Scholarly article on topic 'Occurrence and transformation of veterinary pharmaceuticals and biocides in manure: a literature review'

Occurrence and transformation of veterinary pharmaceuticals and biocides in manure: a literature review Academic research paper on "Environmental engineering"

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Academic research paper on topic "Occurrence and transformation of veterinary pharmaceuticals and biocides in manure: a literature review"

Wohde et al. Environ Sci Eur (2016) 28:23 DOI 10.1186/s12302-016-0091-8

0 Environmental Sciences Europe

REVIEW

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Occurrence and transformation of veterinary pharmaceuticals and biocides in manure: a literature review

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Manuel Wohde1*©, Silvia Berkner2, Thomas Junker3, Sabine Konradi2, Lisa Schwarz1 and Rolf-Alexander Düring1

Abstract

The spread of veterinary medicinal products (VMPs) and biocides via manure onto agriculturally used areas represents a very important emission into the environment for these product groups. Within this literature study, publicly available transformation studies with liquid manure are summarized. Transformation studies were evaluated regarding the transformation fate of tested substances, the origin and characteristics of used manure, the experimental setup, and the measured parameters. As main topics within the 42 evaluated transformation studies, the high dependency of transformation on temperature, redox potential, dry matter content, and other parameters is reported. Test duration throughout the studies ranged from 2 to 374 days and study temperature ranged from 5 to 55 °C. Only seven publications gave information on the redox potential of the manure. Further, the characterization of the matrix in many cases was inadequate due to missing parameters such as dry matter content or pH. Only three publications studied transformation of biocides. To allow for a consistent assessment of studies within the registration process, a harmonized internationally accepted and validated test method is needed. Additionally, monitoring data of VMPs in manure were collected from literature and evaluated regarding the origin and characteristics of the manure, the minimum/maximum found concentrations, and the percentage of identified compounds. Within the 27 evaluated publications, 1568 manure samples were analyzed and 39 different active substances for VMPs and 11 metabolites and transformation products of VMPs could be found in manure. Most often, the samples were analyzed for sulfonamides, tetracyclines, and fluoroquinolones. Not one study searched for biocides or worked with a non-target approach. For sulfadiazine and chlortetracycline, concentrations exceeding the predicted environmental concentrations were found.

Keywords: Veterinary medicines, Drug, Pharmaceuticals, Biocides, Manure, Slurry, Transformation, Dissipation, Degradation, Monitoring

Background

Veterinary medicinal products (VMPs) are excreted by the treated animals in the form of unchanged parent substances and metabolized compounds. The excrements from stabled animals in Europe and North America are collected and stored mainly as liquid or solid manure before they are used as fertilizers on arable land and grassland. Biocides, which are used for the disinfection

'Correspondence: manuel.wohde@umwelt.uni-giessen.de

1 Institute of Soil Science and Soil Conservation, IFZ, Justus Liebig

University Giessen, Heinrich-Buff-Ring 26-32, 35392 Giessen, Germany

Full list of author information is available at the end of the article

of stables, end up in the stored animal excrements. Via manure application in agriculture, veterinary medicines and biocides are released into the environment and consequently affect soil and water quality.

Depending on boundary conditions such as storage temperature, dry matter content, feeding of the animals, and availability of electron acceptors, the pharmaceuticals and biocides can be further transformed in the liquid manure. Besides transformation, other processes such as volatilization, sorption, and the formation of non-extractable residues (NER) can occur and contribute to the dissipation of the active ingredients.

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© 2016 The Author(s). This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.

Transformation products may also persist in environmental matrices and can be ecotoxic. For tetracyclines, transformation products like epimers, isomers, and anhydro-compounds were detected [5, 31]. Metabolites of sulfadiazine show transformation back to the parent compound [26]. Transformation processes are influenced by the composition of matrix, temperature, pH value, microbiology, as well as aerobic or anaerobic conditions. Compounds could adsorb to the matrix depending on its sorption capacity. The higher the dry matter content in liquid manure, the higher the number of sorption sites [35].

Generally, the transformation under aerobic conditions occurs faster than the transformation under anaerobic conditions. Also high temperatures promote the degradation of compounds in liquid manure. During manure storage in manure tanks, which is most common in Europe, the storage conditions are anaerobic. In North America, manure is often stored in lagoons because of the large amounts of manure that accumulates in large-scale concentrated animal feeding operations (CAFOs). The outdoor lagoon storage is distinguished by more aerobic conditions on the large lagoon water surface but also by anaerobic conditions in deeper layers. Composting the separated manure under aerobic conditions is a favored treatment of manure in Asia. Concluding, the transformation process of compounds is affected largely by the storage practice of manure.

There is increasing research activity regarding the transformation of single substances under laboratory conditions. Current guidance, e.g., the "guideline on determining the fate of veterinary medicinal products in manure" [19], takes transformation of VMPs and biocides in manure into account. However, there is no standardized experimental test protocol available to examine the transformation of veterinary medicinal products (VMPs) and biocides in liquid manure. The EMA guideline on transformation in manure [19] only contains basic regulatory requirements. To allow for a consistent assessment of studies within regulatory frameworks, a harmonized internationally accepted and validated test method is needed. The present review paper brings the initial situation assessment which might serve as a basis for further exploitation toward the formulation of the guideline.

This literature study first provides a survey on monitoring data of VMPs and biocides in liquid manure and secondly presents studies on transformation processes in liquid manure. The objective of this review is to consider the following questions: Which compounds are found in liquid manure? Which compounds are investigated? Which methods and analytical techniques are used and which factors have been identified affecting the transformation process in liquid manure?

Methods

The search engines and databases such as "Google Scholar" and "ISI Web of Knowledge" were used. Categorized search items are shown in Table 1. For Boolean search, the most relevant keywords from the first and the second category were combined with one of the keywords of categories 3-6.

International publications from the year 2000 to date were considered. In addition, cross-references of the found publications were evaluated. Further, relevant German authorities and organizations (German Federal State Ministries and Departments, private associations) were asked for reports on related topics.

By this means, 668 individual publications were obtained, 27 of which were found to measure or monitor the occurrence of VMPs in liquid manure. Examined substances, determined concentrations, origin of the manure, and further parameters were listed. From 668 records, 42 publications deal explicitly with transformation of veterinary medicinal products and biocides in manure. These citations were evaluated systematically, considering specific parameters such as investigated compounds and substance amounts, characterization of matrices, transformation products, methodology, and chemical analysis of the studies. Liquid manure generally is defined in the following way: "Liquid manure that is the predominant type of manure in Europe and North America is a mixture of urine, faces and water used to clean the stables and may also contain bedding material. Typical dry matter contents for pig and cattle manure have been found to be 5 and 10 %, respectively" [74]. Since many studies do not report the dry matter content of the analyzed manure or do not follow the common definition of liquid manure, only those transformation studies were excluded from this literature review, that clearly work with stable manure from manure heaps.

Occurrence of veterinary medicines and biocides in manure

The monitoring data tables (Tables 2, 3, 4, 5) summarize the results of 27 different publications measuring active ingredients of veterinary medicinal products in manure from the year 2000 until today. The analyses were conducted in North America (Canada), in Europe (Austria, Czech Republic, Denmark, Germany, Italy, Switzerland), and in Asia (China, Japan). Although the results give only information on specific locations, the ubiquitous occurrence of active ingredients in manure is demonstrated. It can be assumed that whenever veterinary medicinal products are used, portions of these will be found in the manure.

In some studies, a lot of samples were taken covering a large number of different manures—up to 380 samples

Table 1 List of categorized keywords

1 2 3 4 5 6

Manure Transfor- Veterinary Medicine Biocide Tetracycline

mation

Slurry Metabo- Drug Pesticide Sulfona-

lism mide

Feces Catabo- Pharma- Disinfect- Antibiotic

lism ceutical ant

Faeces Anabolism Antiparasitic

Lagoon Degrada-

Decompo-

sition

Dissipa-

Reaction

Conver-

Manage-

in Harms [25]—and in other studies only individual manures were sampled after medication. In 19 studies, only pig manure was analyzed, whereas three studies worked with cattle manure and four studies worked with pig, cattle, or poultry manure. One publication does not specify the origin of the analyzed manure.

Manure and liquid manure samples with different dry matter contents are considered in this literature study (range 0.2-44.4 %). Sixteen of 27 studies do not specify dry matter content as a basic parameter. Twelve of 27 studies report concentrations of substances in manure in mg/kg dry weight (dw), 10 of 27 studies work with mg/ kg wet weight (ww), and five studies do not specify (ns) whether they calculated concentrations on the basis of dry or wet weight. Because of this, it is difficult to compare the found concentrations of the single active substances. The lowest values are found at the |g/kg order of magnitude—often restricted by the limit of detection (LOD) of the analytical method.

Among all the reviewed literature, 39 different active substances of VMPs were found in manure. Moreover, 11 metabolites and transformation products of active substances were identified. For this, 1568 manure samples were analyzed within the 27 publications. Mainly, the samples were analyzed for sulfonamides, tetracyclines, and fluoroquinolones. None of the studies worked with a non-target approach or searched for biocides. By far, the most frequently found single active substances are sulfadimidine (599 positive), tetracycline (575 positive), and chlortetracycline (457 positive). There are six publications each of which analyzed more than 100 manure

samples. All of these are from Chinese or German institutes. The active substances with the highest percentage of positive findings (>50 %) within these six publications are chlortetracycline, oxytetracycline, tetracycline, and sulfadimidine.

The 15 highest concentrations were found in pig manure from Germany or China. The highest concentration was 1420.76 mg/kg (dw) of enrofloxacin, found in poultry manure from China, followed by 764.407 mg/ kg (dw) chlortetracycline in pig manure from China and 330.7 mg/kg (ww) in pig manure from Germany. Further, very high values were found for other sulfonamides, tet-racyclines, and fluorchinolones.

More recently, Berendsen et al. [10] developed a comprehensive method for the analysis of 44 antibiotic compounds in animal feces by liquid chromatogra-phy coupled with tandem mass spectrometry (LC-MS/ MS). As the study analyzed animal feces and not liquid manure, this study was not taken into account for Tables 2-5, although the measured VMPs will obviously end up in liquid manure. In 34 % of the samples, more than one antibiotic was detected.

Predicted environmental concentrations vs. measured environmental concentrations

With the summarized measured environmental concentrations (MECs) in Tables 2-5, it is possible to compare them with predicted environmental concentrations (PECs) in liquid manure as they are calculated for an environmental risk assessment of VMPs according to the EMA guidance [18]. With this analysis, the concept of PECs can be evaluated, since MECs are not relevant for the environmental risk assessment of VMPs. The guideline works with concentrations relating to the wet weight (mg/kg) and the nitrogen content of the manure, so that PECs in manure are given by

•ww manure —

D x Ad x Bw x Fh Ntotal — x

with PECww manure being the predicted environmental concentration in manure (mg/kgwet manure), D the daily dose of the active ingredient (mg/kgbw day), Ad the number of days of treatment (day), Bw the animal body weight (kgbw), Fh the fraction of herd treated (value between 0 and 1), Ns the nitrogen produced during storage time (kg N), and Ntotal the nitrogen content of the specific

manure (kg N/kgwet manure)'

The default values for Bw, Fh, and Ns are given within the EMA guideline [18], with respect to the type of animal (calf, dairy cow, cattle 0-1 year or >2 years, weaner pig, fattening pig, sow). Unfortunately, the exact animal type cannot often be deduced from the 27 publications, so that the simplified min./max. values of the term

Table 2 Sulfonamides and their metabolites and transformation products found in manure

Substance Reference Matrix Origin Min Max Unit Dry matter content, comments or quotation n n positive % positive

Sulfachloropyri- [28] Pig and poultry China 0.340 3.660 mg/kg (dw) "Liquid swine 6 2 33

dazine manure manure" (ns)

[79] Pig, cattle and poultry manure China 0.090 3.510 mg/kg (dw) (ns) 143 7 5

Sulfadiazine [20] Pig manure Germany (NI) 0.700 235.100 mg/kg (ww) 0.5-16.8 % (mean 5 %) 344 100 29

[23] Pig manure Germany 3.500 11.300 mg/kg (dw) 9.6-9.8 % 3 2 67

[25] Pig manure Germany (BY) 0.100 5.000 mg/kg (ww) 0.2-17.3 % (mean 3.7 %) 380 19 5

[28] Pig and poultry manure China 0.160 0.780 mg/kg (dw) "Liquid swine manure" (ns) 6 2 33

[31] Pig manure Denmark 0.630 2.100 mg/kg (dw) 2.8-13.4 % 6 2 33

[55] (ns) Germany 0.011 0.080 mg/kg (ns) "Liquid manure" (ns) 4 2 50

[56] Pig and cattle manure Germany (NW) - 0.650 mg/kg (dw) Liquid and stable manure (ns) 34 5 15

[77] Pig manure Germany 0.700 35.300 mg/kg (ww) 0.7-16.11 % 176 86 49

[79] Pig, cattle and poultry manure China 0.020 3.120 mg/kg (dw) (ns) 143 14 10

4-Hydroxy-sulfadi- [56] Pig and cattle Germany (NW) - 9.050 mg/kg (dw) Liquid and stable 34 8 24

azine manure manure (ns)

N4-Acetyl-sulfadi- [25] Pig manure Germany (BY) - - not quantified 0.2-17.3 % (mean 380 19 5

azine 3.7 %)

[55] (ns) Germany 0.010 0.270 mg/kg (ns) "Liquid manure" (ns) 4 2 50

[56] Pig and cattle manure Germany (NW) - 0.150 mg/kg (dw) Liquid and stable manure (ns) 34 6 18

Sulfadimethoxine [25] Pig manure Germany (BY) 0.050 0.600 mg/kg (ww) 0.2-17.3 % (mean 3.7 %) 380 5 1

[54] Pig manure China 0.120 1.255 mg/kg (dw) (ns) 126 3 2

Sulfadimidine [48] Pig manure Austria - <20 mg/kg (dw) "Liquid manure" (ns) 30 18 60

[8] Cattle manure Canada - 9.990 mg/kg (dw) 24.4-44.4 % (mean 37 %) 6 4 67

[13] Pig manure Switzerland 14.400 mg/L (ww) "In the supernatant" (water phase) (ns) 1 1 100

[15] Pig manure Germany 1.000 1.100 mg/kg (ww) (ns) 2 2 100

[15] Cattle manure Germany <0.1 <0.1 mg/kg (ww) (ns) 2 2 100

[20] Pig manure Germany (NI) 0.700 167.000 mg/kg (ww) 0.5-16.8 % (mean 5 %) 344 183 53

[23] Pig manure Germany - 7.200 mg/kg (dw) 9.6-9.8 % 3 1 33

[54] Pig manure China 0.011 28.700 mg/kg (dw) (ns) 126 65 52

[56] Pig and cattle manure Germany (NW) - 7.040 mg/kg (dw) Liquid and stable manure (ns) 34 6 18

[58] Pig manure Germany 0.130 20.000 mg/kg (dw) 1.2-28 % 30 18 60

[75] Pig manure Germany (BY) 0.140 1.700 mg/L (ww) 1-2 % 8 8 100

[77] Pig manure Germany 0.700 167.000 mg/kg (ww) 0.7-16.13 % 176 85 48

[79] Pig, cattle and poultry manure China 0.060 6.040 mg/kg (dw) (ns) 143 17 12

[22] Pig and cattle manure Switzerland 0.130 8.700 mg/kg (ww) 1.1-3.7 % 6 6 100

[25] Pig manure Germany (BY) 0.050 38.000 mg/kg (ww) 0.2-17.3 % (mean 3.7 %) 380 181 48

[55] (ns) Germany 0.011 0.062 mg/kg (ns) "Liquid manure" (ns) 4 2 50

Table 2 continued

Substance Reference Matrix Origin Min Max Unit Dry matter content, comments or quotation n n positive % positive

W4-Acetyl-sul- [22] Pig and cattle Switzerland <0.1 2.600 mg/kg (ww) 1.1-3.7 % 6 5 83

fadimidine manure

[25] Pig manure Germany (BY) 0.050 27.000 mg/kg (ww) 0.2-17.3 % (mean 3.7 %) 380 117 31

[75] Pig manure Germany (BY) 0.120 1.000 mg/L (ww) 1-2 % 8 8 100

Sulfadoxine [28] Pig and poultry manure China 0.350 0.710 mg/kg (dw) "Liquid swine manure" (ns) 6 3 50

[31] Pig manure Denmark 0.015 0.220 mg/kg (dw) 2.8-13.4 % 6 3 50

Sulfaguanidine [79] Pig, cattle and poultry manure China 0.010 1.550 mg/kg (dw) (ns) 143 27 19

Sulfamerazine [25] Pig manure Germany (BY) 0.700 0.900 mg/kg (ww) 0.2-17.3 % (mean 3.7 %) 380 7 2

[79] Pig, cattle and poultry manure China 0.090 0.660 mg/kg (dw) (ns) 143 6 4

W4-Acetyl-Sulfam- [25] Pig manure Germany (BY) - - not quantified 0.2-17.3 % (mean 380 5 1

erazine 3.7 %)

Sulfamethizole [54] Pig manure China 0.052 2.422 mg/kg (dw) (ns) 126 35 28

Sulfamethoxazole [25] Pig manure Germany (BY) 0.050 0.050 mg/kg (ww) 0.2-17.3 % (mean 3.7 %) 380 3 1

[28] Pig and poultry manure China 0.340 1.290 mg/kg (dw) "Liquid swine manure" (ns) 6 2 33

[51] Pig manure Japan 0.002 0.035 mg/kg (ns) (ns) 5 4 80

[51] Cattle manure after fermentation Japan 0.010 mg/kg (ns) (ns) 8 1 13

[54] Pig manure China 0.137 0.639 mg/kg (dw) (ns) 126 6 5

[58] Pig manure Germany <0.1 2.400 mg/kg (dw) 1.2-28 % 30 2 7

[79] Pig, cattle and poultry manure China 0.120 2.800 mg/kg (dw) (ns) 143 7 5

Sulfamethoxypyri- [56] Pig and cattle Germany (NW) - 0.020 mg/kg (dw) Liquid and stable 34 4 12

dazine manure manure (ns)

Sulfamonometh- [51] Pig manure Japan - 0.210 mg/kg (ns) (ns) 5 1 20

oxine [51] Cattle manure after fermentation Japan 0.022 mg/kg (ns) (ns) 8 1 13

[79] Pig, cattle and poultry manure China 0.060 4.080 mg/kg (dw) (ns) 143 39 27

Sulfanilamide [79] Pig, cattle and poultry manure China 0.020 1.590 mg/kg (dw) (ns) 143 5 3

Sulfaquinoxaline [56] Pig and cattle manure Germany (NW) - 0.670 mg/kg (dw) Liquid and stable manure (ns) 34 3 9

Sulfathiazole [22] Pig and cattle manure Switzerland 0.100 12.400 mg/kg (ww) 1.1-3.7 % 6 4 67

[25] Pig manure Germany (BY) 0.050 0.100 mg/kg (ww) 0.2-17.3 % (mean 3.7 %) 380 5 1

[54] Pig manure China 0.312 mg/kg (dw) (ns) 126 1 1

dwdry weight, ww wet weight, ns not specified

Bw/Ns of the whole species cattle or pig were used for the calculation of min./max. PECww manure values. For cattle, this results in minimum and maximum values of Bw/Ns of 28.33 and 56 kgbw/(kg N), respectively. For pigs, these values lie between 34.21 and 37.88 kgbw/(kg N).

The recommended daily doses (D) and the number of days of animal treatment (Ad) for specific products are given under point 4.9, in the summary of product characteristics (SPC). These parameters are, e.g., accessible via the product databases of the Veterinary Medicines

Directorate of the United Kingdom [71] or via the drug information portal of the German Federal Ministry of Health [12]. All registered VMPs containing the frequently found active ingredients such as chlortetracy-cline, oxytetracycline, tetracycline, sulfadimidine, and sulfadiazine were chosen for consideration of PECww manure values (oral or subcutaneous administration). For this, the minimum and maximum values of D x Ad were used for min./max. calculation of PECww manure (Table 6). The fraction of herd treated (Fh) was set to 1 [18].

Unfortunately, only very few of the monitoring studies report the nitrogen content of the analyzed manures. Additionally, the exact animal type is also very often not given within the 27 publications, as mentioned before. For this, minimum and maximum nitrogen contents of the different liquid manure types (Ntotal) were taken from secondary literature. Cattle liquid manure has a total nitrogen content between 3.2 and 4.7 g/L, whereas the nitrogen content of pig liquid manure ranges between 2.8 and 6.5 g/L [46]. For dry matter content below 25 %, a density of 1 g/mL can be assumed for liquid manure [7] so that nitrogen content can also be given as g/kg. PECdw manure values have not been calculated (dw: dry weight), as theoretical dry matter content of liquid manure is subject to a further high variability. Although the concentrations related to the dry weight of manure are generally more reliable than those given as wet weight concentrations.

The estimated PECsww manure are based on the total residue approach, i.e., metabolism of the VMPs was not taken into account. Moreover, it is concerning that for liquid manure from pigs, two publications reveal MECs of chlortetracycline, exceeding the highly conservative maximum PECww manure by a factor of two and five. Several further publications report MECsww manure for chlo-rtetracycline, which exceed the minimum PECww manure. Also for sulfadiazine one MECww manure exceeded the max. PECww manure. For sulfadimidine, tetracycline, and oxytetracycline, MECs are in the same order of magnitude as the calculated PECww manure. Considering injection products, the PECww manure is also exceeded by the highest MEC for oxytetracycline in Table 3.

Transformation of VMPs and biocides in liquid manure

The focus of this literature research was on transformation studies using liquid manure and manure from lagoons. Liquid manure is the substrate found in manure tanks, which consists of urine, feces, and sometimes bedding material and water from cleaning the stables. It is important to note the difference to dung or excrements, which are distinguished from manure by being directly excreted and not collected and stored for longer time periods during which anaerobic conditions develop [74].

In this review, also some studies using excrements and related matrices were included in order to get a comprehensive picture of available methods.

To study the environmental fate of VMPs, many different studies can be found, using mixtures of soil and manure or test systems containing additional plants. These are not considered for the survey. Studies on solid manure (mainly conducted at Asian institutions) are also not considered in this review as the composition of this material is considerably more variable than the composition of liquid manure, which results in e.g., wide ranges of oxygen availability. Compared to solid manure, liquid manure exhibits a more homogeneous composition. This type of manure was considered primarily, as it has been found to be the predominant type of manure in the EU countries and North America [74]. Generally, the research on the transformation of pharmaceuticals in manure focuses on North America, Europe, and Asia. There are some studies working on manure treatment technologies and some studies working on the effects of VMPs on biogas production without studying transformation. Those studies are also not considered here.

A limited number of 42 relevant studies dealing with the transformation of VMPs and biocides in liquid manure could be found. These studies are assorted in Tables 7 and 8, together with information on their experimental design. On the whole, there are only scarce data on the transformation of veterinary medicinal products. Especially on the transformation of biocides only three publications were found. However, there is an increasing publication rate worldwide, which reflects the interest in and relevance of this research field.

Citation map

The following citation map (Fig. 1) provides a visualization of the interconnection of the authors/working groups by generating a network and visualizing their respective impact in this field of research. Each node represents one publication. The darker and the bigger the node, the more often the publication is cited. The arrows show who cites whom, and their thicknesses correlate with the citation flow indicating established thematic clusters. Only three publications are completely left out citing each other, owed to dealing with hormones and lagoon water. One isolated work of Varel [67] considers deliberate application of (natural) biocides to manure. This was to stop microbial activity and prevent "odor emissions" during the storage of manure. One cluster is implied on the left of this network, showing all the seven publications, which used 14C-labeled compounds, all originating from Germany (working groups Kreuzig and Spiteller). The most often cited publications within the community network of the 42 papers are from Arikan

Table 3 Tetracyclines and their metabolites and transformation products found in manure

Substance Reference Matrix Origin Min Max Unit Dry matter content, comments or quotation n n positive % positive

Chlortetracy- [48] Pig manure Austria 0.100 46.000 mg/kg (dw) "Liquid manure" (ns) 30 17 57

cline [20] Pig manure Germany (NI) 1.100 330.700 mg/kg (ww) 0.5-16.8 % (mean 5 %) 344 44 13

[24] Pig manure Germany 0.090 0.100 mg/kg (ww) (ns) 2 2 100

[23] Pig manure Germany 0.900 1.000 mg/kg (dw) 9.6-9.8 % 3 2 67

[25] Pig manure Germany (BY) 0.100 50.800 mg/kg (ww) 0.2-17.3 % (mean 3.7 %) 380 140 37

[28] Pig and poultry manure China 0.150 14.700 mg/kg (dw) "Liquid swine manure" (ns) 6 4 67

[31] Pig manure Denmark 1.100 15.700 mg/kg (dw) 2.8-13.4 % 6 5 83

[51] Pig manure Japan 0.240 0.280 mg/kg (ns) (ns) 5 2 40

[51] Cattle manure after fermentation Japan - 0.001 mg/kg (ns) (ns) 8 1 13

[54] Pig manure China 0.053 764.407 mg/kg (dw) (ns) 126 122 97

[56] Pig and cattle manure Germany (NW) - 3.600 mg/kg (dw) Liquid and stable manure (ns) 34 7 21

[58] Pig manure Germany 0.100 46.000 mg/kg (dw) 1.2-28 % 30 17 57

[66] Pig manure Czech Republic - 5.880 mg/kg (ns) "Liquid hog manure" (ns) 5 1 20

[75] Pig manure Germany (BY) 0.600 2.000 mg/L (ww) 1-2 % 3 3 100

[77] Pig manure Germany 1.100 25.700 mg/kg (ww) 0.7-16.1 % 176 18 10

[79] Pig, cattle and poultry manure China 0.160 27.590 mg/kg (dw) (ns) 143 72 50

Epi-chlortetra- [31] Pig manure Denmark 1.700 14.100 mg/kg (dw) 2.8-13.4 % 6 5 83

cycline

Doxycycline [25] Pig manure Germany (BY) 0.100 0.700 mg/kg (ww) 0.2-17.3 % (mean 3.7 %) 380 5 1

[31] Pig manure Denmark 0.550 3.100 mg/kg (dw) 2.8-13.4 % 6 6 100

[66] Pig manure Czech Republic - 0.990 mg/kg (ns) "Liquid hog manure" (ns) 5 1 20

[79] Pig, cattle and poultry manure China 0.230 13.500 mg/kg (dw) (ns) 143 21 15

Metacycline [79] Pig, cattle and poultry manure China 0.140 5.860 mg/kg (dw) (ns) 143 50 35

Oxytetracycline [48] Pig manure Austria 0.290 29.000 mg/kg (dw) "Liquid manure" (ns) 30 22 73

[43] Cattle manure Italy - 19.000 mg/kg (ns) "Heap" (ns) 1 1 100

[20] Pig manure Germany (NI) 1.600 136.200 mg/kg (ww) 0.5-16.8 % (mean 5 %) 344 10 3

[25] Pig manure Germany (BY) 0.100 0.900 mg/kg (ww) 0.2-17.3 % (mean 3.7 %) 380 16 4

[31] Pig manure Denmark 0.048 1.500 mg/kg (dw) 2.8-13.4 % 6 3 50

[51] Pig manure Japan - 0.013 mg/kg (ns) (ns) 5 1 20

[51] Cattle manure after fermentation Japan - 0.001 mg/kg (ns) (ns) 8 1 13

[54] Pig manure China 0.044 172.874 mg/kg (dw) (ns) 126 114 90

[56] Pig and cattle manure Germany (NW) - 1.490 mg/kg (dw) Liquid and stable manure (ns) 34 5 15

[58] Pig manure Germany 0.210 29.000 mg/kg (dw) 1.2-28 % 30 22 73

[77] Pig manure Germany 1.600 136.200 mg/kg (ww) 0.7-16.9 % 176 9 5

[79] Pig, cattle and poultry manure China 0.150 59.590 mg/kg (dw) (ns) 143 50 35

[33] Cattle manure Turkey - 0.060 mg/kg (ns) (ns) 1 1 100

Table 3 continued

Substance Reference Matrix Origin Min Max Unit Dry matter content, comments or quotation n n positive % positive

Epi-oxytetracy-cline [31] Pig manure Denmark 0.330 0.450 mg/kg (dw) 2.8-13.4 % 6 2 33

Tetracycline [48] Pig manure Austria 0.360 23.000 mg/kg (dw) "Liquid manure" (ns) 30 22 73

[24] Pig manure Germany 3.200 4.000 mg/kg (ww) (ns) 2 2 100

[23] Pig manure Germany 14.100 41.200 mg/kg (dw) 9.6-9.8 % 3 3 100

[25] Pig manure Germany (BY) 0.100 46.000 mg/kg (ww) 0.2-17.3 % (mean 3.7 %) 380 111 29

[28] Pig and poultry manure China 0.180 0.840 mg/kg (dw) "Liquid swine manure" (ns) 6 4 67

[31] Pig manure Denmark 0.091 1.600 mg/kg (dw) 2.8-13.4 % 6 5 83

[51] Pig manure Japan 0.005 0.015 mg/kg (ns) (ns) 5 3 60

[51] Cattle manure after fermentation Japan - 0.001 mg/kg (ns) (ns) 8 2 25

[54] Pig manure China 0.037 19.417 mg/kg (dw) (ns) 126 107 85

[56] Pig and cattle manure Germany (NW) - 2.450 mg/kg (dw) Liquid and stable manure (ns) 34 12 35

[58] Pig manure Germany 0.360 23.000 mg/kg (dw) 1.2-28 % 30 22 73

[78] Pig manure Germany (NW) 0.600 66.000 mg/L (ww) "Pig slurry" (ns) 181 43 24

[77] Pig manure Germany 0.900 43.100 mg/kg (ww) 0.7-16.8 % 176 87 49

[20] Pig manure Germany (NI) 0.700 45.700 mg/kg (ww) 0.5-16.8 % (mean 5 %) 344 152 44

Epi-tetracycline [31] Pig manure Denmark 0.061 0.990 mg/kg (dw) 2.8-13.4 % 6 5 83

dwdry weight, ww wet weight, ns not specified

et al. [6], Kolz et al. [34], Kühne et al. [40], Loke et al. [44], and Winckler and Grafe [78]. This is partly explainable by the relatively early dating of these publications.

Studied substance classes

Equivalent to the application practice in livestock breeding, mainly tetracyclines (20 of 42 studies), sulfonamides (12 of 42 studies), and macrolides (10 of 42 studies) are considered. There are only a few studies with parasiticides. For biocides, only three publications were found [35, 37, 67]. Within 2 of 42 studies, transformation of excreted hormones was investigated. Although they are not about VMPs, these publications are also considered because they are well documented (e.g., measured redox potential) and conducted similar to transformation studies with VMPs.

Chemical analysis

As already mentioned with regard to the citation map, seven studies used 14C-labeled test substances. By this, a mass balance of the experiment considering transformation, mineralization, volatilization, and the formation of non-extractable residues is possible. The methods used

are radio thin-layer chromatography (RTLC), oxidizers for solid samples, and liquid scintillation counting (LSC). Only Heuer et al. [26] and Lamshoft et al. [41] further used LC-MS techniques in combination with radio techniques, an approach that will be inevitable in future studies to gain maximum information out of transformation studies in terms of transformation product identification and quantification.

Most of the studies worked with unlabeled substances and used LC-MS/MS for detection and quantification of the VMPs and biocides and their transformation products (24 publications). Some of them combined UV-Vis/diode array detector (DAD) methods with MS methods (4 publications). For example, Schlusener et al. [59] used HR-MS (high-resolution mass spectrom-etry) for further salinomycin transformation product identification. Within nine publications, only UV-Vis/ DAD detection methods were used. The GC (gas chromatography) method was applied only by Varel [67] for the detection of the terpenoids carvacrol and thymol. Additionally, Varel et al. [68] applied an ELISA method (enzyme-linked immunosorbent assay) for the detection of chlortetracycline.

Table 4 Fluorchinolones found in manure

Substance Reference Matrix Origin Min Max Unit Dry matter content, comments or quotation n n positive % positive

Ciprofloxa- [51] Pig manure Japan - 0.006 mg/kg (ns) (ns) 5 1 20

cin [51] Cattle manure after fermentation Japan 0.002 0.012 mg/kg (ns) (ns) 8 4 50

[56] Pig and cattle manure Germany (NW) - 0.070 mg/kg (dw) Liquid and stable manure (ns) 34 3 9

[58] Pig manure Germany 0.180 0.620 mg/kg (dw) 1.2-28 % 30 4 13

[75] Pig manure Germany (BY) 0.005 0.028 mg/L (ww) 1-2 % 5 5 100

[79] Pig, cattle and poultry manure China 0.490 45.590 mg/kg (dw) (ns) 143 44 31

Danofloxa-cin [56] Pig and cattle manure Germany (NW) 0.050 mg/kg (dw) Liquid and stable manure (ns) 34 1 3

[79] Pig, cattle and poultry manure China 0.080 3.060 mg/kg (dw) (ns) 143 39 27

Difloxacin [79] Pig, cattle and poultry manure China 0.410 12.380 mg/kg (dw) (ns) 143 8 6

Enrofloxa- [48] Pig manure Austria 0.130 0.750 mg/kg (dw) "Liquid manure" (ns) - - -

cin [56] Pig and cattle manure Germany (NW) 0.550 mg/kg (dw) Liquid and stable manure (ns) 34 5 15

[58] Pig manure Germany 0.130 0.750 mg/kg (dw) 1.2-28 % 30 5 17

[75] Pig manure Germany (BY) 0.050 0.116 mg/L (ww) 1-2 % 5 5 100

[79] Pig, cattle and poultry manure China 0.330 1420.760 mg/kg (dw) (ns) 143 67 47

Fleroxacin [79] Pig, cattle and poultry manure China 0.760 99.430 mg/kg (dw) (ns) 143 35 24

Levofloxa- [51] Pig manure Japan - 0.003 mg/kg (ns) (ns) 5 1 20

cin [51] Cattle manure after fermentation Japan 0.001 0.002 mg/kg (ns) (ns) 8 2 25

Lome-floxacin [79] Pig, cattle and poultry manure China 0.610 44.160 mg/kg (dw) (ns) 143 45 31

Marbo-floxacin [56] Pig and cattle manure Germany (NW) - 0.050 mg/kg (dw) Liquid and stable manure (ns) 34 3 9

Norfloxa-cin [79] Pig, cattle and poultry manure China 0.560 225.450 mg/kg (dw) (ns) 143 37 26

Ofloxacin [28] Pig and poultry manure China 0.450 3.870 mg/kg (dw) "Liquid swine manure" (ns) 6 2 33

Orbifloxa-cin [56] Pig and cattle manure Germany (NW) - 0.020 mg/kg (dw) Liquid and stable manure (ns) 34 1 3

Sarafloxa-cin [56] Pig and cattle manure Germany (NW) - 0.060 mg/kg (dw) Liquid and stable manure (ns) 34 1 3

dwdry weight, ww wet weight, ns not specified

Metabolites and transformation products

With regard to VMPs, it is important to distinguish between metabolites, which may be formed in the treated animal, and transformation products, which may be formed from excreted parent compounds and metabolites in the environment.

Transformation products or metabolites were determined in 26 studies. This implies sophisticated methodology by liquid chromatography coupled to

preferably tandem mass spectrometry or high-resolution mass spectrometry (LC-MS/MS or LC-HR-MS). For specific applications, HPLC (high-performance liquid chromatography) with UV (ultraviolet) detection may be sufficient [78]. Due to missing reference substances, transformation products are often determined only qualitatively.

For example, Arikan [5] studied in detail the fate of chlortetracycline (CTC) during anaerobic digestion of

Table 5 Other veterinary medicines and its metabolites and transformation products found in manure

Substance Reference Matrix Origin Min Max Unit Dry matter content, n n posi- % posi-

comments tive tive

or quotation

Flubendazole [75]

Amino-fluben- [75]

dazole

Hydroxy- [75]

flubendazole

Lincomycin [39]

Salinomycin [60] Spectinomycin [39]

Tiamulin [25]

[54] [60] [53]

[43] [63] [75]

Toltrazuril

Toltrazuril sulfone Toltrazuril sulfoxide Trimethoprim

Tylosin

Pig manure

Pig manure

Pig manure

Pig manure Pig manure Pig manure Pig manure

Pig manure Pig manure Pig manure

Pig manure

Pig manure

Germany

(BY) Germany

(BY) Germany

(BY) Canada Germany Canada Germany

(BY) China Germany Denmark

Denmark

Denmark

Pig and cattle Switzerland <0.1 manure

Pig and cattle Germany -manure (NW)

Cattle manure Italy -

Pig manure Canada 0.030

0.020 0.056 mg/L (ww)

0.032 0.110 mg/L (ww)

0.018 0.075 mg/L (ww)

2.520 9.780 mg/L (ww)

- 0.011 mg/kg (ns) 0.173 0.686 mg/L (ww)

- 0.500 mg/kg (ww)

0.076 0.169 mg/kg (dw)

- 0.043 mg/kg (ns)

- 0.114 mg/kg (dw)

- 0.085 mg/kg (dw)

- 0.007 mg/kg (dw) <0.1 mg/kg (ww)

0.050 mg/kg (dw)

<0.25 0.543

mg/kg (ns) mg/kg (dw)

Pig manure

Germany (BY)

0.130 0.320 mg/L (ww)

1-2 % 7

1-2 % 7

1-2 % 7

mean 2.4 % 5

mean 2.4 % 5

0.2-17.3 % 380

(mean 3.7 %)

(ns) 126

"Manure from a slurry 1

storage tank" (ns)

"Manure from a slurry 1

storage tank" (ns)

"Manure from a slurry 1

storage tank" (ns)

1.1-3.7 % 6

Liquid and stable 34 manure (ns)

"Heap" (ns) 1

(ns) - -

1-2 % 8 8

100 25 100 <1

25 100

dw dry weight, ww wet weight, ns not specified

manure from medicated calves. The CTC concentration decreased about 75 % and the concentration of the CTC epimer, 4-epi-chlortetracycline, declined roughly 33 % during the 33-day experiment. The CTC metabolite iso-chlortetracycline increased twofold in concentration. Referring to a higher water solubility, the authors concluded a possible occurrence of metabolites of CTC in water bodies. Also Mitchell et al. [49] stated that solid and liquid effluents from anaerobic digestion treatment containing antibiotic transformation products could represent an environmental concern.

For example, in the study by Heuer et al. [26], the concentration of sulfadiazine (SDZ) increased by 42 % during the storage of manure due to deacetylation of the metabolite A-acetyl-SDZ. Basically, the same was determined by Lamshoft et al. [41] who state that environmental effects may be underestimated, if the parent compound alone was considered for the environmental risk assessment.

Source of manure

There are different approaches on the application of the test substance to manure in respect of transformation studies. Contaminated manure can be obtained by sampling a tank containing the manure from previously medicated animals. If metabolites are of concern, a more realistic scenario can thus be studied. The deacetylation of the metabolite A-acetyl-sulfadiazine in manure, after excretion back to the parent compound sulfadiazine, is a well-studied example [26, 41]. Further, VMPs influence the microbial community structure and thus its own transformation fate in manure. The same applies to the effect of biocides on microbial community. Considering analytical method development, using medicated manure makes it difficult if not impossible to determine the recovery rates of the analytes out of the excreted and then aged manure. At this point, only radioactive methods can provide a valid survey on parent compound excretion and distribution. In the literature under study,

Table 6 Predicted environmental concentrations and measured environmental concentrations in manure as given in Tables 2-5 (PECww manure and MECww manure) of the five most frequently monitored and found VMPs in (liquid) manure

Active ingredient (number of registered products considered) Species Min.-max. PECww manure (mg/kgww) Highest MECsww manure (mg/kgww)

Chlortetracycline (19) Cattle 10.9-24.9 -

Pig 4.0-154.7 330.7, 764.4

Oxytetracycline (30) Cattle 0.49-44.5 -

Pig 0.48-182 136.2

Tetracycline (8) Cattle 10.9-72.8 -

Pig 31.7-216.6 66.0

Sulfadimidine (19) Cattle 4.4-124.6 -

Pig 3.2-254.8 167.0

Sulfadiazine (21) Cattle 1.6-22.3 -

Pig 1.0-45.5 235.1

Among the MECsww manure, only those for which the concentrations in liquid manure were clearly given as mg/kgwet weight were considered MECsww manure exceeding the max. PECww manure are italicized

only Heuer et al. [26] and Lamshoft et al. [41] worked with radioactive labeled VMPs and medicated manure (14C-sulfadiazine, 14C-difloxacin). Overall, 16 out of 42 studies were conducted with medicated manure. Additionally, three studies worked with both medicated and spiked manure [29, 72, 73].

In general, spiking manure in laboratory scale is a much more reproducible way of generating contaminated manure and the only way to conduct transformation studies of biocides. By this approach, it is possible to determine recovery rates with unlabeled compounds and to study sorption processes. Nevertheless, Huang et al. [29] report that methane production of manure spiked with chlortetracycline (0.55 mg/kg dw) was reduced by 12 % compared to manure of treated animals with the same chlortetracycline concentration. Further, Wang et al. [72] found a lower diversity index of methanogenic archaea in manure of animals treated with tylosin compared to manure spiked with tylosin at the same concentration. Wang et al. [73] also found differences between spiked manure and manure from treated animals in terms of the abundance of oxytetracycline-degrading Bacillus cereus and transformation products of oxytetracycline.

Generally, liquid manure is an anaerobic liquid medium. Samplings taken directly from a tank at a farm represent the most reliable source of liquid manure. By this approach, a microbial community, typical for authentic storage tanks, is used in the transformation experiment, which is not the case if excrements are sampled from diverse animals and mixed afterwards in order to obtain a manure-like medium. Ten out of 42 studies worked with liquid manure taken out of a bigger tank at a farm. In contrast to this, 22 publications report a procedure of mixing more or less fresh excrements with

water and in some cases with an inoculum to produce liquid manure on a laboratory scale. Out of these 22, only Varel et al. [68] describe a well-documented procedure of generating a "seed manure" over a time period of 2-5 months to then mix it with fresh manure in order to preserve a reproducible artificial liquid manure.

Four studies worked with lagoon water, which mainly differs from liquid manure in its lower dry matter content of 1.2-3.6 %. Additionally, Li et al. [42] used "recycled water derived from a beef farm." Within one publication, lagoon sediment was mixed with water down to a dry matter content of 2.7 % [2]. Cetecioglu et al. [14] and Angenent et al. [4] took manure for transformation experiments out of a continuously running anaerobic sequencing batch reactor (ASBR), whereas Mohring et al. [50] and Riemenschneider et al. [57] took it directly out of a biogas plant.

Matrix characteristics and sorption to suspended solids

From the 42 studies under investigation, 10 used cattle manure featuring dry matter contents from 1.1 up to 15 %. Three studies used both pig and cattle manure. One study relied on a synthetic matrix-water mixture-including volatile fatty acids, glucose, and starch—to approximate properties of liquid manure [14]. Within the remaining 28 studies, pig manure with dry matter contents from 2 up to 22 % was used. Comparing the results is complicated due to the differing dry matter contents. Kreuzig [35] emphasizes substance-specific interactions with the different pig or cattle manure matrices. He further mentions that the dry substance content of manure can be one of the most relevant factors affecting the transformation of VMPs and biocides. In a study on the stability of tylosin A in manure, Loke et al. [44] could

Table 7 Studies on the transformation of VMPs and biocides in liquid manure and similar matrices (excrements, biosol-ids, etc., as specified in the second last column)

Author (Year) Substances Substance TP Initial concentration DT50 Miner- Manure Dry

class aliza- (type and source) matter

Akyol et al. Oxytetracy- Tetracycline + 1.51-2.57 mg/L 13-17 days nd Cattle (medicated, 4.0, 5.5 %

(2016) [1] cline mixed excrements)

Ali et al. (2013) Tylosin Macrolide - 160 mg/L nd (highly pH and nd Cattle (spiked, mixed 2.7 %

[2] Eh dependant) lagoon sediment)

Alvarez et al. Oxytetracy- Tetracycline + 10, 50, 100 mg/L 15.4-12.0 (OTC), nd Pig (spiked, tank) nd

(2010) [3] cline (OTC), 4.1-3.2 (CTC)

Chlortet- days

racycline

Angenent et al. Tylosin A Macrolide + 5.8 mg/L (measured) 2.49 h nd Pig (spiked, tank/ASBR) nd

(2008) [4]

Arikan (2008) Chlortetracy- Tetracycline + 1.0 and 5.9 mg/L 18 days nd Pig (medicated, mixed 5 %

[5] cline (buffer extraction, excrements)

Arikan et al. Oxytetracy- Tetracycline + 9.8 mg/L 56 days nd Cattle (medicated, 5 %

(2006) [6] cline mixed excrements)

Bailey et al. Sulfadiazine, Sulfona- - Each 10 mg/L nd nd Cattle (medicated, 5, 10, 15 %

(2016) [9] sulfadimi- mide, mixed excrements)

dine, tetracy-

sulfameth- cline

oxazole,

tetracycline

Blackwell et al. Oxytetracy- Tetracycline, - 19.2 (OTC), 26.1 (SCP) 79 (OTC), 127 nd Pig (spiked, tank) 2 %

(2005) [11] cline (OTC), sulfona- mg/L (SCP) days

sulfachloro- mide

pyridazine

Cetecioglu Tetracycline Tetracycline - Gradient: 1.65, 5.7, nd nd Synthetic (spiked, ASBR) nd

et al. (2013) 8.5 mg/L

Grote et al. Chlortetracy- Tetracycline, + Up to: 87.5 (CTC), nd nd Pig (medicated, "barrels") nd

(2004) [21] cline (CTC), sulfona- 498.9 (SDZ), 15.8

sulfadiazine mide (TMP) mg/kg

(SDZ), tri-

methoprim

Harms (2006) 20 different Tetracycline, - Numerous, many not nd nd Pig (medicated and nd

[25] substances sulfona- given spiked, tank)

mide, and

others

Heuer et al. Sulfadiazine Sulfona- + >80 mg/kg nd (DT50 not <1 % Pig (medicated, mixed 6 %

(2008) [26] (14C) mide reached) excrements)

Holtge and Sulfameth- Sulfona- + 3 mg/kg nd <1 % Cattle (spiked, mixed 13 %

Kreuzig oxazole, mide and excrements)

(2007) [27] acetyl-sul- metabo-

famethox- lite

azole (each

Huang et al. Chlortetracy- Tetracycline - 0.55 mg/g nd nd Pig (medicated, spiked, nd

(2014) [29] cline mixed excrements)

Joy et al. (2014) Bacitracin Polypeptide + 50 (BAC), 300 (CTC), 1.9 (BAC), 1 (CTC), nd Pig (medicated, mixed 0.84(BAC),

[32] (BAC), chlo- antibiotic, 10 (TYL) mg/kg 9.7 (TYL) d excrements) 0.37(CTC),

rtetracycline tetra- 0.89(TYL)

(CTC), tylo- cycline, %

sin (TYL) macrolide

Kolz et al. Tylosin Macrolide + 20 and 195 mg/L DT90: 40-500 h nd Pig (spiked, lagoon 1.5, 3.6 %

(2005) [34] water)

Table 7 continued

Author (Year) Substances

Substance TP class

Initial concentration DT5

Miner- Manure Dry

aliza- (type and source) matter tion

Kreuzig (2010) [35]

Kreuzig and Höltge (2005) [38]

Kreuzig et al. (2007) [36]

Kreuzig et al.

(2010) [37] Kuchta and Cessna

(2009) [39]

Kühne et al.

(2000) [40] Lamshöft et al.

(2010) [41]

Li et al. (2011) [42]

Loke et al.

(2003) [45] Loke et al.

(2000) [44] Mitchell et al. (2013) [49]

Mohring et al.

(2009) [50] Riemenschneider et al. (2014) [57]

Schlüsener et al. (2006) [59]

Erythromycin (ERY), sulfamethoxazole (SMZ), cyanamidea (CYN), imazalila (IMZ), (each 14C)

Sulfadiazine

Fenbenda-zole (FEN), flubenda-zole (FLU), (each 14C)

Imazalila (14C)

Lincomycin (LIN), spec-tinomycin (SPN)

Tetracycline

Difloxacin (DIF),

sulfadiazine (SDZ), (each 14C)

Ceftiofur

Oxytetracy-

cline Tylosin A

Ampicillin, florfenicol, sulfadimi-dine, tylosin

8 Sulfona-

mides Colistin

Macrolide, -sul-

fonamide,

biocide,

imidazole

Sulfona- -mide

Benzimida- + zole

Imidazole +

Antimicro- -bial

Tetracycline +

Fluoroqui- +

nolone, sulfona-mide

ß-Lactam + antibiotic

Tetracycline +

Macrolide +

ß-Lactam + antibiotic, ampheni-col, sulfonamide, macrolide Sulfona- +

mide Polypeptide -antibiotic

Erythromycin, Macrolide, +

roxithro-mycin, salinomycin, tiamulin

iono-phore, pleuro-mutilin

Only absolute nd

radioactivity given; 0.1-0.2 MBq

500 Mg/kg

17 days

200 (FEN), 2500 (FLU) nd (DT50 not Mg/kg reached)

4.3 and 4.5 mg/kg >177 days

38.7 (LIN), 387 (SPN) nd Mg/L

200 mg/L

17.1 ± 0.4 (DIF), 156.0 ± 4.2 (SDZ) mg/L

19.1 Mmol/L

2 and 30 mg/L 5 mg/L

9 days

nd (DT50 not reached)

<2 days

Each 0.001-1.0 mM/L nd

2-14 mg/kg 1, 2, 5, 500 mg/kg

2 mg/kg

6->180 days

<0.1 % Pig, cattle (spiked, mixed 2.5, 5, 10 % (ERY, excrements) SMZ); 28 % (CYN); nd for (IMZ)

1 % Cattle (spiked, mixed 13 %

excrements)

<0.6 % Pig (spiked, mixed excre- 3-13 % ments)

0.1 % Pig, cattle (spiked, mixed 2.5, 5, 10 %

excrements)

nd Pig (spiked, lagoon nd

water)

1.7-41 (highly dependant on T and dilution ratio with water) nd nd

0.2 % (DIF), 0.5 % (SDZ)

Pig (spiked, tank)

Pig (medicated, mixed 3.3-6 % excrements)

Cattle (spiked, "water 1.1 % from farm")

Pig (spiked, tank) nd

Pig (spiked, tank) nd

Cattle (spiked, mixed 3-6 % excrements)

Pig (spiked, biogas 15.2 % plant)

Pig and cattle (spiked, 3-4 % biogas plant)

Pig (spiked, tank)

Table 7 continued

Author (Year) Substances Substance class TP Initial concentration DT50 Mineraliza-tion Manure (type and source) Dry matter

Shelver and Varel (2012) [61] Chlortetracycline Tetracycline + >100 and >300 ng/L (only given in figures) >21 days at 22 °C, <5 days at 38 and 55 °C nd Pig (medicated, mixed excrements) nd

Shi et al. (2011) [62] Tetracycline, sulfamethoxydiazine Tetracycline, sulfona-mide Each 25 and 50 mg/L <12 h nd Pig (spiked, mixed excrements) 10 %

Stone et al. (2009) [64] Chlortetracycline (CTC), tylosin (TYL) Tetracycline, macrolide + 28 (CTC), 1.1 (TYL) mg/L nd nd Pig (medicated, manure) nd

Szatmari et al. (2011) [65] Doxycycline Tetracycline - 61.57 ± 14.26 mg/kg 53 days nd Pig (medicated, manure) nd

Varel (2002) [67] Carvacrola, thymola Terpenoid - Each 6.716.75 mmol/L nd nd Pig (spiked, mixed excrements) nd

Varel et al. (2012) [68] Chlortetracycline (CTC), monensin (MON) Tetracycline, iono-phores 5.9-8.3 (CTC), 0.3-0.74 (MON) mg/L nd (DT50 not reached for MON) nd Pig, cattle (medicated, seed slurry and manure) 4 %

Wang et al. (2014) [72] Tylosin Macrolide - 12 mg/kg nd nd Pig (medicated, spiked, mixed excrements) nd

Wang et al. (2015) [73] Oxytetracy-cline Tetracycline + 3746.39 mg/kg 9.04 and 9.65 days nd Pig (medicated, spiked, mixed excrements) 22 %

Widyasari-Mehta et al. (2016) [76] Doxycycline Tetracycline + 51 and 20 mg/kg 120 and 91 days nd Pig (spiked, tank, biogas plant) 1.8 %

Winckler and Grafe (2001) [78] Tetracycline Tetracycline 20 and 100 mg/L 55-105 days nd Pig (spiked, tank) nd

Zheng et al. (2012) [80] 17-ß-Estradiol, Hormone 17-a-estradiol, estrone + Each 5 mg/L nd nd Cattle (spiked, lagoon water) nd

Zheng et al. (2013) [81] 17a-Estradiol-3-sulfate Conjugate of a hormone + 5 mg/L 23-724 days nd Cattle (spiked, lagoon water) 1.2 %

TP transformation products considered, nd not determined or not defined, DT50 disappearance time 50 %

a Biocides

not clarify whether the decrease in the concentration of this compound is caused by sorption or abiotic or biotic chemical degradation. Similarly, Shi et al. [62] could not explain whether the rapid disappearance of the investigated antibiotics tetracycline and sulfamethoxydiazine could be due to their adsorption onto solid materials or degradation by microorganisms. In another study, Loke et al. [45] stated that very low free concentrations of oxy-tetracycline and metabolites in an anaerobic degradation experiment are due to the high amounts of substances being bound to particles in the manure matrix rather than to the degradation to unknown compounds.

In 17 studies, this dry matter content, which is strongly influencing sorption of the test substances, is not even mentioned and thus prohibiting a deeper interpretation of the results. Dry matter content is a key parameter, which impacts the dissipation rates, as shown by Alvarez et al. [3], Arikan [5], Kolz et al. [34], Kreuzig [35], and Kuchta

et al. [39]. These authors investigated explicitly sorption onto solid matter, which had already been recognized as a crucial parameter by Winckler and Grafe [78].

Experimental setup

A wide variety of experimental setups were used in the different studies analyzed. The amount of manure used for one replicate ranges from 1 mL [4] up to 295 L [78]. By far, most of the studies were conducted with 50-500 mL manure. Ten studies do not report a clearly defined amount of manure used. Most studies seem to have been conducted without any agitation of the manure during the experiments or they do not clearly report it. There are only a few studies, which mention a periodical stirring of the test manure or at least a stirring directly before sampling the manure.

Some studies refer to several guidelines. Loke et al. [44, 45] refer to ISO 11734 [30], Mohring et al. [50] refer to

Table 8 Studies on the transformation of VMPs and biocides in liquid manure

Author (Year) Focus Setup Amount of manure Precondition- Repli- Study-r Eh (mV) Study

and param- ing/acclimati- cates (°C) duration

eters zation (days)

Akyol et al. Biogas produc- 1-L batch digesters 600 mL + 60 mL nd 1 + con- 55 nd 20

(2016) [1] tion, abundance of bacteria (log copy number/100 ng cDNA) continuously stirred inoculum from laboratory digester trol

Ali et al. (2013) pH and Eh 2.3-L erlenmeyer flask, 150 g wet lagoon sedi- 1 week for 1 25 (-100), 20

[2] continuously stirred ment + 1.5 L 0.01 M stabilization of (0), (250),

and flushed with CaCl2 pH and Eh (350)

N2/O2 for different

Eh (Fig. 5)

Älvarez et al. Biogas com- 500-mL glass flasks 385 mL + inoculum Basal medium: 2 35 nd 21

(2010) [3] position, pressure, sorption with coiled butyl rubber stoppers (granular biomass from an anaerobic internal circulation digester) cysteine (0.5 g/L), NaHCO3 (5 g/L), pH 7.07.2; flushing with N2, 1.2 mL Na2S (20 g/L) (reducing agent)

Angenent Antibiotic Manure taken from 1 mL 249 days of ASBR 1 25 nd 2

et al. (2008) resistance, ASBR effluent, 5-mL operation

[4] methane production, volatile solids removal, VFA capped glass serum vials

Arikan (2008) Sorption, pH, 1-L batch laboratory 800 mL nd 3 35 nd 33

[5] total solids, volatile solids, total alkalinity, nh4-n, COD digester manure + 200 mL inoculum from a dairy manure digester

Arikan et al. Biogas produc- 1.225-L batch labora- 1 L manure + 225 mL nd 3 35 nd 64

(2006) [6] tion, total solids, total alkalinity, total N, total P tory digester inoculum from a dairy manure digester

Bailey et al. liquid-solid 15-mL polypropylene 3.3-10 g 14 days at 23 °C 3 23 nd 28

(2016) [9] distribution (Kd) centrifuge tubes

Blackwell et al. Exposure Closed bottle test, 200 mL nd 3 20 nd 40

(2005) [11] assessment, organic carbon, dry matter, available P and N tightly capped and stored without agitation

Cetecioglu Synthetic ASBR, concentration 1 L 150 days of ASBR 1 35 nd 155

et al. (2013) manure, influent and efflu- operation

[14] COD, biogas production ent, sludge

Grote et al. Metabolism, Outdoor realistic "Barrels" nd 1 Outdoor nd 240 + 210

(2004) [21] transformation conditions with continuous influent of contaminated manure

Table 8 continued

Author (Year) Focus

and parameters

Amount of manure

Preconditioning/acclimatization

Replicates

Study-r Eh (mV) (°C)

duration

(days)

Harms (2006) [25]

Heuer et al. (2008) [26]

Transformation nd

Bacterial community

Hôltge and Transforma- 300-mL flasks, glass 50 g

Kreuzig (2007) [27]

Huang et al. (2014) [29]

Joy et al. (2014) [32]

Kolz et al. (2005) [34]

Kreuzig (2010) [35]

Kreuzig and Höltge (2005) [38]

Kreuzig et al. (2007) [36]

Kreuzig et al. (2010) [37]

Kuchta and

Cessna (2009) [39]

Kühne et al.

(2000) [40] Lamshöft et al. (2010) [41]

Li et al. (2011) [42]

tion, NER

Biogas production, N-total, COD, pH

Antibiotic resistance genes (ARGs)

Aerobic vs anaerobic, sorption, pH, total solids, N, TOC, P

T, Eh, dry matter, O2, N-total, NH4-N, TOC, BOD

Transformation, NER

Manure-soil mixtures, transformation, NER

Manure-soil mixtures, transformation, NER, biocides

Sorption, liquid-solid distribution after cen-trifugation

Transformation

T, Eh, dry mass, pH, BOD, COD, total carbon, conductivity

TOC, conductivity, pH, P, NH4 Br-Na, K, Ca, Fe, Mg, Al, Si, Cu, Zn

14-N, Cl, NO3-

stoppers with inlet and outlet valves, 14CO2 trap

1.3-L laboratory model anaerobic three-neck glass reactor

100-mL glass amber wide mouth

<1300 mL

Amber glass vials with 20 mL teflon-lined caps, headspace filled with He

300-mL flasks, glass 50 g stoppers with inlet and outlet valves, 14CO2 trap

300-mL flasks, glass 50 g stoppers with inlet and outlet valves, 14CO2 trap

300-mL flasks, glass 50 g stoppers with inlet and outlet valves, 14CO2 trap

300-mL flasks, glass 50 g stoppers with inlet and outlet valves, 14CO2 trap

20-L stainless steel 15.5 L storage container with clipdown

Vacuum desiccator 1 L (Fig. 6)

300-mL flasks with 50 g 14CO2 trap

Amber 250-mL bot- <250 mL tles with teflon-lined caps served as reactors

7 days 3

15 days until 3 equilibrium of biogas production in

reactor

Sparged for 2 5 min with nitrogen

"Homogenized 3 stored in glass jars at 4 °C until use"

"The manure 3 was allowed to attain room temperature"

-20, 7, nd RT

112, 224

22 (-10) to 3

(-160)

5, 10, 20 (- 80) 30, 100, 177

20 (<120) 177

10, 20 (- 280) to 150 (- 329)

15, 25, nd 72

35, 45

Table 8 continued

Author (Year) Focus Setup Amount of manure Precondition- Repli- Study-r Eh (mV) Study

and param- ing/acclimati- cates (°C) duration

eters zation (days)

Loke et al. pH, Eh via indi- According to ISO 525.0 mL mineral <2 weeks stor- 4 21 nd 180

(2003) [45] cator, freely dissolved fraction 11734 [30], 1-L bottles; titanium(III) citrate as reducing agent medium, 50.0 mL manure, 100.0 mL stock solution age at 4 °C

Loke et al. Transforma- According to ISO 680 mL (water with 1 mm sieved, 4 20 nd 7

(2000) [44] tion, filtered vs non-filtered 11734 [30], volumes x 50, 680 mL 6.4 % manure) N2 bubbled through manure, stored at 4 and -20 °C before usage

Mitchell et al. pH, CH4, CO2 300-mL glass serum 200 mL nd 3 37 nd 40

(2013) [49] inhibition, total solids (TS) and VSS bottles fitted with rubber septum, headspace filled with N2, inoculum used

Mohring et al. Biogas produc- 5-L fermentors 1.89 kg manure, nd 2 37 nd 34

(2009) [50] tion, pH (Bigatec, Rheinberg, Germany), German VDI 4630 guideline, DIN 38414 part 8, control experiments in 500-mL flasks 1.89 L water, 0.42 kg inoculum

Riemensch- Biogas produc- 20-L laboratory-scale 15 kg nd 2 38 nd 44

neider et al. tion, batch reactor

(2014) [57] experiment and continuous feeding experiment

Schlusener Transformation Erlenmeyer flasks 100 g nd 1 20 nd 180

et al. (2006) closed with a

[59] fermenting tube

Shelver and pH, transfor- 2-L digester flasks nd nd 3 22, 38, nd 28

Varel (2012) mation 55

Shi et al. Methane pro- 1-L digester with gas 1 L (including 100 g nd 3 25 nd 20

(2011) [62] duction, pH, total solids absorbing bottle and collector bottle (Fig. 7) dry manure, 100 mL inoculum)

Stone et al. CH4, CO2, 120-mL batch reac- 50 g 105 days at 4 °C 3 10-20 nd 216

(2009) [64] volatile fatty acids, pH, Alkalinity, COD, VSS, VFA,hydrog- enotrophic metha- nogens, acetoclastic methano- gens tors, butyl rubber stoppers, head-space N2 purged (gradient)

Szatmari et al. Transformation 300-mL BOD bottles <300 mL nd nd 20 nd 112

(2011) [65] as used in closed bottle tests; referring to VICH [70]

Table 8 continued

Author (Year) Focus Setup Amount of manure Precondition- Repli- Study-7 Eh (mV) Study

and param- ing/acclimati- cates (°C) duration

eters zation (days)

Varel (2002) Odor, total 1-L Erlenmeyer flasks, 500 mL (feces, urine, nd 2 25 nd 62

[67] gas, VFA, N2-gas, rubber distilled water;

L-lactate, pH stopper 50:35:15)

Varel et al. Odor, pH, VFA, 2-L Erlenmeyer flasks 600 mL (1:1 seed slurry Establish- 2 22, 38, nd 25, 28

(2012) [68] aromatic with rubber stopper and fresh manure) ing "seed 55

fermentation slurry" over

products, 2-5 months

methane, for stabiliza-

coliforms tion of pH,

methane and

VFA produc-

Wang et al. Biogas 1.3-L laboratory <1300 mL Until equilibrium 3 20 nd 15

(2014) [72] production, model anaerobic of biogas

Shannon's three-neck glass production in

diversity reactor reactor

index (H'),

N-total, COD,

Wang et al. Transformation 3-L open beaker 1200 g 7 days at 23.2 °C 3 23.2 nd 40

(2015) [73] products,

total N,

abundance

of Bacillus

cereus

Widyasari- Non-extracta- 300-mL flasks, glass 75 g nd 2 20 (-189) to 170

Mehta et al. ble residues, stoppers with inlet (-21),

(2016) [76] redox poten- and outlet valves, (-274)

tial, pH CO2 trap

Winckler and T, transforma- 500-L tanks 295 L nd 4 8 - 48

Grafe (2001) tion

Zheng et al. T, transforma- 250-mL glass bottles <250 mL 1 day precondi- 3 35 (- 277) 52

(2012) [80] tion with teflon-lined tioning

screw caps, glove-

box, Na2S, N2

Zheng et al. T, transforma- 250-mL glass bottles <250 mL 1 day precondi- 3 15, 25, nd 65

(2013) [81] tion with teflon-lined tioning 35, 45

screw caps, glove-

box, Na2S, N2

nd not determined or not defined

the German VDI 4630 [69] guideline and to DIN 38414 part 8 [16], and Szatmari et al. [65] refer to the former draft of the EMA guideline on determining the fate of veterinary medicinal products in manure [19, 70].

Many of the studies try to establish anaerobic conditions using an inert gas for flushing headspace or solutions at the beginning of the experiments. Flow-through systems and batch systems (static or semi-static systems) are used. There is only one publication reporting a real flow-through system [2]. Ali et al. worked with a continuous flow-through of N2 and O2 in a defined ratio to establish a redox potential between -100 and +350 mV. With the addition of HCl or NaOH, the pH was adjusted.

Nearly all of the other studies report the usage of batch systems. They just use an inert gas at the beginning of the experiment (static) or periodically during the experiment (semi-static) to guarantee anoxic conditions for the sampling or to drive out the generated biogas. Nevertheless, it is often not well described how exactly produced biogas was driven out of the system or how it was dealt with the generated biogas overpressure. This is important for studies monitoring biogas production or for those studies working with 14C and monitoring mineralization, by trapping 14CO2 with a KOH solution for example [35]. Arikan et al. [6] used a water displacement technique to monitor biogas production. Mitchell et al. [49]

Zheng et al. 2012 Heuer et al. 2008 Joy et al. 2014 Angenent et al. 2008

Fig. 1 Citation map (generated via http://vwwv.mapequation.org, Edler and Rosvall [17]); each knot represents one publication, and each arrow visualizes the citation flow

worked with a syringe methodology to measure biogas production.

Others—not measuring biogas production—worked with closed glass bottles [11]. Kolz et al. [34] used amber glass vials with Teflon-lined caps. To achieve similar storage conditions as given during storage under a plastic cover in lagoons, Kuchta et al. [39] conducted their studies in 20-L stainless steel containers with clipdown covers. Schlusener et al. [59] used 300-mL Erlenmeyer flasks closed with fermenting tubes. Mohring et al. [50] worked with a commercially available anaerobic 5-L fermentor (Bigatec, Rheinberg, Germany). Winckler and Grafe [78] were one of the first to study the transformation of pharmaceuticals in liquid manure. They worked with very large 500-L tanks under outdoor and temperature-controlled conditions. In any case, these examples illustrate the aforementioned huge variety of different experimental approaches.

In contrast to the batch experiments, there are two publications working with an anaerobic sequencing batch reactor (ASBR). In the study of Angenent et al. [4], a 5-L ASBR was run by sequencing through a feed step, a react step, a settling step, and a decant step. An intermittent mixing process was thereby performed by biogas recycling. Tylosin half-life experiments were conducted by taking manure from the ASBR, placing it into capped 5-mL glass serum vials (pre-purged with N2), and spiking with tylosin. The vials were stored for a duration of 48 h at a temperature of 25 °C in a water bath. Cetecioglu et al. [14] also used an ASBR with a 24-h cycle to measure the impact of tetracycline on biogas production and the biodegradation of a synthetic organic substrate. In contrast to Angenent et al. [4], they monitored the tetracycline mass balance between the influent and the effluent of the ASBR considering the sludge inside the ASBR. With this setup, it was not possible to determine DT50 values. Huang et al. [29] and Wang et al. [72] also worked with a kind of ASBR. Riemenschneider et al. [57] worked with both a batch experiment and a constant feeding experiment using a 20-L laboratory-scale reactor. Grote et al. [21] only conducted the transformation study with a realistic outdoor scenario, working with chlortetracycline (CTC), sulfadiazine (SDZ), and trimethoprim (TMP). The medicated pigs excreted the pharmaceuticals over a long period of time, thus all relevant metabolites were considered. It is not easily possible to determine DT50 values for this approach, but it is possible to study the realistic transformation of a pharmaceutical.

Parameters

Summarizing, all the studies measured or controlled at least some of the following physical, chemical, and biological parameters during the transformation studies:

redox potential Eh (mV), dry matter content (%), pH, dissolved O2 content (mg/kg), NH4-N (g/kg), Ntotal (g/ kg), total organic carbon (TOC) (g/kg), total carbon (g/ kg), biological oxygen demand (BOD) (g/kg), chemical oxygen demand (COD) (g/kg), temperature (°C), volatile suspended solids (VSS), conductivity (|is/cm), P, Cl-, Br-, NO3-, Na, K, Ca, Fe, Mg, Al, Si, Cu, Zn, relative abundance of hydrogenotrophic methanogens and acetoclas-tic methanogens, volatile fatty acids (VFA) and aromatic fermentation products (L-lactate, acetate, propionate, isobutyrate, butyrate, isovalerate, valerate, isocaproate, caproate, phenol, ^-cresol, indole and skatole), methane/ biogas production, mineralization (%), 50 and 90 % disappearance time (DT50, DT90), transformation products (TP), non-extractable residues (NER), mass balance/ recovery (%), Shannon's diversity index (H'), log copy number/100 ng cDNA, liquid-solid distribution (/<d), and the number of antibiotic resistance genes (ARGs).

Aerobic vs. anaerobic conditions

The attempt of this literature review was to select studies that were conducted under primarily anaerobic conditions. The information is either stated by the author(s) or can be deduced from the given facts on the experimental setup. However, also studies are included that used aerobic conditions (e.g., redox potentials above -100 mV, [52]). Various authors merely assume anaerobic conditions without any further indication. Besides, different authors use different terminologies, such as "anaerobic digestion," "anaerobic conditions," "methanogenic conditions," and "anaerobic tightly capped vessels." Studies with this vague information were still considered in this examination as otherwise the relevant publications would have been limited to a number of only seven studies reporting a redox potential.

Besides using closed laboratory setups, many studies report the use of N2 or He gas to purge the headspaces of the systems or to purge the used liquids and manures before starting the experiments. Others used the glove-box technique [80] or added reducing agents to the manures to guarantee reducing conditions (e.g., Na2S by Alvarez et al. [3] or titanium(III)citrate by Loke et al. [45]). Loke et al. [45] further added resazurin as a redox indicator. As the test bottles did not show a reddish coloring, they assumed anaerobic conditions. However, it might be difficult to interpret the coloring of this also pH-dependent indicator in deep brown liquid manure. For this, they also monitored methane gas production as a main indicator for methanogenic and, by this, anaerobic conditions. Varel et al. [68] systematically studied methane production of their seed manure before starting transformation studies with this manure in order to be able to work with stable methanogenic/anaerobic conditions.

Kuhne et al. [40] used closed incubation systems to investigate the stability of tetracycline in pig manure. They determined that the DT50 for tetracycline in their unventilated systems was 9 days, whereas it was 4.5 days when the slurry was ventilated.

Szatmari et al. [65] compared an anaerobic laboratory study with a field study using manure composting. In the laboratory experiment, more than 30 % and in the field study about 10 % of the initial doxycycline amount could be detected in manure samples after 12 and 16 weeks of aging, respectively. The half-life of doxycycline in manure was calculated to be 52.5 days under anaerobic conditions and 25.7 days under aerobic conditions.

Ali et al. [2] were the only of all included studies who deliberately varied the redox potential. They established a set of microcosms with controlled redox potentials (Eh) (-100 mV, 0 mV, +250 mV, and +350 mV) and pH conditions (pH 5.5, 7.0, and 8.5). With increasing Eh—that is with increasing aerobic conditions—they found significantly higher dissipation rates for tylosin and could attribute this to microbial activity by comparison with sodium azide-treated samples. Increasing pH resulted in increasing dissipation rates. With the addition of azide, a decrease of Eh could be observed. Kolz et al. [34] worked with redox potentials of slurry between -10 and -80 mV. The addition of azide resulted in a decrease of the redox potential to between -90 and -160 mV.

Although redox potential is not directly a proof of anaerobic conditions, it is relatively easy to measure in liquid manure. The internationally harmonized OECD guideline 308 on the transformation of chemicals in water/sediment systems pragmatically sets a maximum upper limit of -100 mV [52] for anaerobic conditions. Strictly considering this limit of -100 mV, only 3-4 studies meet the requirements for anaerobic conditions (Ali et al. [2], Lamshoft et al. [41], Widyasari-Mehta et al. [76], Zheng et al. [81]). It should be considered that redox potentials measured in real manure tanks are even far below -100 mV [74]. Generally, the transformation of VMPs in manure is faster and more complete under aerobic conditions than under anaerobic conditions.

Methane production and microbial activity

The production of methane was considered as an ongoing parameter in 12 studies. In two studies with tetracyclines, Arikan et al. [6] and Alvarez et al. [3] found that methane production was reduced by 27 % during batch experiments and up to 62 % due to antibiotic dosage, respectively. Stone et al. [64] found that the generation of methane was inhibited by 27.8 % due to the presence of chlortetracycline. Dependent on the dosage, Cetecioglu et al. [14] determined adverse impact of tetracycline with a total collapse of the microbial activity and metabolic

functions at a concentration of 8.5 mg/L in a synthetic substrate mixture under anaerobic conditions. Shi et al. [62] found a dosage-dependent inhibition on CH4 production and concluded that antibiotics appear to inhibit bacterial activity, resulting in a delay and overall decline in CH4 production. Among these 12 studies measuring biogas production, four studies were explicitly concerned with microbiological issues [1, 26, 64, 72]. Varel et al. [68] mention that an adaption period of 5-6 months was necessary for acclimatization of microorganisms to monen-sin and to reduce effects of antimicrobials on methane production. Others added small amounts of an inoculum from an anaerobic digester at a farm, or from a waste-water treatment plant, or a biogas plant [3, 5, 49, 50, 62]. Besides the topic of transformation in manure, Ma et al. [47] for example isolated a novel strain of bacteria capable of degrading 100 % tylosin within 72 h. Against that background, each future transformation study has to be analyzed critically. Composition of microbial community has a massive effect on transformation rates and routes. Without any further qualitative and quantitative critical analysis of microbiology, it is not possible to produce reliable and reproducible transformation data of VMPs and biocides in liquid manure. From a regulatory point of view, this topic could enable a massive manipulation of transformation data. Therefore, using a reference substance for transformation studies seems necessary.

Biotic vs. abiotic transformation

In some studies, either sterilization with sodium azide or autoclaving allowed to differentiate between abiotic and biotic transformation. Generally, biotic transformation rates can be substantially higher than pure abiotic transformation rates. However, the process of formation of non-extractable residues cannot be elucidated by this approach.

Loke et al. [45] worked with autoclaved and non-auto-claved manure to study the transformation of oxytetracy-cline (OTC) by measuring the free concentration of the VMP. By this, they did not find a difference between the sterile and the non-sterile setups, due to the fast sorption of OTC to the solid phase. They did not address the question of whether the following biotic transformation is inhibited by sorption of the substance to suspended solids.

Loke et al. [44] studied the transformation of tylosin A but were unfortunately not able to figure out whether the rapid decrease in the concentration of tylosin A is caused by sorption or abiotic or biotic chemical degradation. Ali et al. [2] later reported, among other conclusions, that microbial degradation was much greater under aerobic (Eh +350 mV) conditions than under anaerobic conditions as compared to abiotic transformation or

sorption. Kolz et al. [34] concluded that both biodegradation and abiotic degradation occur during the transformation of tylosin. However, strong sorption to slurry solids was probably the primary mechanism of tylosin disappearance.

Zheng et al. [80] found that the transformation of 17a-estradiol, 17p-estradiol, and estrone was mainly dominated by biodegradation rather than by physical or chemical transformation.

Li et al. [42] found that the combined processes of hydrolysis and biodegradation were responsible for the transformation of ceftiofur. The determined hydrolysis and total degradation rate constants in aqueous solutions varied according to temperature.

Study temperature

Study temperatures within the considered publications ranged from 5 to 55 °C. Only few publications explicitly analyzed the effects caused by a variation of the study temperature.

Harms [25] examined the stability of pharmaceuticals in manure during storage at 7 °C and found no degradation of chlortetracycline during 6 months. Sulfadiazine was reduced to 50 % after 1 week, but the remaining residuals were stable until the end of the trial (32 weeks). The author varied the storage temperature (-20, 7 °C, room temperature) over a period of 16 weeks. Sulfamera-zine, sulfamethoxypyrazine, sulfaguanidine, and sulfiso-medine persisted. Sulfamethoxazole was reduced up to 80 % at 7 °C as well as at room temperature. The same degradation rate was reached more quickly with higher temperatures than with cooler conditions of storage. Enrofloxacin and tiamulin were reduced to 20 % at 7 °C storage temperature. For tiamulin, a reduction of 10 % at 7 °C and 25 % at room temperature was observed. Only sulfapyridazine and enrofloxacin showed a small decline at a storage temperature of -20 °C.

Li et al. [42] studied the transformation of ceftiofur at temperatures between 15 and 45 °C and found increasing hydrolysis and biodegradation rates with temperature. Increasing the study temperature from 35 to 45 °C resulted in an increasing relevance of hydrolysis on transformation of ceftiofur, whereas biodegradation remained static.

Similarly, Varel et al. [68] found principally increasing dissipation rates with increasing the temperature from 22 to 55 °C. They studied the effect of anaerobic digestion at different temperatures, among other parameters, on the fate of chlortetracycline (CTC) in pig manure and monensin (MON) in cattle manure. The authors concluded that anaerobic digestion at elevated temperatures may be an effective treatment to reduce CTC but not MON. Transformation of CTC mainly depends on abiotic transformation. This was also shown by Shelver and

Varel [61] who also worked with CTC between 22 and

55 °C.

Stone et al. [64] worked with a temperature gradient to simulate field conditions commonly found in the northern mid-western United States of America. They started with 10 °C (0-30 days) and increased the temperature over time: 12 °C (30-46 days), 15 °C (46-56 days), and 20 °C (56-216 days).

Half of the studies (21 out of 42) were conducted at ambient temperatures (ranging from 20 to 25 °C). Some other experiments were performed at elevated temperatures of 35 to 40 °C, which enhances the microbial activity [5, 32, 57]. In general, transformation was found to be dependent on the study temperature; increasing temperatures simultaneously result in increasing transformation rates. Working with temperatures above the microbiological relevant limit of 35-40 °C results in an inhibition of microbial activity and biodegradation processes. In which way this affects transformation processes mainly depends on the transformation routes of different substances.

Conclusions

The available studies on the transformation of biocides and veterinary medicinal products in manure show large variations in the experimental setup and conditions such as temperature, redox potential, matrix effects, and physico-chemical properties.

Most frequently investigated VMPs belong to the class of antibiotics, namely sulfonamides, tetracyclines, and macrolide antibiotics. In 16 out of the 42 studies, excrements or manure from a medicated livestock was considered; all other studies are based on spiked manure. There were only three publications working with biocides, which clearly shows that this topic is largely neglected by research. Most of the studies considered manure originating from pigs (28 out of 42), while the remaining studies investigated manure from cattle or in one case synthetic manure was used. Study duration and temperature ranged from 2 to 374 days and 5 to 55 °C, respectively. Many studies do not report the basic parameters. Only seven publications give information on the redox potential of the manure used for transformation. Further, the characterization of the matrix in many cases is inadequate due to missing basic parameters such as dry matter content and pH. Information on dissipation rates or half-lives, transformation products, formation of methane, microbiology, and non-extractable residues (NER) are not available in the majority of the considered publications.

Overall, it can be stated that the majority of the studies describe at least one fundamental parameter of the experimental conditions poorly. Considering all the different approaches, one can conclude that it is inevitable

to give specific guidance for studies on the transformation in manure in general and especially with regard to the applicability and acceptability of studies in regulatory contexts. All the parameters—as they are studied particularly within single publications—affect the basic outcome of a transformation study. It is therefore necessary to standardize them or at least measure and report them individually. Parameters such as temperature, dry matter content, origin and preconditioning of the manure, microbiology, pH, and redox potential do have massive effects on the transformation rates or routes of VMPs and biocides in liquid manure. Some of these parameters are relatively simple to measure and should be monitored mandatorily, or even standardized where possible. Only one transformation study at real manure storage tanks was found. This is an important area for research to study transformation processes under realistic conditions. Comparing such authentic outdoor results with those produced on laboratory scale is important to validate the outcome of laboratory studies and to evaluate different experimental setups. One of the most challenging topics with knowledge gaps is related to the composition, the development or spread of resistance, or the adaption and activity of the microbial community. For future studies, this topic should always be addressed.

As an outcome of the summarized monitoring studies, it can be concluded that VMPs occur ubiquitously in manure. Biocides are totally neglected until today. For sulfadiazine and chlortetracycline, concentrations exceeding predicted environmental concentrations were found. For future monitoring studies, it should be obligatory in terms of environmental risk assessment to define the exact animal type as the origin of the manure and to measure and report nitrogen content and dry matter content of the analyzed manures. From our point of view, it would be helpful to imply a Europe-wide monitoring program to evaluate the calculated PECs of VMPs in liquid manure.

Abbreviations

ASBR: anaerobic sequencing batch reactor; BOD: biological oxygen demand; CAFO: concentrated animal feeding operation; COD: chemical oxygen demand; CTC: chlortetracycline; CYN: cyanamide; DAD: diode array detector; DIF: difloxacin; DIN: German Institute for Standardization (german: Deutsches Institut für Normung e.V.); DT50: time needed for disappearance of 50 % of the parent compound, disappearance time; DT90: time needed for disappearance of 90 % of the parent compound, disappearance time; dw: dry weight; ELISA: enzyme-linked immunosorbent assay; EMA: European Medicines Agency; ERA: environmental risk assessment; ERY: erythromycin; EU: European Union; F + E: research and development (German: Forschung und Entwicklung); FEN: fen-bendazole; FKZ: project no. (German: Forschungskennzahl); FLU: flubendazole; GC: gas chromatography; HPLC: high-performance liquid chromatography; HR-MS: high-resolution mass spectrometry; IMZ: imazalil; ISO: International Organization for Standardization; LC: liquid chromatography; LIN: lincomycin; LOD: limit of detection; LSC: liquid scintillation counting; MEC: measured environmental concentration; MON: monensin; MS: mass spectrometry; nd: not determined or not defined; NER: non-extractable residues; ns: not

specified; OECD: Organisation for Economic co-operation and Development; OTC: oxytetracycline; PEC: predicted environmental concentration; RTLC: radio thin-layer chromatography; SCP: sulfachloropyridazine; SDZ: sulfadiazine; SMZ: sulfamethoxazole; SPN: spectinomycin; TMP: trimethoprim; TOC: total organic carbon; TP: transformation product; TS: total solids; TYL: tylosin; UV: ultraviolet; VDI: Association of German Engineers (German: Verein Deutscher Ingenieure); VFA: volatile fatty acid; VICH: Veterinary International Conference on Harmonization; VMP: veterinary medicinal product; VSS: volatile suspended solids; ww: wet weight.

Authors' contributions

MW, SB, TJ, SK, and RAD were substantially involved in the conception and design of the study. SB and SK gave the background information on regulatory affairs. MW and LS were responsible for the acquisition and analysis of the data. MW drafted the manuscript. All authors read and approved the final manuscript.

Author details

1 Institute of Soil Science and Soil Conservation, IFZ, Justus Liebig University Giessen, Heinrich-Buff-Ring 26-32, 35392 Giessen, Germany. 2 Unit IV 2.2 Pharmaceuticals, Washing and Cleansing Agents and Nanomaterials, German Environment Agency (UBA), Dessau-Roßlau, Germany. 3 ECT Oekotoxikologie GmbH, Flörsheim, Germany.

Acknowledgements

The present study was funded by the German Federal Ministry for the Environment, Nature Conservation, Building and Nuclear Safety (Grant No. 3712 65 420).

Competing interests

The authors declare that they have no competing interests.

Received: 6 May 2016 Accepted: 12 September 2016 Published online: 26 September 2016

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