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Published online 1 May 2008
Published in J Environ Qual 37:1245-1253 (2008)
DOI: 10.2134/jeq2007.0399
© 2008 American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America
677 S. Segoe Rd., Madison, WI 53711 USA
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TECHNICAL REPORTS

Organic Compounds in the Environment

Antibiotic Degradation during Manure Composting

Holly Dollivera, Satish Guptab,* and Sally Nollc

a Department of Plant and Earth Science, Univ. of Wisconsin-River Falls, 410 S. 3rd St., River Falls, WI, 54022
b Dep. of Soil, Water, and Climate, Univ. of Minnesota, 1991 Upper Buford Circle, St. Paul, MN 55108
c Dep. of Animal Science, Univ. of Minnesota, 1364 Eckles Ave., St. Paul, MN 55108

* Corresponding author (sgupta{at}umn.edu).

Received for publication July 26, 2007.

   ABSTRACT
TOP
 NOTES
 ABSTRACT
INTRODUCTION
 Materials and Methods
 Results
 Discussion
 Conclusions
 REFERENCES
 
On-farm manure management practices, such as composting, may provide a practical and economical option for reducing antibiotic concentrations in manure before land application, thereby minimizing the potential for environmental contamination. The objective of this study was to quantify degradation of chlortetracycline, monensin, sulfamethazine, and tylosin in spiked turkey (Meleagris gallopavo) litter during composting. Three manure composting treatments were evaluated: a control treatment (manure pile with no disturbance or adjustments after initial mixing), a managed compost pile (weekly mixing and moisture content adjustments), and vessel composting. Despite significant differences in temperature, mass, and nutrient losses between the composting treatments and the control, there was no difference in antibiotic degradation among the treatments. Chlortetracycline concentrations declined rapidly during composting, whereas monensin and tylosin concentrations declined gradually in all three treatments. There was no degradation of sulfamethazine in any of treatments. At the conclusion of the composting period (22–35 d), there was >99% reduction in chlortetracycline, whereas monensin and tylosin reduction ranged from 54 to 76% in all three treatments. Assuming first-order decay, the half-lives for chlortetracycline, monensin, and tylosin were 1, 17, and 19 d, respectively. These data suggest that managed compositing in a manure pile or in a vessel is not better than the control treatment in degrading certain antibiotics in manure. Therefore, low-level manure management, such as stockpiling, after an initial adjustment of water content may be a practical and economical option for livestock producers in reducing antibiotic levels in manure before land application.

Abbreviations: ELISA, enzyme-linked immunosorbent assay


   INTRODUCTION
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
Materials and Methods
 Results
 Discussion
 Conclusions
 REFERENCES
 
IT is estimated that between 9 and 13 million kg of antibiotics are used annually in the USA for agricultural purposes (Shea, 2003). The majority of agricultural antibiotic usage is for subtherapeutic purposes (i.e., prophylaxis and growth promotion). Most antibiotics are partially metabolized by animals, and portions often exceeding 70% of administered dosage are excreted as parent compounds or metabolites in manure (Kumar et al., 2005). A review by Kumar et al. (2005) found that antibiotic concentrations in manure ranged from trace levels to >200 mg kg–1 or L–1, with typical concentrations in the 1 to 10 mg kg–1 or L–1 range.

The vast majority of manure is applied to agricultural land as a nutrient source for crops. Annually, approximately 9 million ha of land receive manure applications in the USA (USDA-NASS, 2005). There is growing concern that land-applied antibiotics in manure are reaching surface and ground waters (Kay et al., 2004; Kay et al., 2005; Burkhardt et al., 2005; Kreuzig et al., 2005; Davis et al., 2006) and ultimately contributing to the development and spread of antibiotic resistance in the environment (Phillips et al., 2004; Khachatourians, 1998; Pruden et al., 2006). On-farm manure management strategies, such as composting, may provide a practical and economical option to reduce antibiotic concentrations in manure before land application and thereby decrease environmental risks.

Composting is a controlled aerobic process by which diverse groups of microorganisms decompose organic materials, producing stable organic and inorganic byproducts (Rynk, 1992). During the composting process, temperatures often exceed 40°C as a result of intense biological activity. Composting of animal manure has been done primarily for odor management (Rynk, 1992) and to prevent contamination of crops from pathogens (Larney et al., 2003). Composting can also reduce the cost of manure transportation. However, composting has also been shown to be an effective bioremediation strategy for soil, biosolids, and/or manure contaminated with explosives (e.g., Williams et al., 1992), aromatic and petroleum hydrocarbons (Semple et al., 2001), pesticides (Büyüksönmez et al., 2000), personal care products (Xia et al., 2005), and hormones (Hakk et al., 2005). For example, Hakk et al. (2005) showed that water-soluble 17β-estradiol and testosterone decreased by more than 80% after 139 d of composting poultry manure.

There is limited information on antibiotic degradation during manure composting. A study by van Dijk and Keukens (2000) showed that sulfachlorpyrazine concentrations in poultry manure decreased by 58 to 82% during 8 d of composting. Storage of the same manure for 3 mo after composting resulted in an additional 33% reduction in antibiotic concentrations. A laboratory experiment by Arikan et al. (2007) found >99% removal of oxytetracycline during 35 d of beef (Bos taurus) manure composting, whereas only minimal reduction (<15%) was observed for manure incubated at room temperature.

The objective of this study was to quantify degradation of chlortetracycline, monensin, sulfamethazine, and tylosin in spiked turkey litter during composting. These compounds were selected due to their prevalent use in animal agriculture (Kumar et al., 2005). Turkey litter was used as a model for the study of antibiotic degradation during composting.


   Materials and Methods
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 Materials and Methods
Results
 Discussion
 Conclusions
 REFERENCES
 
Manure and Composting Facility
The composting study was conducted at the University of Minnesota Turkey Research Center at Rosemount, Minnesota. The 328-m2 facility consisted of a poured concrete floor with welded wire walls above a 1-m high solid bottom. A combination of fans and curtains facilitated ventilation. Manure was generated from approximately 800 tom turkeys, which were housed in the facility before composting. Turkeys were fed a commercial diet, which was supplemented with bacitracin (55.1 g Mg–1 of feed). During Week 9 of the production cycle, water was supplemented with chlortetracycline for a 5-d period; however, residual chlortetracycline was not detected in manure at the start of the composting experiment. Bedding material was a 50:50 blend of aspen (Populus tremuloides Michx.) shavings and sunflower (Helianthus annuus) hulls. The carbon to nitrogen ratio of the manure (including bedding) was 13.3. Manure was periodically mixed and amended with Poultry Guard (Oil Dri Corporation of America, Chicago, IL) to control ammonia volatilization. Turkeys were marketed at 18 wk, at an average weight of 15 kg.

The composting study began shortly after the turkeys were marketed. Composting was done indoors to eliminate antibiotic losses in runoff from precipitation events. Although composting was done in late fall and early winter, the facility was not heated. With the exception of sulfamethazine, manure was spiked with dry mix feed-grade antibiotics. Chlortetracycline (53 g) was applied as Pennchlor (Pennfield Oil Company, Omaha NE), monensin (53 g) as Rumensin (Elanco Animal Health, Greenfield, IN), and tylosin (52 g) as Tylan (Elanco Animal Health). Due to the unavailability of sulfamethazine as a single feed-grade supplement, sulfamethazine (24 g) was applied as a pure compound (Sigma Aldrich, St. Louis, MO).

Table 1 lists the physiochemical characteristics of antibiotics evaluated in this study. With the exception of monensin, these antibiotics are soluble in water. Chlortetracycline and tylosin are strongly sorbed to solids as indicated by high Kd values, which limits their mobility in the environment. Monensin and sulfamethazine are less attracted (low Kd values) to solids. All of the antibiotics and the antibiotic-containing feeds were mixed together and hand broadcasted over the manure. Manure was mixed for 1.5 h with a front-end bucket loader to uniformly incorporate the antibiotics into the manure. At the same time antibiotics were mixed with manure, water was added to bring the moisture content of the manure to approximately 0.4 g g–1, which is the optimal water content for composting (Rynk, 1992).


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  		Table 1. Physiochemical characteristics of the antibiotics evaluated in this study.

 
Composting Treatments
Control
After antibiotic addition and water mixing, approximately 12 m3 of turkey manure was piled with a front-end bucket loader into an elongated pile to simulate a small windrow. The manure pile was approximately 4.6 m long, 3.7 m wide at the base, and 1.6 m high in the center. After the manure was piled, there was no adjustment of the moisture content or aeration (i.e., mixing) during the 35-d study period. This treatment simulates unmanaged composting and is somewhat similar to manure stockpiling, a common practice on farms due to time and practical constraints associated with land application of manure.

Managed Composting
For the managed composting treatment, manure was piled similar to the control pile (i.e., 12 m3; 4.6 m x 3.7 m x 1.6 m). In contrast to the control pile, manure in the managed composting pile was adjusted weekly with water additions and mixing (i.e., aeration) to maintain optimal composting conditions. During weekly management, the manure pile was flattened with a front-end bucket loader, followed by spraying and mixing of approximately 95 L of water over a 20-min period and re-piling of the manure. Water addition and compost mixing was done on Day 7, 16, 22, and 29. As with the control treatment, composting was done for 35 d for managed composting treatment.

Vessel Composting
The vessel composting unit was a horizontal steel insulated rotating drum, 2.4 m long and 1.2 m in diameter (Fig. 1 ) (I.D.X. Environmental, Inc., Brainerd, MN). The volume of manure composted in the vessel unit was approximately 2 m3. After the manure was loaded, the unit rotated continuously at 0.3 revolutions min–1. Natural aeration was provided through small vents on the vessel. After loading of the vessel, no additional management (i.e., moisture content adjustment) was applied. Manure was composted inside the vessel for 8 d, which is representative of typical vessel operations (Rynk, 1992). After the initial vessel composting phase, the vessel was unloaded, and manure was allowed to cure for an additional 14 d.


Figure 1
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  		Fig. 1. Schematic and picture of the vessel composting unit.

 
The temperature was monitored twice daily for all three treatments using a 90-cm-long Atkins Temptec VersaTuff Probe (Atkins Technical Inc., Gainesville, FL). Due to variability, temperature measurements were made at multiple locations within the manure piles and the vessel unit (i.e., top, middle, and bottom) and averaged.

Compost Sampling
The control and the managed compost pile treatments were sampled on Day 0, 7, 16, 22, 29, and 35. For the managed compost pile, manure was sampled before moisture content adjustments and mixing. Manure from the vessel unit was sampled on Day 0, 2, 4, 6, 8, 16, and 22. In all samplings, three composite samples were taken from each treatment. Each composite sample was made up of three subsamples taken 30 cm below the surface of the manure from the top, middle, and bottom of the pile. For the vessel treatment, each composite sample was made up of samples taken from the front, middle, and back of the vessel. After collection, samples were immediately frozen at –20°C. Along with antibiotic analysis, manure samples were analyzed for moisture content and ash content (550°C, 2 h). Initial and final manure samples from each treatment were analyzed for changes in total carbon by high-temperature combustion (Elementar Vario EL; Elementar Analysensysteme GmbH, Hanau, Germany), total (Kjeldahl) nitrogen by wet digestion, and pH (1:10 suspension) (Peters, 2003)

Antibiotic Analysis
Manure samples were prepared for antibiotic analysis by thawing at room temperature followed by manual mixing/homogenization. Water-extractable and total-extractable antibiotics were measured. For water-extractable antibiotics, 5 g of manure was mixed with 10 mL of nano-pure water, vortexed for 1 min, shaken on an end-over-end shaker for 15 min at 4°C, and centrifuged at 2000 g for 20 min, and the supernatant was collected. The same extraction was repeated with an additional 10 mL of nano-pure water. Supernatants were combined, centrifuged at 2000 g for 20 min, and filtered through a nonsorptive 0.45-µm filter. For total-extractable antibiotics, the remaining solids were mixed with 10 mL of an 80:20 (v/v) methanol:water solution, vortexed, shaken, and centrifuged, and the supernatant was collected. The same extraction was repeated with an additional 5 mL of the methanol:water solution. The supernatants were combined, centrifuged, and filtered as described for the water extraction. Antibiotic degradation in this study is measured as a decrease in total-extractable antibiotic concentrations over time. This extraction process is similar to the process described by Hakk et al. (2005), which achieved approximately 100% recovery of 17β-estradiol and testosterone from spiked poultry manure. Recovery of antibiotics from manure was not quantified in this study and was assumed to remain constant over time.

Antibiotic analysis was conducted using enzyme-linked immunosorbent assay (ELISA) analysis. The basis of ELISA analysis is a highly specific and sensitive antibody–antigen reaction. Commercially available tetracycline (r-Biopharm, South Marshall, MI), monensin (Immuno-Diagnostic Reagents, Vista, CA), sulfamethazine (Neogen Corporation, Lexington, KY), and tylosin (International Diagnostic Systems Corporation, St. Joseph, MI) ELISA kits for residue analysis in food products were adapted for analysis of manure samples (Kumar et al., 2004; Dolliver, 2007; Dolliver et al., 2008). Analysis was preformed as instructed by the kit manufacturer. Quantification was performed at the specified wavelength using a spectrophotometer (Molecular Devices, Sunnyvale, CA). The tetracycline kit had 100% cross-reactivity toward chlortetracycline (Kumar et al., 2004). There was no cross-reactivity for the antibiotics used in this study between kits. Limits of quantification were 0.25 µg L–1 for chlortetracycline and tylosin, 2.0 µg L–1 for sulfamethazine, and 3.0 µg L–1 for monensin. These limits of quantification correspond to water-soluble concentration of 1 µg kg–1 of manure for chlortetracycline and tylosin, 8 µg kg–1 of manure for sulfamethazine, and 12 µg kg–1 of manure for monensin. Standard curves (r2 > 0.95) were constructed for each kit with standards run in triplicate.

Greater than a 1:20 dilution with kit-specific dilution buffer was performed to offset the matrix interferences associated with the turkey manure (Dolliver et al., 2008). Composite manure samples were run in singlicate, with approximately 10% of samples randomly selected for duplicate analysis. The coefficient of variation for intra- and interplate variability was <20%.

Statistical Analysis
Statistical analyses were performed using the PROC GLM procedure in SAS 9.1 (SAS Institute Inc., 2004). Differences between the treatments were evaluated using the LSMEANS statement. Effects were considered significant at P ≤ 0.10. Because of the loss of mass during composting, antibiotic and nutrient concentrations (mg kg–1 of manure) at any sampling time were adjusted back to initial dry weight (Table 2 ). The adjustment was done using the following relationship:

Formula 1[1]
where CiADJ is the mass loss adjusted antibiotic or nutrient concentration (mg kg–1 of initial dry weight) at sampling time i, Ci is the measured antibiotic or nutrient concentration at time i, Ash0 is the ash content at time zero (mg kg–1 of initial dry weight), and Ashi is the ash content at time i (mg kg–1 of dry weight of the manure at time i).


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  		Table 2. Properties of the turkey manure before and after stockpiling and composting (mean ± SD). With the exception of moisture content, data are presented on a dry weight basis with correction for mass loss.

 

   Results
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 Materials and Methods
 Results
Discussion
 Conclusions
 REFERENCES
 
Composting Process
Thermophilic temperatures (>40°C) were reached in all three treatments within 4 d (Fig. 2 ). For the control treatment, manure temperature peaked between Days 6 through 14 and declined thereafter (Fig. 2). For the managed composting treatment, manure temperature declined approximately 25% immediately after watering and mixing and increased to approximately 60°C during the interval between mixings (Fig. 2). For the vessel treatment, the temperature of the manure was consistently above 60°C throughout the duration of the active composting phase (Fig. 2). Temperature was not recorded during the curing phase of the vessel treatment. Peak manure temperatures for the control, managed composting, and vessel composting treatments were 54, 61, and 64°C, respectively.


Figure 2
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  		Fig. 2. Average temperature of turkey manure during composting by treatment. Asterisks indicate days when the high-management compost pile was watered and mixed. Dashed line indicates the mesophilic-thermophilic temperature boundary.

 
Ash content of the manure increased for all three treatments (Table 2). Statistically, ash content of the manure was higher for the managed and the vessel composting treatments compared with the initial ash content of the manure. There was no statistical difference in ash content between the manure from the managed composting and the vessel composting treatments. Because there were no sources of mineral additions in this study (i.e., protected indoor environment and concrete flooring), the increase in ash content is a result of mass loss due to organic matter decomposition. The increase in ash content corresponded to mass losses of 12.5, 20.7, and 28.5% for the control, managed composting, and vessel composting treatments, respectively. Due to the short duration of this study, mass losses were lower than the normal range of 35 to 50% reported in the literature (Rynk, 1992).

Total carbon and nitrogen significantly decreased in all three composting treatments (Table 2). Carbon losses ranged from 15% for the control treatment to an average of 25% for the managed composting and vessel composting treatments. Similarly, ammonia losses were 18% for the control treatment and averaged 28% for the managed and vessel composting treatments. Statistically, carbon and nitrogen losses were lower in the control treatment compared with the managed and vessel treatments; however, there was no difference between the managed and vessel composting treatments. The low initial C:N ratio (<14:1) and high pH (>8.0) likely resulted in nitrogen volatilization, contributing to high nitrogen losses in all three treatments (Martins and Dewes, 1992). There was little change in the C:N ratio in all three treatments (Table 2), which is attributed to these high nitrogen losses. Considering the short duration (8–35 d) of this study, carbon and nitrogen losses in this study are similar to values reported in the literature (Eghball et al., 1997; Tiquia et al., 2002).

Collectively, temperature, mass, and nutrient data suggest that composting intensity was relatively similar for the managed and the vessel composting treatments (Table 2). However, composting intensity was lower in the control treatment, as indicated by lower temperature and lower mass and nutrient losses (Table 2). This was expected because optimal conditions (aeration and moisture content) for microbial activity were not maintained in the control treatment.

Antibiotic Degradation
Initial total-extractable concentrations of antibiotics after mixing were approximately 1.5 mg kg–1 for chlortetracycline (Fig. 3 ), 11.9 mg kg–1 for monensin (Fig. 4 ), 3.7 mg kg–1 for tylosin (Fig. 5 ), and 10.8 mg kg–1for sulfamethazine (Fig. 6 ). These concentrations are within the range of antibiotic concentrations found in animal manure (Kumar et al., 2005). Concentrations of monensin and tylosin increased after the start of the study (Fig. 4 and 5). Differences in initial concentrations and first sampling may represent a combination of factors, such as slow solubility of feed-based antibiotics and spatial variability. For monensin, sulfamethazine, and tylosin, initial concentrations (Day 0) are presented as open circles in Fig. 4, 5, and 6 but were excluded from best fit decay functions.


Figure 3
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  		Fig. 3. Total extractable chlortetracycline concentration with time during (A) low management, (B) high management, and (C) vessel composting. Data are fitted with a first-order decay function.

 

Figure 4
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  		Fig. 4. Total extractable monensin concentration with time during (A) low management, (B) high management, and (C) vessel composting. Data are fitted with a first-order decay function. Open circles indicate concentrations on Day 0, which are not included in the decay function. Error bars represent SD of the mean.

 

Figure 5
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  		Fig. 5. Total extractable tylosin concentration with time during (A) low management, (B) high management, and (C) vessel composting. Data are fitted with a first-order decay function. Open circles indicate concentrations on Day 0, which are not included in the decay function. Error bars represent SD of the mean.

 

Figure 6
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  		Fig. 6. Total extractable sulfamethazine concentration with time during (A) low management, (B) high management, and (C) vessel composting. Data are fitted with a first-order decay function. Open circles indicate concentrations on Day 0, which are not included in the decay function. Error bars represent SD of the mean.

 
Total-extractable chlortetracycline declined rapidly in all three treatments, with >99% reduction occurring in less than 10 d (Fig. 3). However, chlortetracycline concentrations near the limit of quantification were measured on the final day of the study period in all three treatments. Total-extractable monensin and tylosin exhibited a gradual decline over time, with reductions ranging from 54 to 76% (Fig. 4 and 5). There was no change in total-extractable sulfamethazine concentrations in any of the treatments (Fig. 6). With the exception of chlortetracycline, coefficients of variability between samples in a given day and treatment commonly exceeded 15% (Fig. 3–6GoGoGo). The coefficient of variation for chlortetracycline was <10%.

Except for sulfamethazine, which did not degrade, antibiotic degradation seemed to follow the first-order decay function:

Formula 2[2]
where C is the measured antibiotic concentration (mg kg–1) at time (t) (day), Co is the initial antibiotic concentration (mg kg–1), and k is the antibiotic degradation rate constant (d–1). Using this decay model, half-life was calculated as:

Formula 3[3]
The average r2 value for model fit was >0.9 for chlortetracycline and approximately 0.6 for monensin and tylosin. Rate constants and calculated half-lives are presented in Table 3 . Rate constants for chlortetracycline varied from approximately 0.67 to 0.87 d–1, with a half-life varying from 0.8 to 1 d. Monensin and tylosin degradation were similar, with decay rates varying from 0.03 to 0.06 d–1. The average half-lives of monensin and tylosin were approximately 17 and 19 d, respectively (Table 3). In general, decay rates were slightly lower and half-lives were slightly higher for the control treatment compared with the high-management and the vessel composting treatments (Table 3). However, there was no statistical difference in total-extractable antibiotic concentrations among the three treatments on the final day of the study period.


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  		Table 3. First-order degradation rate constant (–k) and half-life (t1/2) of chlortetracycline, monensin, sulfamethazine, and tylosin by treatments.

 
Water-extractable antibiotics may represent the most "available" form for degradation by microorganisms. Initial water-extractable antibiotic concentration varied from approximately 40% of total-extractable for monensin to 100% for chlortetracycline (Table 4 ). Initial water-extractable concentrations for sulfamethazine and tylosin were approximately 85% of the total-extractable concentration.


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  		Table 4. Percentage of water-extractable antibiotics (mean ± SD) before and after stockpiling (control) and composting. Data are averaged over three treatments (control, managed composting, and vessel composting).

 
Relative to the control, there was no effect of treatment on water extractability for any of the antibiotics studied (data not shown). The water extractability data in Table 4 are therefore averaged over all three treatments. Between the initial and final sampling, there was no change in water-extractable chlortetracycline (Table 4). However, water-extractable monensin, sulfamethazine, and tylosin were statistically lower on the final day compared with the initial day of the study (Table 4). The reduction in the proportion of antibiotics that were water extractable during storage and composting may be due to changes in manure physical/chemical characteristics, adsorption processes, or a reduction in bioavailability.


   Discussion
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 Materials and Methods
 Results
 Discussion
Conclusions
 REFERENCES
 
Degradation in compost is often correlated to soil or other matrix (i.e., manure, biosolids, sediments, etc.) degradation because the mechanisms are generally similar (e.g., Büyüksönmez et al., 1999). Carlson and Mabury (2006) measured a half-life of 21 to 24 d for chlortetracycline in soil. A similar half-life was reported in stockpiled fresh manure (low-intensity composting) for oxytetracycline, a structurally similar tetracycline antibiotic (De Liguoro et al., 2003). These data are consistent with the anticipated bioavailability, which is likely limited as a result of strong adsorption to solids, as indicated by high Kd values (Table 1). However, a much lower chlortetracycline half-life of 1 d for composting in this study is similar to the half-life of 3 d reported by Arikan et al. (2007) for composted manure. The lower half-life of chlortetracycline during composting and in the control treatment may be due to higher biological activity as a result of elevated temperatures or abiotic factors (i.e., nonbiological chemical transformations, environmental characteristics, etc.). Rose et al. (1996) found that oxytetracycline rapidly degraded in heated sterile water, indicating abiotic degradation processes. In their study, oxytetraycline half-life was 2, 15, and 120 min in water at 100, 80, and 62°C, respectively. Other studies have identified abiotic degradation of tetracycline (Søeborg et al., 2004), which suggests that at least some portion of chlortetracycline degradation during composting and stockpiling may be due to abiotic processes.

The half-lives of monensin and tylosin in soil and fresh manure are similar and range from 3 to 8 d (Elanco Products Company, 1989; De Liguoro et al., 2003; Ingerslev and Halling-Sørensen, 2001; Carlson and Mabury, 2006; Schlüsener and Bester, 2006), which are slightly lower than the values (11–23 d) observed in control and composted manure treatments in this study. The degradation behavior of sulfamethazine and similar sulfonamides is variable. Half-lives in soil range from 5 to 29 d (Kay et al., 2004; Wang et al., 2006; Accinelli et al., 2007). However, several studies in sewage sludge have found that sulfonamide degradation is preceded by a lag phase (6–50 d) due to microbial adaptation (Ingerslev and Halling-Sørensen, 2000; Pérez et al., 2005). Alternatively, studies in marine sediments have found limited or no degradation of sulfonamides (Samuelsen et al., 1994; Hektoen et al., 1995), which is consistent with results from this study. In contrast to chlortetracycline, sulfamethazine has been shown to be stable in heated water (Rose et al., 1995) and sterilized systems (Pérez et al., 2005; Accinelli et al., 2007).

Despite significant differences in temperature, mass, and nutrient characteristics, there were only slight differences in chlortetracycline, monensin, and tylosin degradation between the two composting treatments and the control (unmanaged composting). The lack of a significant difference among treatments suggests that stockpiling after mixing and achieving optimal water content would be sufficient for degradation of certain antibiotics. Because this study was conducted for only 35 d, the long-term effects of minimal manure management (unmanaged composting) on antibiotic degradation are not apparent. Minimal management would be a more practical and economical option for livestock producers as compared with labor-intensive management or high-cost vessel composting.


   Conclusions
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 Materials and Methods
 Results
 Discussion
 Conclusions
REFERENCES
 
Results from this study show that some level of manure management (mixing to optimum water content and then stockpiling) before land application can reduce levels of certain antibiotics. In this study, 35 d of thermophilic temperatures resulted in >99% reduction in chlortetracycline, whereas monensin and tylosin reduction ranged from 54 to 76%. There was no degradation of sulfamethazine in this study. The average half-lives for chlortetracycline, monensin, and tylosin were 1, 17, and 19 d, respectively. Despite significant differences in temperature, mass losses, and nutrient losses between the control, managed composting, and vessel composting treatments, there was no difference among the treatments on antibiotic degradation at the end of the trial period (22–35 d). Although this study was not designed to evaluate degradation mechanisms, there is strong evidence that biotic and abiotic factors contributed to antibiotic degradation during composting. More research is needed to determine the degradation of different antibiotic compounds in other manure types and management systems.


   ACKNOWLEDGMENTS
 
This research was supported in part by funds from the USDA-NRI program (grant number 2003-35102-13519) and the Rapid Agricultural Response Fund at the University of Minnesota. The authors thank Fred Hrbek and Terrance Yourchuck at the University of Minnesota Turkey Research Center at Rosemount, MN, for their on-site assistance with the composting project and Adam Loberg and Randy Robida from IDX Environmental, Inc. for setup and operation of the vessel composting unit.


   NOTES
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 NOTES
ABSTRACT
 INTRODUCTION
 Materials and Methods
 Results
 Discussion
 Conclusions
 REFERENCES
 
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   REFERENCES
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 ABSTRACT
 INTRODUCTION
 Materials and Methods
 Results
 Discussion
 Conclusions
 REFERENCES
 




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The SCI Journals Agronomy Journal Crop Science
Journal of Natural Resources
and Life Sciences Education		 Vadose Zone Journal
Soil Science Society of America Journal Journal of Plant Registrations The Plant Genome