Jul 25, 2011

Research Projects

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Does Bt protein from GM maize enter fields through slurry spreading?

(2007 – 2008) Bayerische Landesanstalt für Landwirtschaft, Institut für Pflanzenbau und Pflanzenzüchtung

Topic

The spreading of slurry from cows fed on genetically modified Bt maize (MON810) could cause both the Cry1Ab DNA inserted into the plant and the Bt protein to re-enter fields and end up in vegetation and in the soil. These compounds can break down in chemical and microbial processes in the soil, but they can also bind to organic or inorganic soil constituents.

This project investigated whether, and in what quantities, the Bt protein and Cry1Ab DNA enter vegetation and soil as a result of slurry spreading. It traced the breakdown of the Bt protein throughout the slurry management process of a dairy farm that feeds Bt maize to its cattle: from maize plant to animal feed, to slurry, to soil and vegetation (grassland and maize) on the fertilized plots.

Summary

• There were no indications of Cry1Ab DNA from MON810 Bt maize entering farmland soil through slurry.
• The Bt protein levels fell progressively as a result of processing and breakdown: from the harvested maize to the feed and slurry.
• Very small quantities of the Bt protein were detected in the slurry.
• None of the soil samples from the plots treated with slurry from animals fed on Bt maize were found to contain Bt protein.
• No Bt protein was found in the cut grass or in non-GM maize plants grown on the slurry-treated plots.

Experiment description

The project was a collaboration between the Bavarian State Research Centre for Agriculture (LfL) and Technische Universität München (TUM).

The research was conducted in 2007. Two groups of five Simmental dairy cows were given feed containing either Bt maize or a corresponding diet consisting of maize from the isogenic parent variety. Over a period of six days the slurry was collected separately and stored. At predefined times, slurry was taken from the storage tanks and spread on grassland plots and on trial plots on which Bt maize and maize of the isogenic parent variety was growing (Grub and Finsing sites).

Soil samples were taken from these treated plots, the grass was cut repeatedly and the maize plants were harvested and chopped up.

Specific detection methods were developed and validated during the project for the analysis of the various agricultural samples (feed, slurry, soil, harvested crop). PCR was used to detect Cry1Ab DNA. A very sensitive ELISAtest was used to measure the quantity of Cry1Ab Bt protein.

Results

While Cry1Ab DNA from MON810 Bt maize was found in the feed, it was no longer detectable in the slurry samples from cattle fed on Bt maize, once it had passed through the gastrointestinal system. There were therefore no indications of Cry1Ab DNA entering farmland soil through slurry.

The Bt protein level fell progressively: from the harvested maize to the feed and slurry. Most of the Bt protein was broken down when the Bt maize plants were processed to make animal feed. Only 2.6 per cent of the Bt protein from maize was detected in the feed. Minimal residues of Bt protein were found in the slurry, in the region of 20 nanograms per gram of slurry.

None of the soil samples from the plots treated with slurry from animals fed on Bt maize were found to contain Bt protein. Accordingly, no Bt protein was found in the plants harvested from the trial plots (cut grass and isogenic maize plants).

The Bt protein proved less stable than the total protein metabolized in the agricultural processes under investigation. Western Blot analyses of the Bt protein from maize plants, feed and slurry showed that the Bt protein molecule is progressively broken down into smaller protein fragments.