1. THE INCIDENT:
In an article of PNAS (Proceedings of the National Academy of Sciences, USA) it is reported that aquatic organisms are potentially harmed by residues and toxins of Bt maize, the paper does not convince in many aspects, as detailed below in a letter to the editor.
Rosi-Marshall, E.J., Tank, J.L., Royer, T.V., Whiles, M.R., Evans-White, M., Chambers, C., Griffiths, N.A., Pokelsek, J., & Stephen, M.L. (2007)
Toxins in transgenic crop byproducts may affect headwater stream ecosystems. Proceedings of the National
Academy of Sciences of the United States of America, 104, pp 16204-16208
<Go to ISI>://WOS:000250128800043 10.1073/pnas.0707177104 AND
http://www.pnas.org/cgi/content/abstract/0707177104v2 AND http://www.botanischergarten.ch/Bt/Rosi-Marschall-Bt-Aquatic-2007.pdf
The abstract:
“Corn (Zea mays L.) that has been genetically engineered to produce the Cry1Ab protein (Bt corn) is resistant to lepidopteran pests. Bt corn is widely planted in the mid-western United States, often adjacent to headwater streams. We show that corn byproducts, such as pollen and detritus, enter headwater streams and are subject to storage, consumption, and transport to downstream water bodies. Laboratory feeding trials showed that consumption of Bt corn byproducts reduced growth and increased mortality of non-target stream insects. Stream insects are important prey for aquatic and riparian predators, and widespread planting of Bt crops has unexpected ecosystem-scale consequences.”
(Rosi-Marshall et al., 2007)
In chapter 6 read about the most recent publications of an author group, lead previously by Prof. Galen Dively (Jensen et al., 2010; Swan et al., 2009d) and others, they contain rebuttals of the Rosi-Marshalls claims, mainly on grounds of a better baseline comparison of complex factors influencing aquatic organisms.
2. Summary
The news of potential harm of Bt crops to aquatic organisms has spread rapidly on many websites, Greenpeace also supports the arguments of the authors, and the former EU commissioner for the environment Stavros Dimas opposed the new maize traits from Pioneer and Syngenta on grounds of the precautionary principle and referring to a comment by Greenpeace on the above study: . http://uk.reuters.com/articlePrint?articleId=UKL2524238420071025
The critique can be summarized as follows (more details and literature below):
There is extensive literature demonstrating that in the realistic concentrations Bt toxins do not harm aquatic organism.
The authors extrapolated in a problematic way from a laboratory test to a field system based on a single study.
The Bt source of the study is not specified, there is a possibility that Dipel, a Bt spray is also involved and there are several different Bt toxins which could be involved and even the natural Bt toxin of soil (bacteria) could have influenced the results.
And in addition, the Bt maize involved in the study is not disclosed and later publications have shown that differences in various hybrid traits might influence the results more than the presence or absence of Bt-toxins in the litter. A clear baseline is lacking and even other pesticides might be involved.
In two recent publications of (Swan et al., 2009d) and (Jensen et al., 2010) the paper of Rosi-Marshall has been contradicted in several major statements.
Summarized, it can be said that the study of Rosi-Marshall lacks the quality which is needed for such far reaching conclusions. Despite this, the study has been heavily promoted by groups opposing GMO crops without the necessary scientific justification
for citations and more text see: http://www.ask-force.org/web/AF-3-Aquatic-Bt/AF-3-Aquatic-Bt-toxins-20100423-web.pdf
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