Are crops that produce the Bt protein dangerous for people?

Bt crops are genetically modified to create a crystal protein from the Baccillus thurigensis bacterium, which, when ingested by insects feeding on the crops, kills the insect pests. The Bt toxin, one common one is called CRY1A, pokes microholes in the gut of the insect, and the insect dies. Bt spores do not spread to other plants or insects on their own and Bt powder spread on plants is easily washed off and becomes ineffective.

Created in 1995, potatoes which create Bt crystal proteins were approved for crops in the US. In 1996 corn was approved for growth in the US. By 2014, 7 million farmers were using Bt cotton in India.

Bt powder is a preferred method of insect control for backyard farmers as it can be washed off easily before the food is eaten, but when the cry protein is in the plant itself, it cannot be washed off, and is consumed by people.

Bt action is very specific. Different strains of Bt are specific to different receptors in insect gut wall. Bt toxicity depends on recognizing receptors, damage to the gut by the toxin occurs upon binding to a receptor. Each insect species possesses different types of receptors that will match only certain toxin proteins, like a lock to a key. It is because of this that farmers have to be careful to match the target pest species with a particular Bt toxin protein which is specific for that insect. This also helps the beneficial insects because they will usually not be harmed by that particular strain of Bt.

The EPA has found Bt to be safe yet we already know the track record of the EPA: it's in the pocket of big biotech and conveniently ignores facts that will affect biotech profits. In the 1990s the EPA was also the agency which declared meltwater ditches next to roads on private property a "protected watershed" (even though the water was temporary) and even quarantined property from homeowners and prevented from doing something as simple as planting flowers too close to the "watershed". (When a property was declared a "watershed" it became protected. So even though the owner paid money for the property, they were unable to develop it for commercial or residential purposes.) Past performance is the best indicator of future performance. 

Bt pellets work well in controlling mosquito larva in ponds, but it appears to kill all other invertebrates, in my experience. The good part is the Bt does not survive the winter in my pond. (The next spring I added back ostracods and daphnia and they survived.)

In 2011 a study found that Bt toxins (cry proteins) killed fetal cells inside human mothers.

In 2013, scientists found the Bt cry toxin (aka cry protein) CRY1AB was affecting blood cells in mice. Their conclusion was that cry proteins cause some problems in vertebrates and the toxic effects increase with long-term exposure.

In the cast of GMO crops that produce the Bt toxin, it may be better to avoid them altogether. Better safe than sorry. See also "The Failure of the Scientific Establishment" which lists more items mainstream science claimed was safe.

Links

1. Arisa, Aziz and Samuel Leblancc (University of Sherbrooke). Maternal and fetal exposure to pesticides associated to genetically modified foods in Eastern Townships of Quebec, Canada. Reproductive Toxicology. May 2011. Link to Elsevier abstract.
2. Bt info from UCSD.
3. EPA Biopesticide fact sheet. 
4. Mezzomo BP, Miranda-Vilela AL, Freire IdS, Barbosa LCP, Portilho FA, et al. (2013). Hematotoxicity of Bacillus thuringiensis as Spore-crystal Strains Cry1Aa, Cry1Ab, Cry1Ac or Cry2Aa in Swiss Albino Mice. J Hematol Thromb Dis. 1: 104. doi:10.4172/jhtd.1000104. Link to PDF. 
5. Wikipedia.