Chlorinated hydrocarbon pesticide residues in eggs of some birds in Zimbabwe

Environmental Pollution (Series B) 5 (1983) 147-155

Chlorinated Hydrocarbon Pesticide Residues in Eggs of Some Birds in Zimbabwe J. Tannock* Chemistry and Soil Research Institute, Department of Research and Specialist Services, PO Box 8100, Causeway, Zimbabwe

W. W. Howellst Department of National Parks and Wildlife Management, PO Box 8365, Causeway, Zimbabwe

& R. J. Phelps Department of Zoology, University of Zimbabwe, PO Box MP 167, Harare, Zimbabwe

ABSTRACT The contents of eggs of a range of birds were analysed for residues of chlorinated hydrocarbon pesticides. Eggs collected from Harare City, and from areas where intensive agriculture was practised, showed higher residues than did eggs from regions where the form of land use was extensive agriculture, or no form of agriculture at all. Material from Lake Kariba showed considerable residue levels. Dry weight residues of p,p'DDE from the eggs of the fish eagle (31.25 mg kg- x), the peregrine falcon (62"38 mg kg- x) and the lanner falcon (16.95mgkg -x) indicate that the populations of raptors in Zimbabwe shouM be monitored carefully for indications of reproductive failure which might be attributable to pesticide residues. * Present address: c/o Triangle Ltd, P. Bag 801, Triangle, Zimbabwe. t Present address: c/o Nottingham Estates, PO Box 60, Beitbridge, Zimbabwe. 147

Environ. Pollut. Ser. B. 0143-148X/83/0005-0147/$03.00 © Applied Science Publishers Ltd, England, 1983. Printed in Great Britain

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J. Tannock, W. W. Howells, R. J. Phelps

INTRODUCTION Published data on residues of chlorinated hydrocarbon pesticides in birds' eggs in Zimbabwe are limited. Whitwell et al. (1974) provide the most information, although the monitoring of residues has continued sporadically since then. The lack of any sort of baseline against which to gauge the trend in residue levels has prompted the publication of the data presented in this paper. The Government registration scheme for pesticides was initiated in Zimbabwe in 1971, and a policy on the use of chlorinated hydrocarbon pesticides was introduced in l1973.!From this time, D D T was no longer registered for use in homes or on home gardens but continued to be registered for use on certain crops, particularly maize and cotton (B. W. Blair, pers. comm.). Chlorinated hydrocarbon pesticides were also registered for use in the control of disease vectors, particularly mosquitoes and tsetse flies. Until 1973, HCH (BHC) was the insecticide of choice for residual sprays against mosquitoes but, following the development of resistance in these insects, D D T replaced it (V. de V. Clarke, pers. comm.). Since 1969, D D T has been the insecticide used on the largest scale against tsetse flies in Zimbabwe although, prior to that time, dieldrin was used extensively in the residual insecticide approach to tsetse fly control in Zimbabwe (D. F. Lovemore, pers. comm.).

MATERIALS A N D M E T H O D S The majority of the eggs collected were blown at the time of collection and the contents were preserved in a refrigerator at - 20 °C. A few eggs were preserved whole in the same manner and the contents were removed just prior to preparation for analysis. The contents of all eggs in a nest were combined, unless otherwise indicated, and the material was blended in a Sorvall omni-mixer, freeze dried and then an aliquot of accurately determined mass was taken for analysis. Clean up of the material and the conditions under which the gas-liquid chromatography were conducted were the same as those used by Wessels et al. (1980). For comparison with results from other studies, degradation products of D D T have been converted to the proportionally equivalent value of D D T on the basis of molecular mass, and then added to any D D T residues to give a value for a total D D T equivalent.

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RESULTS AND DISCUSSION All values given are in milligrams per kilogram of residue in the egg contents on a dry mass basis. Results of the analyses conducted are given in Table 1. In cases where individual eggs in a clutch were analysed, the results fall into a narrow range of residue levels. For the purpose of large-scale surveys for pesticide residues, it appears that either a single egg from a clutch or a sample from the combined material of the whole clutch will give a reasonable indication of the magnitude of the residue in that clutch. Wankie National Park, which lies on the western boundary of Zimbabwe, is an area in which no form of agriculture is conducted and where the only human habitation is restricted to defined camping areas. Twenty-seven analyses, from nineteen clutches of birds' eggs, were made on material from the Park (Table l) and only four of these showed residues ofp,p'DDE above 1 mg k g - 1, two of the analyses being on eggs from the same nest. All of these samples came from birds associated with ponds in the Park, and these had restricted catchments. The maccoa duck and saddlebill stork may have visited a number of different ponds, including some which lie in the agricultural area to the east of the National Park. Only two analyses of the Wankie National Park material showed no detectable residues of any chlorinated hydrocarbon pesticide. The most c o m m o n residue found was that ofp,p'DDE and the widespread presence of this substance, in an area where no pesticides were used, gave an indication of the pervasive property of the metabolites of DDT. The eggs of Wahlberg's eagle and the yellow billed kite (Table 1) came from an area under indigenous hardwood forest where the use of pesticides was low. Residues detected in these eggs were low, but the variety of residues found was greater than that in Wankie National Park. This may reflect the presence of a larger human population in the forest area. Extensive agriculture, in the form of livestock and small quantities of crops grown for local consumption, was the form of land use in Tsholotsho Communal Land. Although there was a considerable human population in the area, pesticide usage under this form of land use was expected to be low. Material from the giant eagle owl egg from Tsholotsho (Table 1) contained 6 . 8 5 m g k g - 1 of p,p'DDE which indicated that D D T was being used to some extent, possibly to control

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insect pests in grain bins. Peakall & Kemp (1980) found body tissues of the spotted eagle owl Bubo africanus in South Africa to be low in chlorinated hydrocarbon residues when compared with other raptors, while other species of owls, both in Canada and South Africa, were found to have very variable levels of residues. Eggs of the peregrine falcon were collected from an intensive agricultural region of Zimbabwe. Residues of chlorinated hydrocarbon pesticides from the contents of these eggs (Table 1) show not only high levels of p,p'DDE but also appreciable levels of a range of other chlorinated hydrocarbon pesticides. The residues ofp,p'DDE in these eggs were at a level which has been associated with a decline in some populations of the peregrine falcon in other parts of the world (Hickey, 1969). Infertile eggs of a lanner falcon were collected from a window ledge of a building in Harare. These predators were known to feed on other birds resident in the city and its suburbs, but may have ranged over the intensive agricultural areas adjacent to the city. Residues of chlorinated hydrocarbon pesticides in the egg contents (Table 1) were at a level which may be deleterious to the local populations of this species. The total DDT levels for the materials analysed (Table 1) were higher than those reported by Peakall & Kemp (1976) for egg material from this species in the Transvaal. An egg from a secretary bird, a large predator, was collected on the outskirts of Harare. This bird would have foraged over a wide area around its nest, mostly in an intensive agricultural region. The chlorinated hydrocarbon pesticide levels in the egg contents (Table 1) were not unexpected for a predator in this region. Lake Kariba has a surface area of about 5250 km 2, at normal operating water level, and receives the bulk of its water from the Zambezi river, whose catchment above the lake does not include much country where intensive agriculture is conducted. There are smaller rivers entering the lake from both Zambia and Zimbabwe, some of which do drain from agricultural areas. The immediate surroundings of the lake generally do not support any form of agriculture and human populations in the region are sparse. Spraying with D D T against tsetse flies has been conducted in a number of areas near the lake. The contents of an egg of a fish eagle collected from an island in Lake Kariba showed a wide range of residues of chlorinated hydrocarbon pesticides (Table 1) of the types found in intensive agricultural areas. The level of p,p'DDE in the contents of the fish eagle egg (Table 1)

154

J. Tannock, W. W. Howells, R. J. Phelps

resembled that associated with the decline in reproduction of some populations of the American bald eagle HaliaYtus leucocephalus reported by Krantz et al. (1970). Whitwell et al. (1974) reported levels ofp,p'DDE, on a wet mass basis, in the egg contents of the reed cormorant Phalacrocorax africanus and the darter Anhinga rufra from Kariba which, if converted to residues on a dry mass basis (Lincer et al., 1981) give values of 25.5 mg kg-1 and 20.3 mg kg-1, respectively. The darter material was collected in 1971, which was prior to the start of any DDT spraying against tsetse flies in the immediate vicinity of the lake. Although no data are available on the movements offish-eating birds at Kariba, it is likely that chlorinated hydrocarbon pesticide residues have been present in birds associated with Lake Kariba since at least 1971. Up to the time of writing, there have been no scientific investigations reported which indicate a decline in any of the fish-eating bird populations on the lake. The results given in this paper indicate that further monitoring of chlorinated hydrocarbon pesticide residues in the eggs of predacious birds in Zimbabwe is needed. Studies o n the reproductive success of raptor populations should be undertaken so that any decline in populations can be detected and its cause investigated.

ACKNOWLEDGEMENTS We thank Dr J. Condy, Mr G. Davison, Mr S. A. Mitchell and the late Mr K. Fynn who collected some of the eggs, and Miss B. Mason and Mr K. Grant who assisted with the analyses. This paper is published with the permission of the Director of Research and Specialist Services and the Director of the Department of National Parks and Wildlife Management.

REFERENCES Hickey, J. J. (Ed.) (1969). Peregrine falcon populations. Their biology and decline. Madison, University of Wisconsin Press. Krantz, W. C., Mulhern, B. M., Bagley, G. E., Sprunt, A., Ligas, F. J. & Robertson, W. B. (1970). Organochlorine and heavy metal residues in bald eagle eggs. Pestic. Monit. J., 3, 136-40. Lincer, J. L., Zalkind, D., Brown, L. H. & Hopcraft, J. (1981). Organochlorine residues in Kenya's Rift Valley lakes. J. appl. Ecol., 18, 157-71.

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Peakall, D. B. & Kemp, A. C. (1976). Organochlorine residue levels in herons and raptors in the Transvaal. Ostrich, 47, 139-41. Peakall, D. B. & Kemp, A. C. (1980). Organochlorine levels in owls in Canada and South Africa. Ostrich, 51, 186-7. Wessels, C. L., Tannock, J., Blake, D. & Phelps, R. J. (1980). Chlorinated hydrocarbon insecticide residues in Crocodilus niloticus Laurentius eggs from Lake Kariba. Trans. Zimbabwe Scient. Ass., 60, 11-17. Whitwell, A. C., Phelps, R. J. & Thomson, W. R. (1974). Further records of chlorinated hydrocarbon pesticide residues in Rhodesia. Arnoldia, Rhodesia, 6(37), 1-7.