A study has been published which blows all assumptions about the safety of 'Bt' insecticidal GM proteins out of the water.
Biotech industry genetic engineers have been getting great mileage out of proteins modelled on those produced by the soil bacterium Bacillus thuringiensis ('Bt'). These transgenic look-alikes come in an infinite variety and can be designed to target specific pests.
Bt proteins' assumed safety is based on their long history of safe use as cultured spore suspensions in foliar sprays. It's taken for granted that their protein chemistry means they will be denatured during digestion, and that their need for activation by specific gut conditions and cell-surface receptors found only in insects will make other animals (including humans) immune to their toxic effects.
All the above assumptions are over-generalisations: transgenic Bt is different in structure and origin from the familiar, natural forms, plus, as the authors of the study note, “little is known about (Bt proteins') toxicological potential”. Our traditional exposure has been to live bacteria on our skin and in our lungs, not to large quantities of a single, concentrated protein sequestered and possibly stabilised inside food material. Assumptions of digestibility and insect specificity are theories which were not checked by science prior to the commercialisation of Bt-generating GM crops.
Experiments have already shown that Bt proteins (natural or artificial) kill by bursting cells. If conditions are carefully adjusted, Bt can burst red blood cells from rats, mice, sheep, horse and humans. Because blood cells are generated constantly and their production can rapidly be stepped up in response to adverse events such as a toxin entering the body, changes in quality, quantity and maturity are quickly apparent.
In the study, mice were fed a single 'meal' of four transgenic Bt toxins in the form of GM bacterial spores. The various Bt proteins were fed both individually and in combination. Blood cell analyses were carried out after one, three and seven days.
The changes observed indicated toxic effects on the bone marrow tissue which generates blood cells. Red cells were particularly targetted, and three of the Bt-toxins induced a highly inflammatory response in the white blood cells. What was observed wasn't a simple reaction to all Bt proteins, because the dose- and time-responses were different for each one.
Toxic signs were evident even at the lowest dose of one of the Bt analogues ('cry1Ab') which is widely incorporated into commercial GM crops: it has also been found circulating in pregnant and non-pregnant women and foetuses in Canada 
The authors concluded that the four Bt toxins tested “can cause some hematological risks to vertebrates, increasing their toxic effects with long-term exposure. Taking into account the increased risk of human and animal exposures to significant levels of these toxins, especially through diet, our results suggest that further studies are required to clarify the mechanism involved ... before concluding that these microbiological control agents are safe for mammals.” 'Mammals' includes, of course, humans.
The ‘mechanism’ needing 'clarified' includes:
- how a protein assumed to be digested is, nevertheless, ending up in the body of the consumer
- how a toxin assumed to be activated only in conditions found in an insect gut is, nevertheless, inducing changes in mouse blood and inside mouse bones.
- how a toxin assumed to require an insect molecular receptor on an insect gut cell and insect gut conditions is, nevertheless, harmful to mouse blood cells.
- how the Bt proteins tested are not only unexpectedly toxic, but clearly act and interact in different ways.
Transgenic Bt made by plants isn't, of course, the same thing as transgenic Bt made by bacteria: the plant version could be much more damaging.
This paper sounds a very tangible warning about possible harmful effects from many GM crops available now or in the pipeline. Given the GM-lobby habit of shooting-the-messenger, for example Arpad Pusztai after giving his warning about GM potatoes which weren't even on the market , and Gilles-Eric Séralini since he gave his warning about Roundup herbicide and at least one Roundup Ready maize which accumulates it , how come this latest damning science has slipped through the net? Perhaps it's just a matter of time.
 Trials conducted for the UK Government in Scotland in 1998 found that rats fed insecticide-
generating GM potatoes developed immune reactions in their gut wall. The scientist, Dr. Arpad Pusztai, was suspended, gagged and eventually dismissed. The Lancet recommended that Pusztai's study be repeated: this has not been done.
 GM MAIZE IS NOT SAFE TO EAT - News, October 2012
 GM PESTICIDES INSIDE YOU - News, April 2011
- Bélin Poleto Mezzomo et al.(2013) Hematoxicity of Bacillus thruringiensis as Spore-crystal Strains Cry1Aa, Cry1Ab, Cry1Ac or Cry2 Aa in Swiss Albino Mice, Journal of Hematology & Thromboembolic Diseases 1:1
- Bt toxins are toxic to the blood of mice, GM Watch 2.05.13