Lin Chen-Hung Michael, Pedersen Joel A, Suffet Irwin H
Department of Environmental Health Sciences, University of California, Los Angeles, California 90095, USA.
Environ Sci Technol. 2003 Aug 15;37(16):3547-54. doi: 10.1021/es026048p.
Dredging operations, resuspension events during storms, and bioturbation alter the oxic state of estuarine sediments and induce changes in the composition of dissolved and particle-associated natural organic matter. These changes may alter the distribution of hydrophobic organic chemicals (HOCs) in sediments and their diffusive flux across the sediment-water interface. In this study, the impact of aerating anoxic sediments on the distribution and diffusive flux of a model HOC, 2,2',4,4'-tetrachlorobiphenyl (TeCB), was investigated. Anoxic estuarine sediments collected from three sites along a salinity gradient were used to determine site-specific apparent sorption coefficients for porewater dissolved organic carbon (Kpwdoc) and sediment organic carbon (Koc) under anoxic and oxic conditions. A two-compartment sediment flux model was employed to examine the diffusive flux of TeCB under both oxic states. Aeration of anoxic porewaters resulted in significant decreases in porewater dissolved organic matter (DOMpw) aromaticity as indicated by declines in molar absorptivity at 254 nm (p < 0.005). Aeration also resulted in a 9-13% decrease in DOMpw concentration (p < 0.005) at the two sites exhibiting lower ionic strengths; the high ionic strength site did not exhibit a significant change in DOMpw concentration (p > 0.10). The impact of aeration on TeCB distribution and diffusive flux appeared to be site-specific. Aeration of anoxic sediments induced a significant 1.4 log unit reduction in Kpwdoc at the lowest ionic strength site (p < 0.0005), while sediments from the intermediate ionic strength site exhibited a significant 0.6 log unit increase (p < 0.005). No significant change in sorption to DOMpw was observed for the high ionic strength site (p > 0.10). The sediment displaying the drop in Kpwdoc also exhibited a significant 0.4 log unit drop in Koc (p < 0.01), while the other two sites did not exhibit significant aeration-induced changes in sorption to particle-associated organic matter (p > 0.10). No significant change in diffusive flux was observed for two sites (p > 0.10), while a significant 89-110 mg m(-2) yr(-1) increase in diffusive flux was observed at the low ionic strength site (p < 0.10). This latter result represented approximately a doubling in diffusive flux. In the systems studied, facilitation of TeCB transport across the sediment-water interface by organic colloids did not appear important.
疏浚作业、风暴期间的再悬浮事件以及生物扰动会改变河口沉积物的氧化状态，并引起溶解态和颗粒态天然有机物组成的变化。这些变化可能会改变疏水性有机化学品（HOCs）在沉积物中的分布及其通过沉积物 - 水界面的扩散通量。在本研究中，考察了对缺氧沉积物进行曝气对一种典型HOC——2,2',4,4'-四氯联苯（TeCB）的分布和扩散通量的影响。使用从沿盐度梯度的三个地点采集的缺氧河口沉积物，来测定缺氧和有氧条件下孔隙水溶解有机碳（Kpwdoc）和沉积物有机碳（Koc）的特定地点表观吸附系数。采用双室沉积物通量模型来研究TeCB在两种氧化状态下的扩散通量。对缺氧孔隙水进行曝气导致孔隙水溶解有机物（DOMpw）的芳香性显著降低，这表现为254 nm处摩尔吸光系数下降（p < 0.005）。曝气还导致在离子强度较低的两个地点DOMpw浓度下降了9 - 13%（p < 0.005）；离子强度高的地点DOMpw浓度没有显著变化（p > 0.10）。曝气对TeCB分布和扩散通量的影响似乎具有地点特异性。在离子强度最低的地点，对缺氧沉积物进行曝气导致Kpwdoc显著降低1.4个对数单位（p < 0.0005），而离子强度中等的地点的沉积物则显著增加0.6个对数单位（p < 0.005）。离子强度高的地点对DOMpw的吸附没有显著变化（p > 0.10）。Kpwdoc下降的沉积物的Koc也显著下降0.4个对数单位（p < 0.01），而其他两个地点对颗粒态有机物的吸附没有因曝气而发生显著变化（p > 0.10）。两个地点的扩散通量没有显著变化（p > 0.10），而在离子强度低的地点观察到扩散通量显著增加89 - 110 mg m(-2) yr(-1)（p < 0.10）。后一结果表示扩散通量大约增加了一倍。在所研究的系统中，有机胶体促进TeCB通过沉积物 - 水界面的传输似乎并不重要。
