R.M. Parsons Laboratory, Department of Civil and Environmental Engineering , Massachusetts Institute of Technology , Cambridge , Massachusetts 02139 , United States.
Department of Environmental Sciences, Huxley College of the Environment , Western Washington University , Bellingham , Washington 98225 , United States.
Environ Sci Technol. 2018 Apr 17;52(8):4565-4573. doi: 10.1021/acs.est.7b05809. Epub 2018 Apr 9.
Polychlorinated biphenyl (PCB) fluxes from contaminated sediments can be caused by mechanisms including diffusion, bioirrigation, and resuspension, but it is often unclear which mechanisms are important. In the Lower Duwamish Waterway (Seattle, Washington), the presence of abundant benthic macrofauna suggests that porewater bioirrigation may be an important mechanism for PCB transport from the bed into the overlying water column. In this field study, the fluxes of PCBs due to bioirrigation were quantified by using (a) polyethylene (PE) samplers to quantify in situ and ex situ (i.e., equilibrium) PCB porewater concentration profiles and (b) measurements of the geochemical tracer Rn to quantify the rate of porewater exchange with overlying water. The results showed that bioirrigation caused sorptive disequilibrium with the surrounding sediment, which led to lower in situ porewater concentrations than expected from sediment concentrations. The combined fluxes of seven PCB congeners (ΣPCBs) were 1.6-26 ng/m/day for the three field sites, similar in magnitude to the upper limit estimates of diffusive fluxes calculated assuming water-side boundary layer control (ΣPCBs = 1.3-47 ng/m/day). Moreover, the depleted in situ porewater concentrations imply lower diffusive flux estimates than if the ex situ porewater concentrations had been used to estimate fluxes (ΣPCBs = 89-670 ng/m/day). These results suggest that nondiffusive PCB fluxes from the sediment bed are occurring and that quantifying in situ porewater concentrations is crucial for accurately quantifying both diffusive and nondiffusive PCB fluxes.
多氯联苯 (PCB) 从污染沉积物中的通量可以通过扩散、生物搅动和再悬浮等机制引起，但通常不清楚哪些机制是重要的。在低杜瓦米什水道（华盛顿州西雅图），丰富的底栖大型动物的存在表明，孔隙水生物搅动可能是 PCB 从床层向覆盖水柱迁移的重要机制。在这项野外研究中，通过使用 (a) 聚乙烯 (PE) 采样器来量化原位和异位（即平衡）PCB 孔隙水浓度分布，以及 (b) 测量地球化学示踪剂 Rn 来量化孔隙水与上覆水的交换速率，量化了由于生物搅动而导致的 PCB 通量。结果表明，生物搅动导致与周围沉积物的吸附不平衡，从而导致原位孔隙水浓度低于从沉积物浓度推断出的预期浓度。三个野外地点的七种 PCB 同系物（ΣPCBs）的综合通量为 1.6-26 ng/m/天，与假设水侧边界层控制（ΣPCBs = 1.3-47 ng/m/天）计算得出的扩散通量上限估计值相当。此外，原位孔隙水浓度的消耗意味着如果使用异位孔隙水浓度来估计通量，扩散通量的估计值会更低（ΣPCBs = 89-670 ng/m/天）。这些结果表明，正在发生非扩散性 PCB 从沉积物床层的通量，并且量化原位孔隙水浓度对于准确量化扩散性和非扩散性 PCB 通量至关重要。
