Persistent Chlorinated Pesticides in Air, Water, and Precipitation from the Lake Malawi Area, Southern Africa

Concentrations of chlorinated pesticides were analyzed in air (biweekly 1997−1998), water, and precipitation at Lake Malawi, in southeast Africa. The pesticides in air in Senga Bay on the southwest shore of Lake Malawi were not extensively weathered, implying recent use. Elevated levels of heptachlor, chlorobenzenes, aldrin, and dieldrin were detected periodically, which indicated use on a regular basis. Annual average concentrations for those pesticides ranged from 31 to 257 pg/m3. Levels of HCHs, DDTs, chlordanes, and α-endosufan in air at Senga Bay were comparable to those of the Laurentian Great Lakes, ranging from 24 to 40 pg/m3. Considering air−water gas exchange and wet deposition, the net fluxes of chlorinated pesticides to the lake surface were depositional. Concentrations of chlorinated pesticides in the water from Lake Malawi were relatively low compared to the Laurentian Great Lakes and Lake Baikal. This indicates rapid transformation of chemicals in the water column, which was further supported by high metabolite-to-parent ratios. The results suggests that tropical regions may act as both a global source and sink for chlorinated pesticides, since removal processes may be faster compared to temperate and Arctic regions.