Research Article Received: 22 September 2009 Revised: 6 November 2009 Accepted: 16 November 2009 Published online in Wiley Interscience: (www.interscience.wiley.com) DOI 10.1002/jsfa.3863 Biodegradation of genetically modified seeds and plant tissues during composting Tim Reuter, a Trevor W Alexander, a Weiping Xu, b,c Kim Stanford b and Tim A McAllister, a∗ Abstract BACKGROUND: The increasing global market of genetically modified (GM) crops amplifies the potential for unintentional contamination of food and feed with GM plants. Methods proposed for disposal of crop residues should be assessed to prevent unintended distribution of GM materials. Composting of organic material is inexpensive and location-independent. The objective of this study was to determine the effectiveness of composting for disposal of GM plants in terms of reducing seed viability and promoting the degradation of endogenous as well as transgenic DNA. RESULTS: Duplicate samples of corn kernels, alfalfa leaves, and GM canola seeds, meal and pellets were sealed in porous nylon bags and implanted in duplicate 85 000 kg (initial weight) feedlot manure compost piles. Samples were collected at intervals over 230 days of composing. Canola seeds and corn kernels were not viable after 14 days of composting with temperatures in the piles exceeding 50 ◦ C. In all samples, PCR analyses revealed that plant endogenous and transgenic fragments were substantially degraded after 230 days of composting. Southern blotting of genomic DNA isolated from canola seeds identified differences in the persistence of endogenous, transgenic, and bacterial DNA. CONCLUSION: Composting GM and non-GM plant materials with manure rendered seeds non-viable, and resulted in substantial, although not complete, degradation of endogenous and transgenic plant DNA. This study demonstrates that composting could be effective for disposing of GM crops in the event of their inadvertent entry into the food or feed chain. Copyright c  2010 Crown in the right of Canada. Published by John Wiley & Sons, Ltd Keywords: canola; compost; corn; DNA; plant; seed; transgenic; viability INTRODUCTION Genetically modified (GM) organisms are playing an increasingly important role in both the medical 1 and agricultural fields. 2 The global market for GM crops in agriculture has increased 50-fold over the last decade; at present, these crops are grown on ap- proximately 100 million ha worldwide. 3 Despite widespread use of GM crops in agriculture and numerous reports of their equiv- alency to non-GM crops, 2 several countries have not approved their use, and acceptance of GM products by consumers remains tentative. 4,5 Some countries have implemented mandatory label- ing laws requiring that foods containing GM plant material be clearly identified. 6 Importation of crops is generally banned if, within a shipment, a GM trait exceeds a set threshold. However, many GM crops are exported, raising the possibility that GM plant materials may inadvertently enter countries in which regulatory approval for their use has not been granted. 7 In other instances, GM crops approved only for animal feed may end up in food destined for human consumption, as was the case when StarLink  corn was used in the manufacture of tacos. 8,9 Although the importation of unapproved large volumes of GM crops is rare, increasing market volumes and the coexistence of GM crops with conventional and organic crops raises the probability of cross-contamination and/or the spread of genetically modified crops into pristine environments. Consequently, the need exists for a rapid and economical method by which to dispose of GM plant material that enters unintended markets. Composting has been widely used as a means of accelerating the decomposition of organic matter 10 and previous research with laboratory-scale composters has shown that recombinant DNA in corn is degraded during the composting process. 11 The objective of this study was to further characterize the impact of composting on the decomposition of plant DNA and on the viability of both GM and non-GM seeds in field-scale composting systems. MATERIALS AND METHODS Compost construction and sampling Duplicate compost structures (east and west) were built at the Lethbridge Research Centre, Alberta, using the method described previously. 12 The compost matrix was contained in a bunker ∗ Correspondence to: Tim A McAllister, Agriculture and Agri-Food Canada, Leth- bridge Research Centre, P.O. Box 3000, Lethbridge, Alberta, T1J 4B1, Canada. E-mail: tim.mcallister@agr.gc.ca a Agriculture and Agri-Food Canada, Lethbridge Research Centre, P.O. Box 3000, Lethbridge, Alberta, T1J 4B1, Canada b Alberta Agriculture and Rural Development, Agriculture Centre, Lethbridge, Alberta, T1J 4V6, Canada c Department of Bioscience and Biotechnology, Dalian University of Technology, Dalian 116024, China J Sci Food Agric (2010) www.soci.org Copyright c  2010 Crown in the right of Canada. Published by John Wiley & Sons, Ltd