GMO Myths and Truths

3.6 Myth: GM Bt insecticidal crops only harm insects and are
harmless to animals and people
Truth: 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EU, now withdrawn) and natural Bt toxin. 11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 BSEinfected
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
GMO Myths and Truths 51