PESTS OR PESTICIDES?
Dr. JOE SCHWARCZ
is Director of McGill University’s Office for Science
and Society. He hosts The Dr. Joe Show on Montreal's CJAD and
has appeared hundreds of times on The Discovery Channel, CTV,
CBC, TV Ontario and Global Television. Dr. Schwarcz also writes
a newspaper column entitled The Right Chemistry and
has authored four best sellers, Radar, Hula Hoops and
Playful Pigs, The Genie in the Bottle, That's the
Way the Cookie Crumbles, and Dr. Joe and What You Didn’t
are nasty chemicals. They have to be. You don’t beat off
the myriad insects, weeds and fungi which look upon our food
supply as their food supply with sweet smells and pleasant tastes.
You do it by poisoning them. Hopefully, without poisoning ourselves.
were born out of necessity. The cultivation of crops has always
been characterized by a relentless battle against pests, a battle
which required farmers to take up chemical arms. Thousands of
years ago the Sumerians learned to dust crops with elemental
sulphur and the ancient Romans drove insects from their orchards
by burning coal tar. The discovery of the toxicity of lead and
arsenic compounds led to the extensive use of lead arsenate
in agriculture, without much concern for its effects on human
health. After all, producing enough food to feed the growing
population was the prime goal.
pyrethrum and rotenone extracted respectively from tobacco,
chrysanthemum and derris plants joined the chemical stockpile
by the 19th century. Malathion and chlorpyrifos, typical organophosphates,
were born out of research into poison gases during WW II, and
the rapid advances in chemistry in the post-war era introduced
synthetic pesticides such as DDT, benzene hexachloride and dieldrin.
Insects shuddered, fungi floundered, weeds wilted and agricultural
yields boomed. And at least in the developed world, worries
about lack of food began to be replaced by concerns about pesticides.
Rachel Carson’s Silent Spring alerted us to the
possible effects of pesticides on biodiversity, and we heard
the faint rumblings of epidemiological studies linking occupational
pesticide exposure to health problems.
chemists, armed with their gas chromatographs and mass spectrometers,
heightened our fears by revealing that it was not only farmers
or agro-chemical producers who were exposed to pesticides, we
all were! Residues of these chemicals were found on virtually
everything we ate. Apples, for one, were tainted with Alar,
a plant growth regulator sprayed on trees to prevent the fruit
from falling prematurely. This chemical had cruised under the
public radar until 1989 when the popular TV program 60 Minutes
lowered the boom by introducing a segment on Alar with a picture
of an apple bedecked with the classic skull and crossbones as
a reporter enlightened us about the “fact” that
“the most potent cancer-causing agent in our food supply
is a substance sprayed on apples.” People responded by
flushing apple juice down the drain and removing apples from
children’s lunch boxes. But the fact is that the “fact”
that Alar was the most potent carcinogen in our food supply
was not a fact. True, one of the breakdown products of Alar,
1,1-dimethylhydrazine, did induce tumours when fed to mice in
huge doses, an effect that regulators were well aware of when
approving Alar for commercial use. The carcinogenicity study
was questionable, they maintained, and irrelevant as a model
for human exposure.
or not Alar ever posed a risk is still debated, but there is
no doubt that it placed the issue of pesticide residues in food
on the front burner. Toxicologists, agronomists, physicians
and environmentalists all waded in with their opinions, along
with hordes of emotionally-charged consumers who were clearly
out of their depth in such a complex discussion. Bruce Ames
of the University of California, one of the most respected biochemists
in the world, was quick to point out that we are exposed to
all sorts of toxins, both synthetic and natural, on a continuous
basis and that more than 99.9% by weight of pesticides in the
average diet are naturally occurring compounds that plants produce
to defend themselves against insects and fungi. Potatoes, for
example, synthesize solanine and chaconine, compounds which
like some synthetic pesticides inhibit the activity of cholinesterase,
a crucial enzyme. But we don’t shun potatoes because they
harbour these natural pesticides. According to Ames and other
experts, the body doesn’t handle natural pesticides differently
from synthetic ones, so there seems to be little justification
for all the hand-wringing over remnants of synthetic pesticides
in our food supply, usually measured in parts per trillion.
Take a football field, pile it with sand to a height of some
eighteen feet, mix in one single grain of red sand, and search
for it. You’ll be searching for 1 ppt!
course, some will argue that there is nothing we can do about
the natural toxins, and their presence does not justify a cavalier
use of synthetic pesticides. True, but our use of pesticides
is anything but cavalier. Regulatory agencies demand rigorous
studies before a pesticide is approved. This involves determining
the maximum dose that causes no effect in a test animal and
dividing it by a safety factor of at least 100 for human exposure.
Furthermore, when the risk of pesticide residues is assessed,
the supposition is that the food contains 100% of all legal
residues and that people eat these foods for seventy years.
That sounds comforting, especially when we learn that more than
70% of fruits and vegetables have no detectable pesticide residues
and only about 1% of the time is the legal limit exceeded, a
limit that already has a hundred-fold safety factor built-in.
Of course, produce should still be washed, although more for
removal of bacteria than pesticides. A 30 second rinse significantly
reduces both water soluble and insoluble pesticides.
debates about the validity of using animal models to determine
human carcinogenicity, about whether or not there is a threshold
effect for carcinogens, and about the possibility of trace residues
of pesticides which may be harmless individually but not when
they team up, will continue. So will the use of pesticides.
By the year 2030, ten billion people will be coming to dinner.
But without the sensible use of pesticides they will be going
home hungry. Would a pesticide-free world be better? For people
who have to handle pesticides occupationally, and for the environment,
yes. For the consumer, no. Yields would be significantly reduced,
and in light of the overwhelming evidence of the ability of
fruits and vegetables to protect against cancer, public health
would be compromised.