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BY DR GIO BRAIDOTTI
T he staple food for up to a billion people
in the tropics has a major health
drawback: cassava's edible tubers and
leaves contain a potent poison---compounds
However, the Australian plant chemist
Dr J. Howard Bradbury explains that there is a
survival advantage to the plant from making
these compounds---they repel predators,
allowing the plant to thrive in the tropics.
Remove the poison, as some US bioscientists did,
and the plant becomes weak and ineffective.
The plant is popular, especially in tropical
Africa, because it yields well in any conditions
and is drought resistant. Its cultivation is
spreading, but problems occur when it spreads
faster than the food-processing know-how
needed to prevent cyanide poisoning.
"Frequent consumption of insufficiently
processed bitter roots and flour causes paralysis
of the legs," Dr Bradbury says. "This disease is
called konzo and affects mainly rural children
and women of child-bearing age in Africa, with
Angola recently becoming the sixth African
country affected by konzo."
In the 1980s Dr Bradbury was funded by
ACIAR to analyse the tropical root crops of
the South Pacific region and he realised then
that the cyanogens present in cassava could
be a health problem in Africa. Upon retiring
from the Australian National University (ANU),
he became a visiting fellow and opted to do
something about his concerns.
With ACIAR support, at ANU he developed a
cyanide-detection kit that requires no advanced
laboratory equipment or expertise. The kit
provides a colour-coded measure of cyanide
levels in cassava roots and flour. It was first made
available worldwide in 1996 and can be used by
anyone with a high-school level education.
Since then Dr Bradbury has been
manufacturing the kits at ANU. Each kit
contains enough material to run 100 tests
and he gives away about two kits for each
one he sells (at a current price of $450) and
uses the money to develop other konzo-
The kit has proven especially popular with
plant breeders working in remote locations.
It allows them to select for high-performing
but low-cyanide cassava varieties---a selection
CASSAVA, CYANIDE AND KONZO DISEASE
A disability caused by a staple food, which leaves people unable or struggling to walk, is
potentially devastating to a poor rural community. A sample test kit is helping to reduce
this disability throughout the developing world.
strategy that is known to reduce the risk of
Dr Bradbury's kits have been used in this
capacity in East Timor since 2006 by the
AusAID-funded ACIAR Seeds of Life project, as
part of cassava-improvement efforts.
"The kits are made at ANU but are sent out
all over the world, including the US, the UK and
Latin America where the Amazonian cassava
plant originated," he says.
In total, about 750 kits have been distributed
in the past 15 years, often to researchers in
universities and agricultural institutes. To ensure
the technology is available to all who need it,
Dr Bradbury has avoided patenting his
invention and has published instructions on
how to make the kits.
He has also developed the 'wetting method'
to lower cyanide levels in cassava flour by up to
In the wetting method, dry flour is placed in
a bowl and the level it reaches is marked in the
inside of the bowl. Water is added with stirring
until the wet flour reaches the mark. The wet
flour is then placed in a thin layer on a basket
and left in the shade for five hours or in the
sun for two hours to allow hydrogen cyanide
gas to escape. The damp flour is cooked in
boiling water in the traditional way to make a
"Developing the wetting method was one
of the most practical things I've ever done as
a chemist," he says. "It is currently undergoing
testing in Africa in a particularly badly affected
village in the Democratic Republic of Congo."
Urine checks---which use a kit developed by
Dr Bradbury to measure thiocyanate levels---
indicate that the proportion of children in
danger of getting konzo has dropped from
49% to 28% since the adoption of the wetting
method by women.
Despite these efforts, Dr Bradbury has no
illusions about the underlying cause of konzo.
"When people get konzo, cassava makes
up 80% or more of their food intake. If diet
were improved they would never get konzo.
A shortage of proteins---especially protein
that provides the sulfur-containing amino
acids needed by the body to clear cyanide---is
making people more susceptible." n
Dr J. Howard Bradbury at the ANU glasshouse
surrounded by cassava plants and holding up the
colour chart from the cyanide detection kit he
developed to help prevent konzo disease. The ten
shades in the chart represent from zero up to 800 parts
per million cyanide.
In Mozambique, these twin four-year-old boys can no
longer walk as a result of konzo.
PHOTOS: J HOWARD BRADBURY
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