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Carbon and nitrogen mineralisation and inactivation of the Cry1Ab protein in Bt maize (MON810) residues during composting

Abstract A study was carried out to determine the effects of composting Bt maize residues on carbon (C) and nitrogen (N) contents and activity of the Cry1Ab protein in the compost. Residues (leaf plus stem) of mature Bt maize (DKC 7815B) and its near-isoline (CRN 3505) were composted using 1 m3 wooden boxes. Temperature, C and N transformations, and activity of the Cry1Ab protein were monitored throughout the composting period. Residues of the hybrids used in this study composted similarly as shown by the temperature profiles, pH, C and N dynamics. The C:N ratios decreased from 33 and 23 for the Bt maize and near-isoline, respectively, to 15. Composting reduced the activity of the Bt protein in the residues, with a half-life of 3.3 d, to 22%, 7% and 3% of the initial level (90.5 ng g–1) in 7, 14 and 35 d, respectively, and approached undetectable levels after 63 d. The findings of this study suggest that Bt maize composts in the same way as conventional maize. The composting rapidly reduced the much higher C:N ratio of Bt maize and in the process eliminated the active Bt proteins in the residues, thus rendering them much safer for soil application.