A number of highly persistent
organochlorine (OC) pesticides, widely banned in other countries, are still used
in African countries, including DDT, lindane, heptachlor, chlordane and
toxaphene. Endosulfan, a less persistent OC, is also widely used. The lower cost
of these older pesticides means farmers in poorer areas find them attractive and
affordable. The dangers resulting from their accumulation through food chains,
interference with reproduction of mammals and birds, and toxicity to aquatic
life, are little known among farmers.
Most data on the environmental impact of pesticides are based
on studies in temperate climates. African countries have less information than
other tropical regions because the pesticide market is smaller and the
infrastructure poor. A Swedish-funded study initiated in the 1980s set out to
redress the problem and supported studies in Algeria, Egypt, Ghana, Nigeria,
Tanzania, Uganda, Zambia and Zimbabwe. The programme, which was coordinated
through the International Atomic Energy Agency (IAEA) joint division with the
Food and Agriculture Organisation (FAO) in Austria, also helped build skills and
standardised experimental procedures in participating countries, increasing the
capacity for residue analysis and developing validated methods for
ecotoxicological studies.
The studies focused on maize production systems and the major
maize pest, stem borer, but other crops were included. It investigated the
effect of OCs on beneficial insects and the agroecosystem, environmental
persistence, and the effects on higher fauna. The exercise presented the
multi-disciplinary teams with numerous practical challenges as they combated
drought, electricity failures, and in one case a closure of the University
system, but it contributed significantly to knowledge of pesticide impacts in
Africa and provided useful comparative material.
Looking at environmental persistence, results confirmed that
lindane and endosulfan persist for a shorter period in areas of high temperature
and heavy rainfall. Most studies showed that lindane reduced the incidence of
pest attack on maize although there was not always a corresponding increase in
crop yield. On the other hand lindane was not recommended for use on maize in
some of the countries studied. The population of non-target organisms and
beneficial insects were reduced, but in most cases recovered within 6-8 weeks
and the adverse impact did not appear to last from one season to the next. Of
concern also were findings of OC residues in fish which were of higher
concentration than in the water, and a scarcity of fish in rivers which
suggested a toxic agent was present. Surveyed birds in Tanzania, notably African
Fish Eagles from Lake Victoria, showed residues of DDT and the Egyptian study
showed degenerative changes in liver, kidney and nerve tissue of birds sampled.
While the studies provide useful scientific knowledge and
testing protocols, they also raise questions. Some comparisons showed no impact
on economic return from use of the OC compounds. Others which showed higher
yields from sprayed crops compared to unsprayed crops did not provide any data
on whether the unsprayed crops were simply left, or whether a more benign pest
management regime was used. The research on environmental persistence did not
examine evidence that OCs move from tropical to temperate regions on water and
air currents, where they are now accumulating. We can also assume that under
experimental conditions, recommended doses of the OCs were used with well
maintained equipment, a situation which does not equate with field conditions. (BD)
Organochlorine insecticides in African
Ecosystems, Report on a Final Research Co-ordination Meeting, Food and
Agriculture Organisation/International Atomic Energy Agency, Wagramerstasse 5,
PO Box 100, A-1400 Vienna, Austria, March 1997, 250pp.
[This
article first appeared in Pesticides News No. 36,
June 1997, page 6]