|Letter attacking PNAS study "misleading" (19/11/2007)|
NOTE: Below Dr. Doug Gurian-Sherman, Senior Scientist at the Union of Concerned Scientists and former biotech specialist at the U.S. government's Environmental Protection Agency (EPA), comments on a recent letter attacking a study published by the journal, Proceedings of the National Academy of Sciences (PNAS).
The Rosi-Marshall et al study - funded by the National Science Foundation - found consumption of Bt corn byproducts produced increased mortality and reduced growth in caddisflies, an important food resource for higher organisms like fish and amphibians.
The letter attacking the study is from the 'usual suspects' - Alan McHughen, Henry Miller, Klaus Ammann, C. Kameswara Rao, Ingo Potrykus, Piero Morandini, Chris Leaver, S. Shantharam, Mark Sears, and C. S. Prakash. With the exception of Sears, none seems to have any especial expertise in the area they're commenting on, and nearly all can be found in the GM Watch profiles (or by searching at www.gmwatch.org) of ardent GM promoters.
As you know, the recent paper in PNAS that shows possible harm to stream insects was attacked by a group of scientists in a letter to the journal editor. Most of the points that they raise in their letter are misleading, even while some of them are technically correct. Because of the subtleties involved, I have written rebuttal points that I sent to some friends. I thought that they may be useful to others. My points are in caps following the relevant sections of the letter written by the pro-GE scientists.
Comments and letter to the editors of PNAS
A consortium of scientists signing this comment in a letter to the editors has analyzed the paper and came to critical conclusions, which seriously question the conclusions of the paper.
We call your attention, in particular, to the following:
1) There is extensive evidence in the literature that corn pollen produced by currently available Bt corn varieties contain extremely low amounts of Bt toxin. This was shown in a series of six papers by top scientists published in PNAS after the Losey Bt corn pollen-Monarch debacle, an intensive and time-consuming effort to try to set the science straight (1). How many busy scientists and how much scarce money will we need to divert to calm this new scare?
IT IS SAD THAT THESE SCIENTISTS, ONE OF WHOM (MARK SEARS), WAS APPARENTLY HAPPY TO RECEIVE FUNDING TO PARTICIPATE IN THE MONARCH STUDIES (MAYBE HE WOULD SAY IT WAS HIS DUTY!), CANNOT APPRECIATE THE VALUE OF THE ADDED AGROECOLOGICAL KNOWLEDGE THAT THOSE STUDIES CONTRIBUTED. IN ADDITION (SPEAKING AS AN EPA SCIENTIST WHO WAS THERE AT THE TIME) THOSE STUDIES WERE NECESSARY TO INFORM EPA ABOUT ACTUAL RISKS FROM Bt CROPS IN THE FIELD. THE LOSEY PAPER ON MONARCHS WAS A PERFECTLY REASONABLE ONE. IN ANY CASE, THERE ARE SEVERAL ASPECTS OF THE MONARCH BUTTERFLY INCIDENT THAT ARE MISREPRESENTED HERE. FIRST, THERE WAS IN FACT A VARIETY OF Bt CORN, Bt176, THAT COULD INDEED KILL MONARCH BUTTERFLIES IN THE FIELD DUE TO HIGH LEVELS OF Bt TOXIN IN ITS POLLEN. IT WAS FORTUITOUS (I.E. HAVING NOTHING TO DO WITH EPA RISK ASSESSMENT) THAT THIS VARIETY WAS NEVER GROWN ON MORE THAN ABOUT 5% OF U.S. CORN ACRES, AND THEREFORE DID NOT HAVE A MAJOR IMPACT. THIS VARIETY WAS NOT RE-REGISTERED AFTER THESE RESULTS WERE DISCOVERED. SECOND, THERE WAS ENOUGH TOXIN IN THE POLLEN IN THE OTHER MORE WIDELY-PLANTED VARIETIES (MON810 AND Bt11) TO KILL MANY MONARCHS - UP TO ABOUT 24% ACCORDING TO A LATER STUDY (DIVELY ET AL. 2004). THE REASON THAT MORE MONARCHS WERE ACTUALLY NOT THREATENED WAS THAT THE CATERPILLARS WERE USUALLY NOT PRESENT IN CORN FIELDS WHEN POLLEN FROM CORN WAS PRODUCED. THESE DATA WERE NOT KNOWN BEFORE THE FIELD STUDIES REFERRED TO BY THESE LETTER WRITERS, AND THEREFORE ACTUAL RISKS TO MONARCHS WERE NOT WELL KNOWN BEFORE THOSE STUDIES WERE CARRIED OUT. THAT THE LETTER WRITERS SUGGEST THAT THESE STUDIES WERE A WASTE OF TIME REVEALS THAT THEY REALLY DON'T HAVE AN INTEREST IN MAKING SURE THAT THE RISKS FROM GE CROPS ARE MINIMAL.
2) The authors extrapolated from a laboratory test to a field system based on a single study. Such extrapolation is problematic to begin with; not only did the authors lack the statistical confidence necessary for a valid extrapolation, in another venue (2) they reported they did not find these effects in the field, a salient fact not mentioned in the PNAS paper. This discrepancy should have been disclosed and discussed. In addition, earlier relevant studies concluded that Bacillus thuringiensis (Bt) endotoxin concentrations in aquatic systems are extremely low and are metabolized rapidly in water (3,4).
THEY DID NOT EXTRAPOLATE TO THE FIELD. THEY NOTED AT LEAST FOUR TIMES IN THEIR PAPER THAT THEIR RESULTS 'MAY' HAVE IMPLICATIONS FOR THE FIELD. THIS TERM OF CONTINGENCY CLEARLY IS USED TO QUALIFY THE POSSIBLE FIELD IMPLICATIONS. THE EARLIER 'RELEVANT' STUDY (( http://www.benthos.org/database/allnabstracts.cfm/db/Columbia2007abstracts/id/370 , ONLY AN ABSTRACT) WAS ONLY ABOUT POLLEN - IT DID NOT CONSIDER LEAVES! THE CURRENT STUDY USED HIGHER LEVELS OF POLLEN, AND THE AUTHORS ACKNOWLEDGED THAT THE POLLEN AMOUNTS WERE HIGHER THAN WOULD OFTEN BE FOUND IN STREAMS. HOWEVER, THE MORE RELEVANT ISSUE IS EXPOSURE TO LEAVES AND OTHER SIMILAR MATERIAL BECAUSE 1) IT WAS FOUND TO BE PRESENT IN STREAMS AT MUCH HIGHER LEVELS THAN POLLEN, AND 2) THE AMOUNT OF Bt TOXIN IN LEAVES AND SIMILAR PLANT TISSUES IS MANY-FOLD HIGHER THAN IN POLLEN. AS TO THE OTHER CITED PAPERS, IT IS NOT UNCOMMON FOR DIFFERENT RESEARCH USING DIFFERENT METHODS TO GET DIFFERENT RESULTS. IT SHOULD BE NOTED HOWEVER, THAT EVEN THOSE OTHER STUDIES FOUND MEASURABLE Bt TOXIN IN RIVERS.
3) The title implies transgenic crops are the only source of Bt toxins, but endotoxins in commercial Bt insecticides such as Dipel, Xentari, Foray, and Thuricide are also used by farmers, including organic farmers, to control insects, and in some areas intensively If the authors are measuring the effect of Bt toxin at all, how do they know the toxin comes from the transgenic Bt crops rather than from these organic Bt insecticides? If they lack data to distinguish the sources, isn't the term `transgenic' in the title simply gratuitous and sensationalistic?
THE LAB EXPERIMENTS USED Bt CORN, NOT Bt M