The present study shows the occurrence of 2,2',3,3',4,4',5,5',6,6'-decabromodiphenyl ether (BDE-209) in microbial biofilms of Pyrenean and Tatra high mountain lakes despite its low vapor pressure and high hydrophobicity. Aerosol air transport is therefore a feasible mechanism for BDE-209 accumulation in sites up to 2688 m above sea level. This compound and other PBDEs exhibit altitudinally-dependent distribution involving higher concentrations with increasing mountain lake elevation. However, the apparently very high enthalpies of the concentration gradients observed, including BDE-209, suggest that bacterial anaerobic debromination also plays a significant role in the resulting altitudinal distributions. This microbial mechanism explains the relative abundances of PBDEs and their within lake differences between rocky and sediment microbial biofilms, thereby showing that the altitudinal pattern observed is not purely due to water temperature control on bacterial activity but also to changes in the availability of anaerobic microenvironments which increase with increasing lake productivity at lower altitudes.
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