In Situ Passive Sampling to Monitor Long Term Cap Effectiveness at a Tidally Influenced Shoreline.

Alex Smith,Danny Reible,William Gardiner,Xiaolong Shen,Uriel Garza-Rubalcava

doi:10.3390/toxics10030106

Alex Smith, Danny Reible + Show 3 more

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https://doi.org/10.3390/toxics10030106

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Abstract

Polydimethylsiloxane solid-phase microextraction passive samplers were used to evaluate long-term performance of a sand/gravel cap placed in 2005 in a tidally influenced shoreline in Puget Sound to reduce polycyclic aromatic hydrocarbon (PAH) transport into overlying surface water. Sampling in both 2010 and 2018 measured porewater concentrations of <1 ng/L total PAHs in the cap layer. d-PAH performance reference compounds were used to evaluate the extent of equilibration of the contaminants onto the samplers and to estimate net upwelling velocities through a mass-transfer model. The upwelling velocities were used to predict long-term migration of selected PAHs through the cap, showing that the cap is expected to continue being effective at limiting exposure of contaminants at the cap–water interface.

Highlights

Monitor Long Term Cap EffectivenessContaminated sediment caps physically isolate environmental contamination and delay or eliminate significant release of hydrophobic organic compounds (HOCs)
Three-ring and larger polycyclic aromatic hydrocarbon (PAH) generally totaled less than 50 ng/L in 2010
The PAHs observed in the northwestern zone in 2010 were likely associated with sediment intermixed into the cap during placement in 2005 or as a result of equilibration with overlying water

Summary

Introduction

Monitor Long Term Cap EffectivenessContaminated sediment caps physically isolate environmental contamination and delay or eliminate significant release of hydrophobic organic compounds (HOCs). In the absence of advection, transport below surface layers is driven by sorption-retarded diffusion and long-term effectiveness is typically observed [1,2]. Evaluating the effect of these processes is a critical component of long-term monitoring of cap effectiveness. Dissolved concentrations of HOCs can be measured via passive sampling, e.g., by solid-phase microextraction (SPME) utilizing polydimethylsiloxane (PDMS) as a sorbent [3]. Dissolved concentrations provide an indication of the contaminant that is mobile and available in a stable sediment cap. Previous studies have demonstrated the use of passive sampling to estimate concentrations influencing the benthic community in surficial sediments [4,5], and calculating the diffusive flux at the sediment–water interface [6,7]

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