Wania Frank
Department of Physical and Environmental Sciences, University of Toronto Scarborough, 1265 Military Trail, Toronto, Ontario, Canada M1C 1A4.
Environ Sci Technol. 2007 Jul 1;41(13):4529-35. doi: 10.1021/es070124c.
Whereas the pervasive and abundant presence of perfluorinated carboxylic acids (PFCAs) in the Arctic marine food chain is clearly established, their origin and transport pathway into the Arctic Ocean are not. Either the atmospheric oxidation of volatile precursor compounds, such as the fluorotelomer alcohols (FTOHs), or the long-range oceanic transport of directly emitted PFCAs is seen as contributing the bulk of the PFCA input to the Arctic. Here simulations with the zonally averaged global fate and transport model Globo-POP, in combination with historical emission estimates for FTOHs and perfluorooctanoic acid (PFOA), are used to evaluate the relative efficiency and importance of the two transport pathways. Estimates of the emission-independent Arctic Contamination Potential reveal that the oceanic transport of directly emitted PFCAs is more than 10-fold more efficient than the atmospheric degradation of FTOHs in delivering PFCAs to the Arctic, mostly because of the low yield of the reaction. The cumulative historic emissions of FTOHs are lower than those estimated for PFOA alone by a factor of 2-3, further limiting the contribution that precursor oxidation makes to the total PFCAs load in the Arctic Ocean. Accordingly, when fed only with FTOH emissions, the model predicts FTOH air concentrations in agreement with the reported measurements, but yields Arctic seawater concentrations for the PFOA that are 2 orders of magnitude too low. Whereas ocean transport is thus very likely the dominant pathway of PFOA into the Arctic Ocean, the major transport route of longer chain PFCAs depends on the size of their direct emissions relative to those of 10:2 FTOH. The predicted time course of Arctic seawater concentrations is very similar for directly emitted and atmospherically generated PFCAs, implying that neither past doubling times of PFCA concentrations in Arctic marine mammals nor any future time trends are likely to resolve the question of the dominant source of PFCAs.
虽然全氟羧酸（PFCA）在北极海洋食物链中普遍且大量存在已得到明确证实，但其进入北冰洋的来源和传输途径尚不清楚。挥发性前体化合物（如氟调聚物醇，FTOH）的大气氧化，或直接排放的PFCA的长距离海洋传输，都被视为北极PFCA输入的主要来源。在这里，利用纬向平均全球归宿和传输模型Globo - POP，并结合FTOH和全氟辛酸（PFOA）的历史排放估算，来评估这两种传输途径的相对效率和重要性。与排放无关的北极污染潜力估算表明，直接排放的PFCA的海洋传输在将PFCA输送到北极方面比FTOH的大气降解效率高10倍以上，这主要是因为反应产率较低。FTOH的累积历史排放量比仅PFOA的估算值低2至3倍，进一步限制了前体氧化对北冰洋总PFCA负荷的贡献。因此，当仅输入FTOH排放时，该模型预测的FTOH空气浓度与报告的测量值一致，但得出的北极海水中PFOA的浓度比实际值低2个数量级。虽然海洋传输很可能是PFOA进入北冰洋的主要途径，但长链PFCA的主要传输路线取决于其直接排放量与10:2 FTOH排放量的相对大小。对于直接排放和大气生成的PFCA，预测的北极海水浓度随时间变化的过程非常相似，这意味着北极海洋哺乳动物体内PFCA浓度过去的倍增时间或未来的任何时间趋势都不太可能解决PFCA主要来源的问题。
