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Transfer of transgenic crop toxins to aquatic ecosystems potentially widespread in the industrial Corn Belt of the U.S.

Monday, September 27th, 2010

Genetically modified organisms (GMOs) are back in the news.  A few days ago, NPR featured a couple of blog posts (here and here) considering whether the new GMO “supersized” salmon will be harmful to aquatic ecosystems.

A concern with GMOs is that—like the early adoption of pesticides—potential risks are being borne by the environment and consumers as we experiment with new species.  There’s a lot of potential for GMOs, and I hope that they all end up being harmless.  But there are potential downsides too that we are not able to assess very well at this point.  And we may be creating problems that we are not even aware of yet.

As more data come in, it’s not always an encouraging outlook.  A couple of recent examples:

Case #1: We saw a few months ago how weeds that were supposed to be eliminated by the agricultural herbicide, Roundup, are now evolving resistance to the chemical, meaning that Roundup-ready soybeans and other crops no longer work as designed.

Case #2:  In this week’s Early Edition of the Proceedings of the National Academy of Sciences, Jennifer Tank and colleagues examined what happens to transgenic corn residue (old crop parts left on fields that are not harvested).  One of the main transgenic varieties of corn is known as “Bt corn.”  Bt stands for the name of a microbe—Bacillus thuringiensis—that makes a protein toxin that destroys the functioning of guts in some insects.  Scientists have figured out how to move the Bt gene, and hence Bt toxin manufacturing capacity, from the bacteria to corn plants, thereby conferring general insect herbivore resistance to this crop (the main pest being the European corn borer).

This team asked:  What happens when corn stalks, cobs, and leaves end up in streams and rivers throughout the Midwest?  Their answer is eye-opening:

Widespread planting of maize throughout the agricultural Midwest may result in detritus entering adjacent stream ecosystems, and 63% of the 2009 US maize crop was genetically modified to express insecticidal Cry proteins derived from Bacillus thuringiensis. Six months after harvest, we conducted a synoptic survey of 217 stream sites in Indiana to determine the extent of maize detritus and presence of Cry1Ab protein in the stream network. We found that 86% of stream sites contained maize leaves, cobs, husks, and/or stalks in the active stream channel. We also detected Cry1Ab protein in stream-channel maize at 13% of sites and in the water column at 23% of sites. We found that 82% of stream sites were adjacent to maize fields, and Geographical Information Systems analyses indicated that 100% of sites containing Cry1Ab-positive detritus in the active stream channel had maize planted within 500 m during the previous crop year. Maize detritus likely enters streams throughout the Corn Belt; using US Department of Agriculture land cover data, we estimate that 91% of the 256,446 km of streams/rivers in Iowa, Illinois, and Indiana are located within 500 m of a maize field. Maize detritus is common in low-gradient stream channels in northwestern Indiana, and Cry1Ab proteins persist in maize leaves and can be measured in the water column even 6 mo after harvest. Hence, maize detritus, and associated Cry1Ab proteins, are widely distributed and persistent in the headwater streams of a Corn Belt landscape.

Who cares?  Streams and rivers are the breeding grounds to many insect species, including dragonflies, mayflies, and damselflies.  If there are toxins floating in these aquatic ecosystems that are good at killing insects, there is risk of disrupting food webs, including potential changes to bird species as well as many important recreational and sport fish that dine on insects:

Once maize detritus enters stream channels, this carbon source degrades rapidly via a combination of microbial decomposition, physical breakdown, and invertebrate consumption, and that energy may fuel stream food webs. Maize detritus in agricultural streams decomposes in ∼66 d …. Therefore, the material that we found during our synoptic survey had entered these streams relatively recently. Maize detritus is rapidly colonized by stream-dwelling invertebrates, and growth rates of invertebrates feeding on nontransgenic decomposing maize are comparable to those feeding on the deciduous leaf litter commonly found in forested streams

Perhaps this means that the Bt toxins might break down quickly and pose less harm? Doesn’t look like it:

Our data demonstrate that long after harvest, Cry1Ab is present in submerged Bt maize detritus; thus, stream organisms may be exposed to Cry1Ab for several months.

It’s also interesting to learn that low or no-till conservation tillage practices may exacerbate the corn residue inputs because greater material left on fields is susceptible to washing away:

The dried detritus left on fields after harvest, as part of conservation tillage, enters headwater streams as a result of surface runoff and/or wind events occurring throughout the year. During heavy precipitation, overland flow is the likely mechanism transporting this material to stream channels.

It may not even be a matter of leaving less residue; the toxins also appear to be draining through the soils:

Our results from tile drains indicate that tiles may be a mechanism by which Cry1Ab leached from detritus on fields or from soils can be transported to streams.
Cry1Ab released from root exudates or decaying maize detritus moves vertically through soils and can be detected at the base of 15-cm-long soil profiles for up to 9 h.

Their conclusion?  An illustration of how little we know at this point:

The question of whether the concentrations of Cry1Ab protein we report in this study have any effects on nontarget organisms merits further study.

Jennifer L. Tank, Emma J. Rosi-Marshall, Todd V. Royer, Matt R. Whiles, Natalie A. Griffiths, Therese C. Frauendorf, and David J. Treering (2010). Occurrence of maize detritus and a transgenic insecticidal protein (Cry1Ab) within the stream network of an agricultural landscape Proceedings of the National Academy of Sciences : 10.1073/pnas.1006925107


Photo credit: snake.eyes

8 Responses to “Transfer of transgenic crop toxins to aquatic ecosystems potentially widespread in the industrial Corn Belt of the U.S.”

  1. RAH says:

    “Their conclusion? An illustration of how little we know at this point:” is very accurate. A read of their analytical methods finds that they claim a detection limit of 6 parts per trillion which is far below that claimed by the ELISA kit manufacturer. Extending this limit so low demands some rigorous validation which is not reported in the paper. Indeed they report using distilled water as the matrix blank which is osmotically and compositionally very different from stream water. While the results they report may be accurate, they are more likely false-positives due to many factors not controlled in their experiments. The quality of this paper is at least consistant with that of their previous PNAS paper – very poor. I would expect to see letters to the ditor by immunoassay experts in the near future.

  2. RedDirt says:

    There will be many reasons for countries to go to war for & one of the most important will be control over water for its economy (not necessarily for its citizens).

  3. Old Film Fan says:

    RAH, as a sun god you should know the truth: “GM maize-fed rats were compared first to their respective isogenic or parental non-GM equivalent control groups, followed by comparison to six reference groups, which had consumed various other non-GM maize varieties. According to the authors, “Our analysis clearly reveals for the 3 GMOs new side effects linked with GM maize consumption, which were sex- and often dose-dependent. Effects were mostly associated with the kidney and liver, the dietary detoxifying organs, although different between the 3 GMOs. Other effects were also noticed in the heart, adrenal glands, spleen and haematopoietic system. We conclude that these data highlight signs of hepatorenal toxicity, possibly due to the new pesticides specific to each GM corn.”

    In other words, it kills black rats. In addition, it can’t be washed off. It is inside every cell.

    If you have eaten “Attribute” brand canned corn, you are eating Bacillus thuringiensis (Bt) toxin, and it is attacking your endocrine system as surely as it does Rattus Rattus Norwegicus. And furthermore, this toxin is now polluting our meat supply (it lastst 45 days in beef).

    Of course, the greatest danger is that it is introduced into regular products, such as corn oil and corn syrup.

    No blame.

  4. john Thompson says:

    The insecticide in GM crops (Bt) causes a strong immune response in any insect that can
    survive its toxicity. Any immune response in any insect causes cognitive impairment of
    that insect. Bees are specifically prone to memory loss from an immune response in winter,
    as Bees can get no protein from pollen in winter and Pollen protein is used by Bees for
    their immune response and also used by Bees to create their memory. So as a result of the
    immune response to GM Bt toxin, Bees use up all their protein reserves and have no protein
    reserves left to form a memory and so the Bees loose their memory can not remember where
    their own Bee hive is located. Thus Colony Collapse Disorder is created, Bees disappear
    from the hive and no dead Bees are found. And CCD was only seen after GM Bt was widely

  5. Thomas Brown says:

    What if the GM Bt toxin gene floats down the river and because it is highly reactive due to the “sticky ends” attached to the gene, gets inserted into single celled plants common in sea water known as phytoplankton. Almost all sea life except for some arcane sulfide vent creatures ultimately can trace their food energy from phytoplankton which is converted energy from the sun. How is that going to play out in the food chain? The bee colony collapse disorder is something that we can see because it’s in our faces. It doesn’t take much to have a disaster from unintended consequences of science that has not been toughtfully applied to massive parts of the envioronment.

  6. GerneyLee Carter says:

    I have determined that agriculture in and of itself am aberrant…everyday I accumulate more to support my opinion/theory/hypothesis. Most obviously it supports over population…sigh! I have no answers…I only see the problems pretty darn clearly.

    see this too:

    mixed together: GREAT!

  7. [...] Transfer of transgenic crop toxins to aquatic ecosystems potentially widespread in the industrial Corn Belt of the U.S. October 7, 2010 by mdnelson From Global Change [...]

  8. [...] on GM crops, it could be done with a mix of hybrid crop varieties that doesn’t risk the potential environmental side effects of Bt corn or other unexpected outcomes of GM crops.  This is a major value judgment.   Does having one GM [...]


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