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Organic not always greener choice: study

June 24, 2010, Guelph, Ont – Consumers shouldn’t assume that, because a product is organic, it’s also
environmentally friendly

June 24, 2010, Guelph, Ont
– Consumers shouldn’t assume that, because a product is organic, it’s also
environmentally friendly.

A new University of Guelph
study reveals some organic pesticides can have a higher environmental impact
than conventional pesticides because the organic product may require larger
doses.

Environmental sciences
professor Rebecca Hallett and PhD candidate Christine Bahlai compared the
effectiveness and environmental impact of organic pesticides to those of
conventional and novel reduced-risk synthetic products on soybean crops.

“The consumer demand for
organic products is increasing partly because of a concern for the
environment,” said Hallett. “But it’s too simplistic to say that because it’s
organic it’s better for the environment. Organic growers are permitted to use
pesticides that are of natural origin and in some cases these organic
pesticides can have higher environmental impacts than synthetic pesticides
often because they have to be used in large doses.”

The study, which is
published in the journal PLoS ONE, involved testing six pesticides and
comparing their environmental impact and effectiveness in killing soybean
aphids – the main pest of soybean crops across North America.

The two scientists
examined four synthetic pesticides: two conventional products commonly used by
soybean farmers and two new, reduced-risk pesticides. They also examined a
mineral oil-based organic pesticide that smothers aphids and another product
containing a fungus that infects and kills insects.

The researchers used the
environmental impact quotient, a database indicating impact of active
ingredients based on such factors as leaching rate into soil, runoff, toxicity
from skin exposure, consumer risk, toxicity to birds and fish, and duration of
the chemical in the soil and on the plant.

They also conducted field
tests on how well each pesticide targeted aphids while leaving their predators
– ladybugs and flower bugs – unharmed.

“We found the mineral oil organic
pesticide had the most impact on the environment because it works by smothering
the aphids and therefore requires large amounts to be applied to the plants,”
said Hallett.

Compared to the synthetic
pesticides, the mineral oil-based and fungal products were less effective, as
they also killed ladybugs and flower bugs, which are important regulators of
aphid population and growth.

These predator insects
reduce environmental impact because they naturally protect the crop, reducing
the amount of pesticides that are needed, she added.

“Ultimately, the organic
products were much less effective than the novel and conventional pesticides at
killing the aphids and they have a potentially higher environmental impact,”
she said. “In terms of making pest management decisions and trying to do what
is best for the environment, it’s important to look at every compound and make
a selection based on the environmental impact quotient rather than if it's
simply natural or synthetic. It’s a simplification that just doesn’t work when
it comes to minimizing environmental impact.”