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Genetically inserted insecticide contaminates U.S. waterways

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Add another compound to the long list of agricultural pollutants in the nation’s streams, rivers and waterways: the Bacillus thuringiensis or Bt toxin, a protein crystal known as Cry1Ab that kills caterpillars and other agricultural pests. A wide variety of crops, including 63 percent of the corn planted in the U.S. in 2009, have been genetically engineered to build the bacterial protein in their leaves and stems.

Those roots and stems are apparently washing into the waterways of the Midwest; 86 percent of 217 streams in Indiana surveyed by scientists contained such detritus. And, according to the results of that survey published online September 27 in Proceedings of the National Academy of Sciences, 23 percent of the streams had the Bt toxin floating in the water—six months after harvest.

All of the contaminated streams lay 500 meters or less from a corn field and, based on current maps of lands used for agriculture, the researchers estimate that 91 percent of waterways in the Midwest—Iowa, Illinois, Indiana—are within that distance from a corn field. The finding may also be the result of a practice known as "no-till" farming, in which the unused portions of the crop are left on the fields to minimize erosion, though the crop waste itself seems to end up in the adjacent streams.

Of course, these streams ultimately feed one of the great river systems of the planet—the Mississippi and Missouri river basin. Ultimately, those rivers terminate in the Gulf of Mexico, where runoff of agricultural fertilizers promotes algal blooms that end up creating vast "dead zones" of seawaters devoid of oxygen. In fact, the U.S. Geological Survey found that levels of such fertilizer runoff have remained the same or even increased since the 1990s in a recent analysis.

It remains unclear what impact the Bt toxin may be having in any of these aquatic ecosystems, if any. But it is clear now that the insecticides genetically engineered into plants—like their manufactured chemical counterparts—are capable of traveling with the rain from field to stream.

Image: Courtesy of Google Maps

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  1. 1. javier_and 4:41 pm 09/28/2010

    I already have searched for the original paper in PNAS but in the last two issues I found nothing about this information about Bt toxins. Could you please specify which issue corresponds to the information mentioned in SciAm?
    thank you

    Link to this
  2. 2. dbtinc 4:44 pm 09/28/2010

    … and why should we be concerned?

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  3. 3. londan123 5:38 pm 09/28/2010

    Thanks for the information.

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  4. 4. javier_and 6:54 pm 09/28/2010

    we should be concerned because, despite all the pollutants that are already in the environment and we don’t know the effects on humans, wildlife and ecosystems, we are creating new ones that may derive in environmental and health problems.

    Link to this
  5. 5. dbiello 9:11 am 09/29/2010

    Here’s the link, which is also in the story:

    Occurrence of maize detritus and a transgenic insecticidal protein (Cry1Ab) within the stream network of an agricultural landscape

    As for why we should be concerned, there’s no alarm as of yet. But it is surprising they were able to detect the Cry1Ab six months after harvest in the water given that the toxin is supposed to biodegrade quickly. So more study is needed to see what, if any, impact the toxin might have on aquatic insects and why the toxin is persisting in these cases (possibly sheer volume of detritus from U.S. corn fields?)

    Link to this
  6. 6. MidWest101 2:05 pm 09/29/2010

    It is my understanding that Bacillus thuringiensis is a naturally occuring soil bacteria. If that is true, large amounts of the toxin have been flowing into the water for quite some time. I am going to need a lot more than this to start woring about Bt in the water.

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  7. 7. Spiff 3:42 pm 09/29/2010

    And what about the poop from beef cattle and cows that have been injected with hormones and steroids…Science has made it possible to live longer, the pay back is that most of us will die of a cancer rather then from "old age"…

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  8. 8. Tom J 4:00 pm 09/30/2010

    So once we cure cancer, we’re golden!

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  9. 9. Tom J 4:04 pm 09/30/2010

    My problem with this study is that there doesn’t seem to be any historical baseline as to the amount of Bt toxin that is naturally present in the water. They might be detecting the natural Bt residue from colonies of soil bacteria.

    Link to this

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