Microbial degradation is a key elimination pathway of hexachlorocyclohexanes from the Arctic Ocean
ABSTRACT Hexachlorocyclohexanes (HCHs) are the most abundant pesticides in arctic air and water. We have calculated in situ microbial degradation rates of α- and γ-HCH for the Arctic Ocean using enantiomer ratio (ER) data and concentrations in water at the surface and after it has subducted to depth. The ERs of α-HCH, which provide the first direct evidence of microbial degradation, allow rates to be estimated. The half-lives due to microbial activity for (+)-α-HCH, (−)-α-HCH and γ-HCH (respectively 5.9 ± 1.2, 22.8 ± 4.7 and 18.8 ± 10.1 years) are 3–10 times faster than removal by the only other known breakdown mechanism, hydrolysis (Harner et al., 1999). Microbial degradation is highlighted as an important elimination process in a revised HCH loss budget for the Arctic Ocean, removing 204 t y−1, α-HCH and 23 t y−1, γ-HCH. These tonnages represent 29–37% of the annual HCH removal from the Arctic Ocean.
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ABSTRACT: POPs in the Arctic are the focus of international concern due to their occurrence and accumulation in Arctic food webs. This paper presents an overview of the major pathways into the Arctic and details contemporary studies that have focused on the occurrence and transfer of POPs between the major Arctic compartments, highlighting areas where there is a lack of quantitative information. The behaviour of these chemicals in the Arctic atmosphere is scrutinised with respect to long-term trends and seasonal behaviour. Subtle differences between the PCBs and OC pesticides are demonstrated and related to sources outside of the Arctic as well as environmental processes within the Arctic. Unlike temperate regions, contaminant fate is strongly affected by the presence of snow and ice. A description of the high Arctic snow pack is given and the physical characteristics that determine chemical fate, namely the specific surface area of snow and wind driven ventilation, are discussed. Using a well-characterised fresh snow event observed at Alert (Canadian high Arctic) [Atmos. Environ. 36(2002) 2767] the flux of gamma-HCH out of the snow is predicted following snow ageing. Under conditions of wind (10 m/s) it is estimated that approximately 75% of the chemical may be re-emitted to the atmosphere within 24 h following snowfall, compared with just approximately 5% under conditions of no wind. The implications of this are raised and areas of further research suggested.Environmental Pollution 02/2004; 128(1-2):163-75. · 3.73 Impact Factor
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