Agricultural use of chemicals such
as pesticides and poisons poses extremely serious
threats to wildlife and people.
Farmers use a wide range of chemicals to protect
crops from insects and disease, to control ticks and
other parasites, and to kill predators such as jackal
and caracal. Government agencies use pesticides to
combat locusts, malaria-carrying mosquitoes, tsetse
flies and queleas.
Organochlorines: Of all the pesticides
ever used, the organochlorines have done the most
harm to wildlife. These include DDT, aldrin,
dieldrin, endrin,endosulphan and gamma-BHC. Besides
being toxic, organochlorines have various properties
which make them harmful to wildlife. For example,
they are extremely stable and remain unchanged in the
environment for many years. In addition, they are
stored and accumulate in the fat of animals, and thus
pass from prey to predator, concentrating at
successive steps in a food chain. Animals at the end
of food chains, such as birds of prey, are especially
likely to accumulate large amounts of poison.
As the side effects of organochlorines became
known in the 1960s, most nations placed restrictions
on their use. In South Africa and Namibia, DDT,
widely applied from 1946, was prohibited in
agriculture and is now used only by government for
malaria mosquito control. Manufacture of these
chemicals continues, however, and the main market has
shifted from developed to developing countries.
Zimbabwe, for example, imported 1000 tonnes of DDT in
Organophosphates: These have largely
replaced organochlorines in agricultural pest
control. They are thought to be safer than
organochlorines as they break down more rapidly.
Organophosphates are responsible for most acute
pesticide related poisonings amongst humans. In 1985,
organophosphate poisonings were the second most
common reason for Tygerberg Hospital's ICU
admissions. Carbamates and Pyrethroids:
These modern insecticides are usually not toxic to
mammals, but are extremely toxic to birds. Carbamates
are used in termite control and this can reasult in
the secondary poisoning of birds that have eaten
Pesticides play an important role in the control
of human and animal diseases, and crop pests.
However, the continued use of organochlorines, for
example, could seriously damage fish and wildlife
resources as well as pose a health hazard to man. The
challenge is to find ever safer and more specific
chemicals that have little or no effect on non-target
The use of poisons to kill `problem animals' such
as jackal, caracal, cheetah and leopard is causing
serious declines in scavenging animals. Farmers often
bait a carcass with a poison such as strychnine, and
leave it in the veld in the hope that a jackal or
caracal (the target species) will eat the meat and
die. However, scavenging birds such as vultures,
bateleurs and tawny eagles, all of which are very
good at finding carrion, come down to baited
carcasses and are poisoned. As the farmer never
intended this to happen, these animals are called
A number of scavenging raptors, e.g. Cape and
Egyptian vultures, and bateleur eagles, have been
driven to extinction over large areas as a result of
this practise. Other species have declined to
critically low numbers, e.g. lappetfaced and
whiteheaded vultures, tawny eagles. Also severely
affected have been non- target mammals such as the
aardwolf, aardvark, bat-eared and Cape fox, brown
hyaena and many smaller animals.
* In parts of Europe where the use of poisons is
banned for predator control, bird of prey numbers
have recovered well. It is high time that a similar
ban is introduced in all countries in southern
Africa. Although not banned, strychnine, one of the
most common, and most lethal poisons used to bait
carcasses, has to be prescribed by a veterinarian in
order for a farmer to obtain it.
* The Redbilled Quelea Working Group has been
formed to address the issue of controlling quelea (a
gregarious, seed-eating bird that can cause
tremendous crop losses). The application of Queletox
(active ingredient fenthion, an organophosphate) to
kill quelea, has resulted in widespread deaths of
non-target species such as birds of prey and herons.
* Arsenic is no longer used in stock dips.
DID YOU KNOW?
* It is estimated that for every target animal
poisoned, 100 - 300 non-target animals die.
* Although insectivorous, the aardwolf, aardvark,
bat-eared fox, and Cape fox are vulnerable to
poisoned carcasses as they are attracted to carrion
for the maggots they will find there.
* At levels too low to cause death,
organochlorines can disrupt the breeding of birds by
causing shell-thinning, egg-breakage, and death of
embryos in unbroken eggs. This results in population
decline and local extinction.
* The yellowbilled oxpecker, formerly widespread
in South Africa, had died out by 1910, mainly as a
result of the introduction of arsenical dipping for
livestock in 1902.
* Oxpeckers die within 48 hours after eating
arsenic coated ticks.
Study Group, Johannesburg, 1985.
Wildlife Trust and SA Ornithological Society,
FARMERS. A. Bowland, M. Mills and D. Lawson. Endangered Wildlife
Trust, Johannesburg, 1993.
POPULATION ECOLOGY OF
T. & A. Poyser. Calton, UK, 1979.
SCAVENGING RAPTORS ON FARMLANDS: WHAT IS
THEIR FUTURE? C Brown. African Wildlife
42(2): 103-105. 1988.
"SUPERJAKKALS" AND THE POISON
PEOPLE. J. Ledger. African Wildlife 40(3):
CARELESS HANDLING OF PESTICIDES STILL
CAUSES POISONING INCIDENTS. J. Ledger.
African Wildlife 40(3): 91, 1986.
POISONING BY CHEMICALS IN AGRICULTURE AND
PUBLIC HEALTH: TRADE NAMES, CHEMISTRY,
CLASSIFICATION, TOXICOLOGY, SYMPTOMOLOGY AND
TREATMENT PROCEDURES. H. Fourie. ENG
Enterprises, Pretoria, 1984.
Endangered Wildlife Trust. Private Bag X11,
Parkview 2122. Tel. 011-4861102.
Poison Working Group. PO Box
15121, Lynne East, 0039. Tel. 012-808 0592.
Vulture Study Group. PO Box
72334, Parkview, 2122. Tel. 011-646 8617.
Animal Rehabilitation Centre. PO
Box 15121, Lynne East, Pretoria, 0039. Tel. 012-808
1106. Treat and care for poisoned animals.
AVCASA. Agricultural and Veterinary
Chemicals Association of South Africa. PO
Box 1995, Midrand, 1685. Tel. 011-805 2000.
Provincial conservation authorities. See telephone
book for details.
Poison Information Centre. For
advise on cases of human poisoning: Johannesburg
011-642 2417, Bloemfontein 051-475 353, Cape Town