject to low-, medium-, and large-amount rainfall events, respectively. This study identified that land use, rainfall conditions, and soil structures jointly affect the spatial and temporal variability of antibiotics in soils on hillslopes.

The grey water footprint of human and veterinary pharmaceuticals

Water pollution by pharmaceuticals is widespread, causing both environmental and human health risks. We assess pharmaceutical water pollution from human and veterinary pharmaceuticals at three geographical levels: global, national (considering Germany and the Netherlands) and catchment level (with a case study for the Vecht catchment shared by Germany and the Netherlands). The grey water footprint (GWF), a measure of water pollution in volumetric terms, is estimated from pharmaceutical loads entering the aquatic environment, considering different pollutant sources and pathways. We study different substances depending on data availability, which varies across geographical levels. Results show a global per capita GWF of 1900 m³ yr^-1 resulting from human consumption of ciprofloxacin. The largest GWFs in both Germany and the Netherlands were found for ethinylestradiol for human and amoxicillin for veterinary use. The estimated per capita GWF from human use of ethinylestradiol is 2300 m³ yr^-1 for Germany and 11,300 m³ yr^-1 for the Netherlands. The per capita GWFs of German and Dutch consumers of animal products are 12,900 and 10,600 m³ yr^-1, respectively. For the Vecht catchment, we estimate the water pollution level per sub-catchment by comparing the GWF to available runoff, which enables us to identify geographic hotspots. In the basin as a whole, GWFs from human and veterinary pharmaceuticals both exceed available runoff. At all levels, pharmaceutical water pollution substantially adds to earlier water footprint studies that excluded this type of pollution, which demonstrates the importance to include pharmaceutics in water footprint studies.

Insight into dynamics and bioavailability of antibiotics in paddy soils by in situ soil moisture sampler

Plant-soil systems have complex regulatory mechanisms for xenobiotics uptake by plant, and these chemicals in soil pore water (SPW) are regarded as the bioavailable fraction. To date, little is known about the role of SPW in regard to the bioavailability of antibiotics for plant. In this study, in situ soil moisture sampler (SMS) was adopted to collect SPW from four paddy soils without disrupting the rhizosphere zone to evaluate antibiotic uptake in rice. The results show that SMS is applicable for antibiotics that have small molecular sizes and Log K_ow values, e.g., sulfadiazine (SDZ), sulfamethoxazole (SMZ), trimethoprim (TRM), and florfenicol (FLR). However, SMS performance was not feasible for large size and medium hydrophobic clarithromycin (CLR). Antibiotics in SPW demonstrated differences among chemicals and soils. Relatively higher levels of SDZ, SMZ, and FLR were observed in SPW than TRM, and neutral Panjin soil had the highest levels of antibiotics in SPW among four soils. The levels of antibiotics in SPW were negatively correlated with their soil partition parameter, K_d. Rapid decreases of SMZ, FLR, and SDZ in the SPW were consistent with their low residues in the final soils. All antibiotics were detectable in rice roots, followed by low detection levels in a few shoot samples, while no antibiotics were detectable in the grains of four soils. Relatively higher levels of SDZ, SMZ and FLR were observed in the roots of Panjin soil, consistent with their levels in SPW and K_d values. Furthermore, CLR and TRM were observed to have higher levels in roots, which was regarded as a consequence of their relatively longer persistence. Our study indicates that SMS is an applicable technique for in situ sampling of SPW, and level of antibiotics in SPW can work as a useful indicator to explore their bioavailability to plants.

Emergence of Escherichia coli harbouring mcr-1 and mcr-3 genes in North West Algerian farmlands

OBJECTIVES

Colistin resistance has emerged worldwide, threatening the efficacy of colistin treatment of Gram-negative bacterial infections. Farms have been recognised as an important reservoir of genes conferring resistance to colistin. This study aimed to isolate and characterise colistin-resistant bacteria in farmlands located in the region of Oran, northwest Algeria.

METHODS

Forty environmental samples were collected between May 2016 and March 2018 at eight agricultural sites in the Oran region.

RESULTS

From the 40 samples, 103 colistin-resistant isolates were isolated from agricultural soil (n = 52), irrigation water (n = 31) and manure (n = 20). Eight isolates were identified as Escherichia coli, including six and two isolates carrying the mcr-1 and mcr-3 gene, respectively. All eight E. coli isolates were non-susceptible to amoxicillin, amoxicillin/clavulanic acid, ticarcillin, nalidixic acid, ciprofloxacin, gentamicin, trimethoprim/sulfamethoxazole and rifamycin; two were also non-susceptible to cefotaxime, cefepime and aztreonam and carried the bla_TEM-12 gene in addition to mcr-1. The six mcr-1-carrying E. coli isolates (MIC ≥ 2 μg/mL) belonged to three sequences types, including ST10 (n = 3), ST405 (n = 2) and ST345 (n = 1), whereas the two mcr-3-carrying isolates were assigned to ST155. The conjugation assay was positive only for two mcr-1-positive isolates.

CONCLUSION

These results show that farms are an important reservoir of colistin-resistant E. coli as well as other antimicrobial resistance genes such as ESBL genes. Transfer of manure from animals to soil and irrigation water might be disseminating a mix of multiple resistances, posing a worrying threat to human health.

Methods for field measurement of antibiotic concentrations: limitations and outlook

The growing prevalence of antibiotic resistance poses an increasingly serious threat to human health. Although an important driver of antibiotic resistance is the continuous exposure of bacteria to sublethal concentrations of antibiotics in natural environments, antibiotic pollutants are not currently tracked globally or systematically. This limits the international capacity to address the rise of antibiotic resistance at its source. To address this lack of data, the development of methods to measure antibiotic concentrations on-site is essential. These methods, ideally, must be sensitive to sublethal concentrations of antibiotics and require minimal technical expertise. Furthermore, factors such as cost, selectivity, biosafety and the ability to multiplex must be evaluated in the context of field use. Based on these criteria, we provide a critical review of current methods in antibiotic detection and evaluate their adaptability for use on-site. We categorize these methods into microbiological assays, physical and chemical assays, immunoassays, aptasensors and whole-cell biosensors. We recommend continued development of a dipstick or microfluidics approach with a bacterial promoter-based mechanism and colorimetric output. This technique would incorporate the advantageous aspects of existing methods, maximize shelf-life and ease-of-use, and require minimal resources to implement in the field.

Metabolism of Sulfamethoxazole by the Model Plant Arabidopsis thaliana

Phytometabolism of antibiotics is a potentially significant route of human exposure to trace concentrations of antibiotics, prompting concerns about antibiotic resistance. The present study evaluated the metabolism of sulfamethoxazole (SMX), a commonly used sulfonamide antibiotic, by Arabidopsis thaliana. SMX was intensively metabolized by A. thaliana, with only 1.1% of SMX in plant tissues present as the parent compound after 10 days of exposure. Untargeted screening of extractable metabolites revealed that N-glycosylation was the main transformation pathway of SMX in A. thaliana plants, with N⁴-glycosyl-SMX accounting for more than 80% of the extractable metabolites. Additionally, N⁴-glycosyl-glycoside SMX accounted for up to 4.4% of the extractable metabolites, indicating glycosylation of N⁴-glycosyl-SMX. The majority of minor extractable SMX metabolites were also conjugates of the parent compound, such as pterin-SMX and methyl salicylate-SMX conjugates. In ¹⁴C-SMX trials, ¹⁴C-radioactivity was detected in both extractable and bound residues in plant tissues. Extractable residues, which included ¹⁴C-SMX and its soluble metabolites, accounted for 35.8-43.6% of the uptaken ¹⁴C-radioactivity, while bound residues were 56.4-64.2%. Approximately 27.0% of the initially applied ¹⁴C-radioactivity remained in the culture media at the conclusion of the experiments, composed of both ¹⁴C-SMX and its metabolites, likely due to plant excretion.

Soil contamination with antibiotics in a typical peri-urban area in eastern China: Seasonal variation, risk assessment, and microbial responses

The prevalence and persistence of antibiotics in soils has become an emerging environmental issue and an increasing threat to soil security and global public health. The problem is more severe in areas undergoing rapid urbanization; however, the ecological risks of antibiotics, seasonal variability, and associated soil microbial responses in peri-urban soils have not been well-explored. The seasonal soil sampling campaigns were conducted in a typical peri-urban watershed in eastern China to investigate distribution of antibiotics. The results demonstrated higher mean concentrations of most antibiotic compounds in winter than in summer in peri-urban soils. The seasonal variations of norfloxacin, enrofloxacin, and ciprofloxacin were more significant than those of other antibiotics, due to their higher migration ability and bioavailability. An ecological risk assessment demonstrated that chlortetracycline, ciprofloxacin, doxycycline, and ofloxacin can pose high risks to soil microorganisms. Furthermore, the coexistence of multiple antibiotics obviously poses higher risks than individual compounds. A redundancy analysis demonstrated that tetracyclines mainly showed negative correlations with Firmicutes and Chloroflexi, and quinolones showed obviously negative correlations with Acidobacteria, Gemmatimonadetes, and Nitrospirae, suggesting potential inhibition from antibiotics on biological activities or biodegradation processes. However, the persistence of antibiotics in soil results in a significant decrease in bacterial diversity and a change in dominant species. Our results provide an overview of the seasonal variability of antibiotics and the associated effects on bacterial communities in peri-urban soils. The results can provide scientific guidance on decreasing soil contamination with antibiotics to enhance soil security in similar areas.

Antibiotics in the Soil Environment-Degradation and Their Impact on Microbial Activity and Diversity

Antibiotics play a key role in the management of infectious diseases in humans, animals, livestock, and aquacultures all over the world. The release of increasing amount of antibiotics into waters and soils creates a potential threat to all microorganisms in these environments. This review addresses issues related to the fate and degradation of antibiotics in soils and the impact of antibiotics on the structural, genetic and functional diversity of microbial communities. Due to the emergence of bacterial resistance to antibiotics, which is considered a worldwide public health problem, the abundance and diversity of antibiotic resistance genes (ARGs) in soils are also discussed. When antibiotic residues enter the soil, the main processes determining their persistence are sorption to organic particles and degradation/transformation. The wide range of DT50 values for antibiotic residues in soils shows that the processes governing persistence depend on a number of different factors, e.g., physico-chemical properties of the residue, characteristics of the soil, and climatic factors (temperature, rainfall, and humidity). The results presented in this review show that antibiotics affect soil microorganisms by changing their enzyme activity and ability to metabolize different carbon sources, as well as by altering the overall microbial biomass and the relative abundance of different groups (i.e., Gram-negative bacteria, Gram-positive bacteria, and fungi) in microbial communities. Studies using methods based on analyses of nucleic acids prove that antibiotics alter the biodiversity of microbial communities and the presence of many types of ARGs in soil are affected by agricultural and human activities. It is worth emphasizing that studies on ARGs in soil have resulted in the discovery of new genes and enzymes responsible for bacterial resistance to antibiotics. However, many ambiguous results indicate that precise estimation of the impact of antibiotics on the activity and diversity of soil microbial communities is a great challenge.

Transport of Potential Manure Hormone and Pharmaceutical Contaminants through Intact Soil Columns

Although adding manure to agricultural soils is a commonly practiced disposal method and a means to enhance soil productivity, potential environmental contamination by any associated chemicals of emerging concern (CECs) such as hormones and pharmaceuticals is not well understood. Our objective was to provide field-relevant predictions of soil transport and attenuation of 19 potential manure CECs using undisturbed soil columns irrigated under unsaturated conditions. The CEC concentrations in leached water were monitored for 13 wk using high performance liquid chromatography-time of flight-mass spectrometry (HPLC-TOF-MS), after which time soil in the cores was removed and sampled for extractable CECs. Compounds quantified in column leachate included all four of the added sulfonamide antibiotics and the nonsteroidal, anti-inflammatory drug flunixin. Only trace amounts of several of the seven hormones, five remaining antibiotics, and two antimicrobials leached from the columns from exogenous soil additions. Soil residues of all 19 compounds were detected, with highest extractable amounts for 17α-hydroxyprogesterone > triclosan (antimicrobial) > flunixin > oxytetracycline. Those CECs with the highest recoveries as calculated by summing leached and extractable amounts were flunixin (14.5%), 17α-hydroxyprogesterone (5.3%), triclosan (4.6%), and sulfadimethoxine (4.8%). Manure management to prevent CEC contamination should consider the potential environmental problems caused by negatively charged compounds with the greatest mobility (flunixin and sulfadimethoxine) and those that have long residence times in soil (triclosan, 17α-hydroxyprogesterone, flunixin, and oxytetracycline). Flunixin is particularly important given its mobility and long residence time in soil.

Assessment of Three Antimicrobial Residue Concentrations in Broiler Chicken Droppings as a Potential Risk Factor for Public Health and Environment

Tetracyclines, sulfonamides and amphenicols are broad spectrum antimicrobial drugs that are widely used in poultry farming. However, a high proportion of these drugs can be excreted at high concentrations in droppings, even after the end of a therapy course. This work intended to assess and compare concentrations of florfenicol (FF), florfenicol amine (FFa), chlortetracycline (CTC), 4-epi-chlortetracycline (4-epi-CTC), and sulfachloropyridazine (SCP) in broiler chicken droppings. To this end, 70 chickens were housed under controlled environmental conditions, and assigned to experimental groups that were treated with therapeutic doses of either 10% FF, 20% CTC, or 10% SCP. Consequently, we implemented and designed an in-house validation for three analytical methodologies, which allowed us to quantify the concentrations of these three antimicrobial drugs using liquid chromatography coupled to mass spectrometry (LC-MS/MS). Our results showed that FF and FFa concentrations were detected in chicken droppings up to day 10 after ceasing treatment, while CTC and 4-epi-CTC were detected up to day 25. As for SCP residues, these were detected up to day 21. Noticeably, CTC showed the longest excretion period, as well as the highest concentrations detected after the end of its administration using therapeutic doses.

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

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 (0-10, 10-20, 20-40 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.

Occurrence of β-lactam and polyether ionophore antibiotics in lagoon water and animal manure

The occurrence of micropollutants in agricultural wastes is an emerging area of interest due to the potential impact of these compounds on the environment. A sensitive and reliable analytical method using liquid chromatography-electrospray tandem mass spectrometry has been developed and validated for the determination of three β-lactam and three polyether ionophore antibiotics in lagoon water and animal manure matrices. The method was applied to evaluate the occurrence of these compounds from participating farms in northern Colorado. Seven of the 19 lagoon water samples and two of the six animal manures showed detectable. The three targeted β-lactams (cephapirin, penicillin G, cloxacillin) were found at 0.97-43.31 μg/L in the lagoon water samples. Of the three targeted polyether ionophores, only monensin (94 to 1077 μg/L) was detected in the beef runoff pond water samples. Only cloxacillin was measured in the dairy animal manure samples at levels from 8.09 to 45.20 μg/kg. No cephapirin, penicillin G, cloxacillin, salinomycin, or narasin A were detected in any solid animal manure sample. These results indicate that elevated concentrations of β-lactam and ionophore compounds might be found in lagoon or runoff pond waters and solid animal manures compared to surface waters, which these compounds are used in veterinary applications.

Functional Diversity of Soil Microbial Communities in Response to the Application of Cefuroxime and/or Antibiotic-Resistant Pseudomonas putida Strain MC1

Cefuroxime (XM), the most commonly prescribed antibiotic from the cephalosporin group, may cause changes in the structure of the soil microbial community, and these changes may also be reflected in the alteration of its functionality. Therefore, due to the lack of studies on this topic, the scope of this study was to assess the functional diversity and catabolic activity of the microbial community in soil treated with XM (1 mg/kg and 10 mg/kg soil) using the community-level physiological profile (CLPP) approach during a 90-day experiment. In addition, the effect of antibiotic-resistant Pseudomonas putida strain MC1 (Ps) was also evaluated. The resistance/resilience concept and multifactorial analysis were used to interpret the data. The results showed that the introduction of XM and/or Ps into the soil caused changes in the catabolic activity and functional diversity of the microbial community. A decrease in the values of the CLPP indices (i.e., microbial activity expressed as the average well-color development (AWCD), substrate richness (R), the Shannon-Wiener (H) and evenness (E) indices and the AWCD values for the six carbon substrate groups) for the XM-treated soil was generally detected up to 30 days. In turn, at the same time, the activity measured in the Ps-inoculated soil was higher compared to the control soil. A stimulatory effect of XM at 10 mg/kg (XM10) and XM10+Ps on the utilization pattern of each substrate group was found at the following sampling times (days 60 and 90). The AWCD values for the utilization of amines, amino acids, carbohydrates, carboxylic acids, miscellaneous compounds and polymers for these treatments were found to be up to 2.3-, 3.1-, 2.3-, 13-, 3.4- and 3.3-fold higher compared to the values for the nontreated control, respectively. The resistance of the CLPP indices and the AWCD values for the carbon substrate groups were categorized as follows: E > H > R > AWCD and amino acids = carbohydrates > polymers > amines > miscellaneous > carboxylic acids, respectively. The results suggest a low initial resistance of the soil microbial community to XM and/or Ps, and despite the short-term negative effect, the balance of the soil ecosystem may be disturbed.

Use of antibiotics in broiler production: Global impacts and alternatives

Antibiotics are used to fight bacterial infections. However, a selective pressure gave rise to bacteria resistant to antibiotics. This leaves scientists worried about the danger to human and animal health. Some strategies can be borrowed to reduce the use of antibiotics in chicken farms. Much research has been carried out to look for natural agents with similar beneficial effects of growth promoters. The aim of these alternatives is to maintain a low mortality rate, a good level of animal yield while preserving environment and consumer health. Among these, the most popular are probiotics, prebiotics, enzymes, organic acids, immunostimulants, bacteriocins, bacteriophages, phytogenic feed additives, phytoncides, nanoparticles and essential oils.

Occurrence of antibiotics and antibiotic resistance genes in soils from wastewater irrigation areas in the Pearl River Delta region, southern China

The occurrence and distribution of tetracycline (TC) and sulfamethazine (SMZ), and the corresponding antibiotic resistance genes (ARGs) were investigated in six agricultural sites in the Pearl River Delta (PRD) region in southern China. Irrigation water and irrigated soils at two different depths (0-10 and 10-20cm) were analyzed. The total concentrations of TC and SMZ in irrigation water ranged from 69.3 to 234ng/L and from 4.00 to 58.2ng/L, respectively, while the total concentrations of TC and SMZ in irrigated soils ranged from 5.00 to 21.9μg/kg and from 1.30 to 4.20μg/kg, respectively. After long-term irrigation with domestic and fishpond wastewater in the field, the residual TC and SMZ and their corresponding ARGs in soils were significantly higher in fishpond-irrigated soils (Dongguan and Shenzhen) than in domestic wastewater-irrigated soils (Foshan, Guangzhou, Huizhou and Zhongshan). The concentrations of antibiotics and their ARGs were significantly higher in irrigation water than in irrigated soils, which indicated that wastewater was the primary source of antibiotics in the soil environments. The domestic and fishpond wastewater were important repositories of antibiotics and their ARGs, which require effective treatment before their discharge into the environment. Other factors such as soil physicochemical properties, manure application, irrigation water sources and cropping patterns also affect the antibiotic concentrations and ARG abundances. The residual antibiotic concentrations statistically correlated with the corresponding ARGs in irrigation water and irrigated soils, both of which decreased with increasing soil depth, indicating that the concentration of antibiotics in the environment exerted a selection pressure on the microorganisms in the environment.

Graphene oxide-facilitated transport of levofloxacin and ciprofloxacin in saturated and unsaturated porous media

In this work, effects of graphene oxide (GO) on the co-transport of the two typical Fluoroquinolones (FQs) - levofloxacin (LEV) and ciprofloxacin (CIP) in saturated and unsaturated quartz sand media were studied. The adsorption isotherms showed that GO had much larger sorption capacities to LEV and CIP than sand with the largest Langmuir adsorption capacity of 409 mg g^-1 (CIP-GO); while the sorption affinity of the two FQs onto the two adsorbents might follow the order of CIP-sand > LEV-sand > LEV-GO > CIP-GO. GO promoted the mobility of the two FQs in both saturated and unsaturated porous media due to its strong mobility and sorption capacity. The GO-bound LEV/CIP was responsible for the LEV/CIP transport in the porous media, and transport of GO-bound FQs increased with the increasing of initial GO concentration. Under unsaturated conditions, moisture showed little effect on the transport of GO-bound CIP; however, the mobility of GO-bound LEV reduced with the decreasing of moisture content, suggesting the transport of adsorbed LEV from GO to air-water interface. GO sorption reduced the antibacterial ability of the two FQs, but they were still effective in inhibiting E. coli growth.

Transfer of antibiotics from wastewater or animal manure to soil and edible crops

Antibiotics are added to agricultural fields worldwide through wastewater irrigation or manure application, resulting in antibiotic contamination and elevated environmental risks to terrestrial environments and humans. Most studies focused on antibiotic detection in different matrices or were conducted in a hydroponic environment. Little is known about the transfer of antibiotics from antibiotic-contaminated irrigation wastewater and animal manure to agricultural soil and edible crops. In this study, we evaluated the transfer of five different antibiotics (tetracycline, sulfamethazine, norfloxacin, erythromycin, and chloramphenicol) to different crops under two levels of antibiotic-contaminated wastewater irrigation and animal manure fertilization. The final distribution of tetracycline (TC), norfloxacin (NOR) and chloramphenicol (CAP) in the crop tissues under these four treatments were as follows: fruit > leaf/shoot > root, while an opposite order was found for sulfamethazine (SMZ) and erythromycin (ERY): root > leaf/shoot > fruit. The growth of crops could accelerate the dissipation of antibiotics by absorption from contaminated soil. A higher accumulation of antibiotics was observed in crop tissues under the wastewater treatment than under manure treatment, which was due to the continual irrigation that increased adsorption in soil and uptake by crops. The translocation of antibiotics in crops mainly depended on their physicochemical properties (e.g. log K_ow), crop species, and the concentrations of antibiotics applied to the soil. The levels of antibiotics ingested through the consumption of edible crops under the different treatments were much lower than the acceptable daily intake (ADI) levels.

Fate of antibiotics in soil and their uptake by edible crops

Antibiotics are bioactive substances, and their use as human and animal medicines for illness prevention, disease treatment and growth promotion has increased in recent decades. They are excreted, either unchanged or metabolized, and are discharged to the environment through animal manure, municipal wastewater or biosolids. Consequently, these chemicals reach cropland, which is advocated as a means of recycling. As these drugs are used in escalating quantities, there is growing concern over their presence, toxicity and fate in the soil, which may pose adverse effects on plant growth and productivity, as well as result in their uptake and accumulation in crops. These will contaminate the food chain and eventually affect human health. In this review, we summarize recent research and provide a detailed overview of antibiotics in soil-plant systems, including 1) the occurrence and determination of antibiotics around the world and their routes of entry to the environment, 2) the impact of wastewater irrigation and animal manure or biosolids amendment on agricultural soils, 3) the transport and persistence of antibiotics in the terrestrial environment, and 4) the bioaccumulation and translocation of antibiotics in different tissues of edible crops under laboratory and field conditions. Their impacts on the environment and potential human exposure are elucidated. Knowledge gaps and future research perspectives are discussed.