Field Observation and Modeling of Dissolved Fraction Sediment-Water Exchange Coefficients for PCBs in the Hudson River
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- 作者：Michael J. Erickson ; Carrie L. Turner ; and Louis J. Thibodeaux
- 刊名：Environmental Science & Technology
- 出版年：2005
- 出版时间：January 15, 2005
- 年：2005
- 卷：39
- 期：2
- 页码：549 - 556
- 全文大小：229K
- 年卷期：v.39,no.2(January 15, 2005)
- ISSN：1520-5851
文摘
Chemical fate and transport models that simulatesediment-water exchange of contaminants typicallyemploy empirically determined sediment-water exchangecoefficients for the dissolved fraction to describe thenet effect of poorly understood mechanisms. This paperpresents field-derived observations of the coefficient for 12PCB congeners and two PCB mixtures in the ThompsonIsland Pool, Hudson River, and also presents an evaluationof a theoretical sediment-water exchange model. Anextensive PCB data set was used to compute apparentcoefficients for PCBs in the pool. Average exchangecoefficients for the 12 congeners ranged from 2.6 to 18.8 cm/day, and results showed a strong seasonal dependence.Peak coefficient values occurred in mid-May to early July,preceding peak water temperatures by 1 month andlagging the spring high-flow period. The coefficientsincrease with increasing partition coefficients, suggestinga dependence on congener properties. The largemagnitude of the coefficients and the variation among thecongeners is inconsistent with the pore-water molecular-diffusion transport process. A theory-based, mechanistic two-layer model reproduces the nonlinear relationship betweenthe sediment-water exchange coefficients and partitioncoefficients. This model includes transfer through the mixedsediment layer by bioturbation and diffusion transferthrough a water-side boundary layer governed by flowvelocity. Results suggest that this algorithm can provideincreased accuracy to future system-level fate and transportmodels for hydrophobic chemicals. The seasonal variationin the transfer coefficient appears to be a poorlyunderstood interaction of physical and biological processesand merits further study.