FYI - Bt Risk Negligible?

Danfosha at Danfosha at
Mon Dec 3 12:57:24 EST 2001


ISIS Report, 12 November, 2001

Bt Risk Negligible?

The United States Environment Protection Agency has renewed the registration 
of Bt corn based on new studies that claim the impact of Bt-corn pollen on 
monarch butterfly is "negligible". But <A HREF="mailto:m.w.ho at">Dr. Mae-Wan Ho</A> and <A HREF="mailto:jcummins at">Prof. Joe Cummins</A> 
say that is playing fast and loose with scientific evidence.

When John Losey and colleagues in Cornell University published their findings 
that Bt-corn pollen harmed monarch butterflies, the concern raised was not 
just over monarch butterflies, but on all other (non-target) species in the 
environment. (Bt-corn is transgenic corn expressing a protein, Bt, isolated 
from the soil bacterium Bacillus thuringiensis, which kills specific insect 
pests.) Unfortunately, amid the enormous publicity generated, the broader 
issue became reduced to the impact of Bt-corn on monarch butterflies. 

So, when the US Environment Protection Agency (EPA) issued a data call-in on 
December 1999 to consider re-registration of Bt corn, the Department of 
Agriculture’s Agricultural Research Service (USDA-ARS) responded by 
sponsoring a Monarch Research Workshop in Feb. 2000 to identify research 
priorities regarding Bt-corn and monarch butterflies. A request for proposals 
was announced in April, after which a steering committee selected projects to 
be funded from a grant pool provided by the USDA-ARS and the Agricultural 
Biotechnology Stewardship Technical Committee. 

The results of those projects were published in the 9 October 2001 issue of 
the Proceedings of the National Academy of Science USA, giving clearance to 
the EPA’s re-registration of Bt-corn for an additional seven years, announced 
16 October [1].

The first paper in the series is on risk assessment [2] based on data 
collected in all the studies. Here, we are immediately reassured by the 
statement, "This 2-year study suggests that the impact of Bt corn pollen from 
current commercial hybrids on monarch butterfly populations is negligible." 

On reading the fine print, one discovers that, 

"Toxicity of purified Bt proteins to larval stages of butterflies and moths 
is well known" from previous studies, and confirmed in the present ones. 
A transgenic corn expressing high levels of one of the Bt proteins, Cry1Ab, 
not only killed the butterfly larvae, but also inhibited growth with small 
numbers of pollen grains.But, these observations are not considered 
sufficient to cause concern, why not?

What matters in the first instance, we are told, is the probability of 
exposure, Pe, which is equal to three numbers I, o, and a, all less than one, 
multiplied together,

Pe = I o a

I is the proportion of monarchs that visit cornfields, o is the overlap of 
pollen-shed with susceptible larval stages and a, the adoption rate of Bt 

Furthermore, the actual risk R depends, not just on the probability of 
exposure, Pe, but also on Pt, the proportion of monarchs that would be 
exposed to pollen levels that exceed the lethal threshold, yet another number 
less than one.

R = Pe Pt

By such means, the risk becomes reduced to less than 1% or, better still, 
less than 0.1%. 

Should we be impressed with this kind of special pleading in the light of 
clear evidence that the Bt protein is harmful, and admitted to be so? 

The authors devoted several pages of unconvincing arguments in order to come 
up with estimates of the numbers, the only reliable one is perhaps the 
adoption rate, a, of Bt corn. All estimates are for the year under study, and 
could drastically change in future in any case. 

The studies on toxicity are on acute effects, ignoring both long-term 
cumulative and non-linear effects that are well known in the ecological 
literature, especially with regard to extinction and population density. 
These short-term studies on monarch butterflies do not address impacts on 
other non-target species, nor on the multiplier ecological consequences of 
all the impacts interacting with each other. 

Bt has already been shown to have the following additional negative impacts, 
as reviewed elsewhere by the two research teams who found clear evidence that 
Bt-corn pollen harmed the larvae of Monarch butterflies [3]: 

Increased mortality of lacewing larvae fed on artificial diet containing 
Bt-toxin or on corn-borer larvae that had eaten Bt-corn. 
Bt sprays used to reduce caterpillars in forests led to fewer black-throated 
blue warbler nests. 
A parasite of corn-borers, Macrocentris cingulum, was found to be reduced in 
Bt-cornfields compared with non-Bt corn fields. 
One preparation of Bt (var. tenebrionis), reported to be specific for 
Coleoptera, caused significant mortality in domestic bees. 
Soil-dwelling collembola, Folsomia candida, an important decomposer, suffered 
significant mortality from transgenic corn with Cry1 Ab. 
Bt not only remains in the soil with Bt-plant debris, it is actively exuded 
from the plant roots where it binds to soil particles and persists for 180 
days or more [4], so its effects on soil decomposers and other beneficial 
arthropods may be extensive. 
Bt-crops have speeded up the evolution of Bt-resistance in pest 
populations.In addition, Bt-toxins are actual and potential allergens for 
human beings. Field workers exposed to Bt spray experienced allergic skin 
sensitization and induction of IgE and IgG antibodies to the spray [5]. A Bt 
strain that caused severe human necrosis (tissue death) killed mice infected 
through the nose within 8 hours, from clinical toxic-shock syndrome [6]. Both 
Bt protein and Bt-potato harmed mice in feeding experiments [7].

Of course, proponents of Bt-crops can easily reduce all of those impacts, one 
at a time, to "negligible" levels by the same kind of exercise carried out in 
the ‘risk assessment’ described above; ignoring the complex interactions 
between the individual impacts which can have catastrophic long-term 

The proponents will still claim that the benefit of Bt-crops in reducing the 
use of broad-spectrum insecticides outweighs the risks. Unfortunately, that 
claim is not borne out by the evidence [3]. During the past five years, the 
percentage of field corn treated with insecticides in the US has remained at 
approximately 30%, despite a significant increase in the hectares of Bt corn 
planted. Corn borer is not a serious pest, and only 1% to 2% of the crops in 
Iowa was treated with insecticide for corn borer between 1995 and 1998. Most 
farmers in Iowa and Minnesota had never used insecticides for the corn borer. 
Only during years when corn borer densities are high do transgenic crops 
out-perform the non-transgenic. 

EPA press release Biotechnology Corn approved for Continued Use Oct.2001 <A HREF=""></A>
<A HREF="">b1ab9f485b098972852562e7004dc686/8db7a83e66e0f7d085256ae7005d6ec2</A> 
Sears MK, Hellmich RL, Stanley-Horn DE, Oberhauser KS, Pleasants JM, Mattila 
HR, Siegfried BD and Dively GP. Impact of Bt corn pollen on monarch butterfly 
populations: A risk assessment. PNAS 2001, 98, 11937-42. 
Obrycki JJ, Losey JE, Taylor OR and Jesse LCH. Transgenic insecticidal corn: 
beyond insecticidal toxicity to ecological complexity. BioScience 2001, 51, 
Saxena D and Stotzky G. Bt toxin uptake from soil by plants. Nature Biotech
.2001, 19, 199. 
Bernstein I, Bernstein J, Miller M, Tiewzieva S, Bernstein D, Lummus Z, 
Selgrade M, Doerfler D and Seligy V. Immune responses in farm workers after 
exposure to Bacillus thuringiensis pesticides. Environ Health Perspect 1999, 
Hernandez E, Ramisse F, Cruel T, le Vagueresse R and Cavallo JD. Bacillus 
thuringiensis serotype H34 isolated from human and insecticidal strains 
serotypes 3a3b and H14 can lead to death of immunocompetent mice after 
pulmonary infection. FEMS Immunol Med Microbiol 1999, 24,43-7 
Fares NH and El-Sayed AK. Fine structural changes in the ileum of mice fed on 
dendotoxin-treated potatotes and transgenic potatoes. Natural Toxins:1998: 6: 

This article can be found on the I-SIS website at <A HREF=""></A> The Institute of Science in Society 
<A HREF=""></A> 
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