GE crops with Bacillus thuringiensis (Bt) genes suspected to harm soil ecology
(The text below is an excerpt from Seedling, march 1999 vol.16, no 1)
"Typically, toxins in naturally-occurring Bacillus thuringiensis (Bt) bacteria, and sprays made from them, exist in an inactive form, which becomes activated once ingested by the target insect.
By contrast, the toxins in many Bt crops are already in the active form. Researchers from New York University, including the renowned soil ecologist Guenther Stotsky, found that unlike natural Bt, these active toxins do not disappear when added to soil, but become rapidly bound to soil particles, and are not broken down by soil microbes. This contradicts what Monsanto scientists have been soying about soil persistence of Bt toxin from their Bt crops.
The researchers contend that engineered Bt toxins could built up in the soil, killing Bt sensitive soil organisms and increasing selection pressure for resistance to develop.".
ReferencesJ. Koskella and G. Stotzky. "Microbial Utilization of Free and Clay-Bound Insecticidal Toxins from Bt and Their Retention of Insecticidal Activity after Incubation with Microbes," Applied and Env. Microbiology, Sept. 1997, p. 3561-3568.
H. Tapp and G. Stotzky, "Persistence of the Insecticidal Toxin from Bt subsp. Kurstaki in Soil," Soil Biology and Biochemistry, Vol. 30, No. 4, p. 471-476., 1998,
Comment by PSRASTThe use of GE crops with Bt toxin genes is widespread. These genes make the crops resistant to important pests. Due to these genes, the Bt toxin is produced in every part of the plant, so when the parts not harvested decompose, considerable amounts of the toxin may reach the soil.
Dr Charles Benbrook, former Executive Director of the Board on Agriculture for the US National Academy of Sciences has commented: "Compared to the volume of Bt in the soil in a conventional agroecosystem, the quantity of Bt entering the soil in corn stalks and stover must be enormous... Remarkably millions of acres of Bt GM varieties have been allowed to be grown in the US with little, if any, research being carried out as to the long term effect on soil fertility of such potentially toxic plant residue material (i.e when incorporated into soils post-harvest in preparation for the next crop). That this fundamental question has been overlooked is symptomatic of modern systems of agriculture generally, which frequently pay little regard to the fundamental role microbial activity plays in maintaining genuine soil fertility." For more about the ecology of soil microorganisms and soil fertility, see "Genetically Engineered Crops and Soil Fertility".
There are at least 7 varieties of Bt Corn, including Yieldgard and Bt-Xtra and an unnamed strain from Monsanto, KnockOut and Bt11 from Novartis, NatureGuard from Mycogen and an unnamed variety from Hoechst/Agrevo. There are 2 varieties of Bt Cotton from Monsanto including the widely used Bollgard strain. Two Bt potato strains are approved, New Leaf and New Leaf Plus, both from Monsanto.
In the US, GE corn crops covered about 25% (20 million acres) of the total corn acerage in 1998. GE cotton covered 45% (6 million acres) of the total cotton acerage. A considerable part of these crops had Bt toxin genes.
Therefore, if soil ecology is damaged due to Bt toxins released into the soil from GE crops, fertility problems may ensue in a significant part of American soils.
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