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/m 3 . Levels of HCHs, DDTs, chlordanes, and R-endosufan in air at Senga Bay were comparable to those of the Laurentian Great Lakes, ranging from 24 to 40 pg/m 3 . 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.

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Concentrations of achiral and chiral organochlorine contaminants (OCs), including hexachlorocyclohexane isomers (HCH), chlordane congeners (cis- and trans-chlordane, cis- and trans-nonachlor, MC5, MC7, and U82), and related metabolites (oxychlordane [OXY] and heptachlor exo-epoxide [HEPX]), were quantified in seawater (100 L; n = 6) and biota from the coastal Beaufort-Chukchi Seas food web near Barrow (AK, USA). The biota included zooplankton (Calanus spp.; n = 5), fish species such as arctic cod (Boreogadus saida; n = 10), arctic char (Salvelinus alpinus; n = 3), and marine mammals including bowhead whales (Balaena mysticetus; liver: n = 23; blubber: n = 40), beluga whales (Delphinapterus leucas; blubber: n = 20), ringed seals (Phoca hispida; blubber: n = 20), and bearded seals (Erignathus barbatus; blubber: n = 7). The food web magnification factors (FWMFs) for HCHs and chlordane compounds ranged from 0.5 (gamma-HCH) to 6.5 (HEPX) and were expected based on known recalcitrance and biotransformation of OCs. The enantiomer fractions (EFs) of all chiral OCs were near racemic (EF = 0.50) in the seawater, zooplankton, and all fish analyzed. In contrast, the EFs for most OCs analyzed were nonracemic (EF # 0.50) in the marine mammals blubber (range: 0.09-0.79) because of enantiomer-specific biotransformation and (or) accumulation. However, EF values were not significantly correlated with isotopically determined trophic level. The EFs for all chiral OCs (except alpha-HCH) in bowhead whale liver closely approximated the values in zooplankton, suggesting that the accumulation of chiral OCs from prey into this cetacean is not enantiomer specific. However, the modification of EFs from bowhead liver to blubber suggests that this species has the ability to enantioselectively biotransform and accumulate several chiral OC compounds.

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