Bt: Miracle Organic Pesticide
or Potential Environmental Disaster?
Bt, or Bacillus thuringiensis,
has been used in some form or another for almost half a century as a specific
pesticide against various insects. For some years, it has been one of the
most effective pesticides organic growers can use. Bt is a natural organism
found at low levels in soils throughout the world. It works by secreting
one or more toxins after being ingested by an insect. The toxins are often
specific to a family of insects. It appears not to harm humans or other
life forms except for the intended targets.
It’s natural, it’s selective.
So, what’s the problem?
Increasingly, the types of Bt
being used are rare strains that are performance-enhanced or sometimes
genetically engineered. The use of Bt pesticides has spread from farms
and occasional homeowner use to the spraying of millions of acres every
year around the world, often over large tracts of forest land or areas
with large urban populations.
The Bt strains being used are
applied at rates up to one billion times the natural levels. Often, they
wipe out entire families of insects in the sprayed areas. For instance,
Btk, a strain used to control moth pests such as tussock and gypsy moth,
kills all insects in the Lepidoptera family (moths and butterflies). Soil
biota is also affected – there is evidence to show that nematodes and predator
insects (that would naturally control the pest population) are depressed
Despite Bt’s purported safety
for humans, no long term testing has ever been done to assure its safety.
Why should you worry?
Bt is extremely similar (so
much so it is difficult to distinguish without sophisticated testing) to
two other bacteria, B. cereus, which causes food poisoning, and B. anthracis,
which causes anthrax.
Bt secretes many of the
same toxins B. cereus does when it is growing. There is mounting evidence
that spores germinate in humans and can live for extended periods of time
in the respiratory and gastrointestinal tract. The effect of these low
level infections is unknown, but there have been isolated reports of disease
caused by Bt. One of the reasons Bt may not be seen as a common cause of
sickness is that it is very hard to test for its presence – many cases
diagnosed as B. cereus gastroenteritis (a fairly common form of food poisoning)
may in fact be caused by Bt.
People with sensitive immune
systems could be affected in ways we do not yet know, but immune responses
are seen when Bt infections establish in humans.
DDT was used for thirty years
and was claimed to be extremely safe for humans. The same sort of testing
done to arrive at that conclusion has been done with Bt.
Like it or not, we are all part
of a big experiment now, as the world’s agricultural and timber industries
increasingly rely on applications of different Bt strains to more and more
land and estuarine areas. Attempts to moderate the amount of spraying by
activist groups throughout the world are met with the unified opposition
of drug and pesticide companies and agribusiness.
Unfortunately, when Bt pesticides
are formulated, a number of “inert” ingredients are added as preservatives,
enhancers, and flow and wetting agents. These inerts are never revealed
by manufacturers or tested for safety, and some may be toxic. For instance,
Foray 48B, a common moth insecticide, probably contains the chemical BIT
(1,2-benzisothiazolin-3-one) that was recently prohibited for environmental
releases in the EU.
In the US alone, well in
excess of one million acres per year are treated with Btk and Bti pesticides
to control gypsy moth, tussock moth, and mosquitoes. Often these applications
are in cities or suburban areas. Aerial and ground applications supply
more Bt spores in a single breath to inhabitants than they would get by
eating a year’s worth of unwashed organic produce. Bt spores infiltrate
effectively into closed homes and remain at high concentrations in the
air for days after a single spraying.
The wholesale use of Bt pesticides
and Bt toxin GM crops (a whole other topic) will also endanger Bt’s use
in organic farming, because insects may eventually develop resistance to
the natural Bt toxins. This will force growers to use genetically modified
and untested (and more expensive) Bt’s.
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