Organochlorine Insecticide Residues in African Fauna: 1971–1995

Abstract

Organochlorine insecticides (OCLs), which were introduced in the decade following World War II, were used extensively in Europe, the U.S., and other developed countries into the 1970s. However, data began to accumulate on their persistence in soils and aquatic sediments, their potential to be taken up into animal tissues and to bioconcentrate in birds and mammals in the higher tropic levels of food chains and even in humans. As a result, registration authorities phased out their use progressively, in Europe and the U.S., from 1973 onward. However, the production of OCLs in developed countries and their use in developing countries continued through the 1970s and 1980s into the 1990s because they were, no longer under patent agreement, were inexpensive to manufacture, and were very effective in pest control. In Africa, the use of OCLs continued well into the 1990s for the control of mosquitoes, tsetse flies, and desert locusts as well as to combat various crop, animal, and human pests. Some of these uses involved extensive spraying of large areas of nonagricultural land, thereby exposing many groups and species of wildlife to their residues. Although there is some evidence of a gradual decline in the use of OCLs in Africa, they are still being used in appreciable quantities. During the past 25 yr, there have been 50 published reports of OCL residues in the various groups of invertebrate and vertebrate animals constituting the African fauna. These have been based on a diverse range of surveys, target animals, sampling methods, and analytical techniques. Moreover, they are extremely regionally-biased, the most intense surveys being in Zimbabwe, Kenya, Egypt, and South Africa. DDT was the most commonly used OCL, accounting for about half the total use, followed closely by dieldrin and HCH. Birds and fish have been sampled most intensively, with relatively few studies on other taxa. We reviewed the OCL residue data on African fauna from these reports and summarized the maximum and mean residues in the various groups of terrestrial and aquatic invertebrates and vertebrates. Overall, residues in the fauna were the greatest for DDT, followed in turn by those of dieldrin, HCH, endosulfan, and endrin, with small amounts of aldrin and toxaphene being found in some animals. There were relatively few reports of OCL residues in terrestrial invertebrates and virtually none in aquatic invertebrates. Only a few reports demonstrated OCL residues in terrestrial vertebrates, although high levels of DDT, dieldrin, and HCH were found in crocodile eggs and large residues of dieldrin occurred in bats, squirrels, and monkeys. Considerable OCL residues were reported in a few species of fish, especially Barbus, Clarias, Hydrocynus, Labeo, Sarotherodon, Epiplatys, and Synodontis. These residues were at levels that could have caused chronic toxicity or behavioral changes. The calculated maximum and mean OCL residues in the various elements of the African fauna until 1995 were compared with those calculated for corresponding faunal groups in Europe and the U.S. from their development and introduction up to 1973. The OCL residues reported in African fauna between 1971 and 1975 tended to be significantly higher overall than those published for Europe and the U.S. In particular, residues of DDT and dieldrin in African birds and their eggs were greater than those that had been incriminated as causing significant eggshell thinning and reproductive failure in European and U.S. aquatic and terrestrial birds up to 1973. Additionally, high DDT and dieldrin residues were reported from some species of African fish at levels that could potentially affect their reproduction, have chronic toxic and behavioral effects, and even drastically affect populations. Holistic case studies on the use of OCLs to control tsetse flies and desert locusts were discussed. OCL levels in trophic levels of fauna associated with Lake Kariba (between Zambia and Zimbabwe) were summarized. (AB