Organochlorine residues in Kenya's Rift Valley lakes.
In studies on organochlorine residues in lakes of the Rift Valley, Kenya, 47% of the farms surveyed in the Nakuru catchment basin used either DDT or dieldrin for the control of cereal pests. The most commonly used acaricide (for cattle tick control) was toxaphene, followed by dioxathion. The largest single source of pesticides in the Nakuru basin was probably the town of Nakuru (for mosquito, weed and rodent control, dog washes, stored-grain protection, and household pest control). DDE residue levels were fairly low compared with those in similar habitats in other parts of the world. Very low, undetectable or trace levels of DDE were found in algae and Tilapia from Lake Naivasha, algae and corixid larvae from Lake Nakuru, and vegetation from Lake Baringo. Of the bird eggs sampled, the lowest DDE levels were found in Lake Naivasha cattle egrets (Bubulcus ibis) (0.22 mg/litre) and the highest in the Lake Nakuru African darter (Anhinga rufa) (5.75 mg/litre). Of the 4 lakes studied, Elmenteita was possibly the most heavily contaminated. 'Biological magnification' was observed in some food chains studied.