The effect of dieldrin, sprayed by aerial application for tsetse control, on game animals.
Abstract
The large-scale use of organochlorine compounds in insect control causes increasing concern due to their toxicity and persistance which creates environmental problems. Dieldrin has been widely been used in insect control and was chosen for a control trial of Glossina spp. (mainly G. pallidipes Newst.) in the Lambwe Valley, Kenya, in 1968-71. Throughout these trials, resident wildlife populations were monitored in order that potential short and long term hazards from the insecticide could be assessed. The conversion of dieldrin, under tropical conditions, to a more acutely toxic photo-isomer was also considered. Brain, liver and kidney samples were taken from two antelope species (reedbuck and oribi), before, immediately and several months after the airspray trials. Brain and liver samples were taken from two carnivore species (hyaena and civet). These tissues together with soil and grass samples were analysed by gas liquid chromatography to assess dieldrin and isomer residue levels. Game censuses and post-mortem examinations were also carried out to assess acute toxic affects.The photo-isomerisation of dieldrin did not increase the short- or long-term hazard of this insecticide to wildlife. With a few exceptions, insecticide levels in game tissues immediately after the aerial application of dieldrin at 144 g/ha to the collection area remained below those considered hazardous to the animals' health. Less than two years after spraying 409 g/ha, the residues in animal tissues and on exposed vegetation had returned to prespray levels. The photoisomerisation of dieldrin did not increase the short or long term hazard of this insecticide to wildlife.