Submitted to: Journal of Hazardous Materials
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/12/2008
Publication Date: 8/15/2008
Citation: Arikan, O., Mulbry III, W.W., Rice, C. 2008. Management of Antibiotic Residues from Agricultural Sources: Use of Composting to Reduce Chlortetracycline Residues in Beef Manure from Treated Animals. Journal of Hazardous Materials. 164:483-489.
Interpretive Summary: The use of antibiotics as growth promoters and therapeutic agents is widespread in the animal production industry. However, there is a growing concern about the potential impact of antibiotic residues from such agricultural sources on the development of antibiotic-resistant bacteria. Previous studies have shown that between 17-76% of antibiotics administered to animals are excreted via urine and feces in unaltered form and as metabolites. Land application of manure as a supplement to fertilizer is a common practice in many countries. It is therefore likely that when animal manure applied to a land, antibiotic residues can find their way into the receiving environment. Chlortetracycline (CTC) is an antibiotic used in livestock production that is active against a wide range of gram-positive and gram-negative bacteria. Treatment of manure containing CTC is one possible means of reducing the amount of this compound that is ultimately released into the environment. Manure composting is a well-described approach for stabilization of nutrients and reduction of pathogens and odors. In addition, composting has been shown to be effective in reducing relatively persistent organic compounds such as pharmaceuticals and personal care products. The objective of this study was to determine the effect of composting on CTC residues in manure from medicated calves. Results from laboratory scale composting experiments showed that concentrations of CTC and its metabolites decreased more than 99% in 30 days in manure/straw/woodchip mixtures that reached normal composting temperatures (55 C). In comparison, concentrations of CTC and its metabolites decreased about 40% in 30 days in manure/straw/woodchip mixtures that were incubated at room temperature (25 C). Results from experiments using sterilized manure/straw/woodchip mixtures showed that the decreases in CTC concentrations at 25 C and 55 C were largely due to non-biological processes such as adsorption to organic material rather than to degradation by microorganisms.
Technical Abstract: Chlortetracycline (CTC) is one of only ten antibiotics licensed in the U.S.A. for use as a growth promoter for livestock. The widespread use of CTC may contribute to development of antibiotic-resistant bacteria. The objective of this study was to determine the effect of composting on the fate of CTC residues found in manure from medicated animals. The effect of CTC residues on composting was also investigated. Five beef calves were medicated for five days with 22 mg/kg/day of CTC. Manure samples collected from calves prior to and after medication were mixed with straw and woodchips, and aliquots of the subsequent mixtures were treated in laboratory composters for 30 days. In addition, aliquots of the CTC-containing mixture were incubated at 25 C or sterilized followed by incubation at 25 C and 55 C (composting temperature). The presence of CTC did not affect composting processes. Levels of CTC in the composted mixture (CM) and sterilized mixture incubated at 55 oC (SM55) decreased 99% and 98% (from 69 µg/g dry weight (DW) to 0.5 and 1.3 µg/g DW) in 30 days. In contrast, levels of CTC in room temperature incubated (RTIM) and sterilized mixture (SM25) decreased only 40% (from 69 µg/g DW to 42 µg/g DW) after 30 days. The concentration of the CTC epimer, 4-epi-chlortetracycline (ECTC), declined 99% and 98% (from 44 µg/g DW to 0.6 and 1.6 µg/g DW) in CM and SM55 respectively, while the levels of ECTC reduced 62% and 41% in RTIM (to 17 µg/g DW) and SM25 (to 26 µg/g DW), respectively. Concentrations of the CTC metabolite, iso-chlortetracycline (ICTC), in CM and SM55 decreased more than 99% (from 12 µg/g DW to below quantitation limit of 0.3 µg/g DW). ICTC levels in RTIM and SM25 decreased 80% (to 4 µg/g DW). For CTC, ECTC and ICTC, sterilized mixtures, SM55 and SM25, followed similar patterns with CM and RTIM, respectively. This suggests that the decrease of CTC concentrations during composting is largely due to abiotic processes and is temperature dependent.