GM Bt insecticidal crops only harm insects and are harmless to animals and people
GM Bt insecticidal crops pose hazards to people and animals that eat them
Many GM crops are engineered to produce Bt toxin, a type of insecticide. Bt toxin in its natural, non-GM form is derived from a common soil bacterium and is used as an insecticidal spray in chemically-based and organic farming.
Regulators have approved GM Bt crops on the assumption that the GM Bt toxin is the same as the natural Bt toxin, which they say has a history of safe use. They conclude that GM crops engineered to contain Bt insecticidal protein must also be harmless.
But this is false, for the following reasons:
- Natural Bt toxin is not necessarily the same as the Bt toxin expressed by GM Bt plants. The Bt toxin protein in GM plants may be truncated or otherwise modified. For example, there is at least a 40% difference between the toxin in Bt176 maize (formerly commercialised in the EU, now withdrawn) and natural Bt toxin.11 Such changes can mean that they have very different effects on people or animals that eat them. Prions (the folded proteins found in BSE-infected cows), venoms, and hormones, are all proteins, but are far from harmless.83
- The natural Bt toxin used in insecticidal sprays behaves differently in the environment from the Bt toxin produced in GM plants. Natural Bt breaks down rapidly in daylight and only becomes active (and toxic) in the gut of the insect that eats it. It does not persist in the environment and so is unlikely to find its way into animals or people that eat the crop. With GM Bt crops, however, the plant is engineered to express the Bt toxin protein in active form in every cell. In other words, the plant itself becomes a pesticide, and people and animals that eat the plant are eating a pesticide.
- Even natural Bt toxin has been found to have negative health effects. In farm workers, exposure to Bt sprays was found to lead to allergic skin sensitisation and immune responses.84 And laboratory studies found that natural Bt toxin has ill effects on mammals, producing a potent immune response and enhancing the immune response to other substances.85,86,87
- Safety tests for regulatory purposes are generally not carried out on the Bt toxin protein as expressed in the GM plant. The Bt toxin protein that is tested is usually derived from genetically engineered E. coli bacteria, as GM companies find it too difficult and expensive to extract enough Bt toxin from the GM crop itself. As we have seen, the GM process gives rise to unexpected changes in the desired protein, so it cannot be assumed that the Bt toxin protein derived from E. coli bacteria is the same as the protein derived from the GM plant that people and animals will eat. Indeed, the US Environmental Protection Agency, in its review of the commercialised Monsanto GM maize MON810, said it produces a “truncated” version of the protein – in other words, a protein that is not the same as the natural form.60 Such changes can make a protein more toxic or allergenic.
3.6.1. Bt toxin does not only affect insect pests
GM proponents claim that the Bt toxin engineered into GM Bt crops only affects the target pests and is harmless to mammals, including people or animals that eat the crops.88 Based on this assumption, regulators do not require human toxicity studies on GM Bt crops.
But the assumption is incorrect. In a 2012 test-tube (in vitro) study, genetically engineered Bt toxins were found to be toxic to human cells. One type of Bt toxin killed human cells at the dose of 100 parts per million. The findings showed that GM Bt toxin does affect humans, contrary to claims from the GM lobby and regulators.83
The GM lobby responded by saying that in vitro studies do not accurately reflect what happens in a living human or animal that eats GM Bt crops. But other independent studies have found that GM Bt crops have adverse effects when fed to laboratory animals. Findings include:
- Toxic effects on the small intestine, liver, kidney, spleen, and pancreas12,14,16,21,40
- Disturbances in the functioning of the digestive system16
- Reduced weight gain12
- Immune system disturbances.15
Aside from laboratory animals and human cells, GM Bt crops have been found to have toxic effects on butterflies and other non-target insects,89,90,91 beneficial pest predators,92,93 bees,94 and aquatic95,96 and soil organisms97 (see section 4).
It is premature to say that the toxic effects associated with GM Bt crops are due to the Bt toxin from the crops. The effects may be due to one or more of the following causes:
- The Bt toxin as produced in the GM crop
- New toxins produced in the Bt crop by the GM process, and/or
- Residues of herbicides or chemical insecticides used on the Bt crop. Many Bt crops have added herbicide-tolerant traits,98 making it likely that herbicide residues will be found on them.
3.6.2. Bt toxin protein may not be broken down harmlessly in the digestive tract
GM proponents claim that the Bt toxin insecticidal protein in GM plants is broken down in the digestive tract and so cannot get into the blood or body tissues to cause toxic effects.
But digestion is generally an incomplete process and studies show that Bt toxin protein is not always fully broken down:
- A study on cows found that Bt toxins from GM maize MON810 were not completely broken down in the digestive tract.99
- A study simulating human digestion found that the Bt toxin protein was highly resistant to being broken down in realistic stomach acidity conditions and still produced an immune response.100
- A study conducted on pregnant and non-pregnant women in Canada found Bt toxin protein circulating in the blood of pregnant women and the blood supply to their foetuses, as well as in the blood of non-pregnant women.65 Questions have been raised about the validity of the detection method, but further investigation is needed before Bt crops can be claimed to be safe for humans.
Studies on GM Bt crops show that Bt toxin is not specific to a narrow range of insect pests but can affect a wide variety of non-target organisms. Taken together, the studies on GM Bt crops and natural Bt toxin raise the possibility that eating GM crops containing Bt toxin may cause toxic or allergic reactions and/or sensitise people to other food substances.