Using solid-phase microextraction during ultrasound reveals higher aqueous PAHs release from contaminated sediment

Area of Science:

• Environmental Chemistry
• Acoustic Chemistry
• Analytical Chemistry

Background:

• Ultrasound (US) is known to release and degrade polycyclic aromatic hydrocarbons (PAHs) from contaminated sediments.
• The extent of PAH release during active US treatment versus after treatment cessation remains unclear.
• Conventional analytical methods may underestimate contaminant release by requiring treatment interruption.

Purpose of the Study:

• To quantify and compare aqueous polycyclic aromatic hydrocarbon (PAH) concentrations during and after ultrasound (US) treatment of contaminated sediment.
• To investigate the dynamic behavior of PAH desorption and re-adsorption using solid-phase microextraction (SPME).
• To evaluate the accuracy of typical analytical extraction methods in assessing US-induced contaminant release.

Main Methods:

• Solid-phase microextraction (SPME) was employed to measure aqueous PAH concentrations.
• Experimentally determined SPME fiber-water partition coefficients (KSPME).
• Sequential 10-minute exposures of SPME fibers during and after 20 kHz ultrasound application (430 W L⁻¹) to creosote-contaminated sediment.

Main Results:

• PAH desorption during active US was significantly higher compared to simple mixing.
• Aqueous concentrations of phenanthrene, anthracene, and fluoranthene were significantly higher during US than after US cessation.
• For less soluble PAHs, concentrations during US surpassed expected equilibrium levels, with subsequent re-adsorption onto sediment after US was stopped.

Conclusions:

• Ultrasound treatment significantly enhances the release of PAHs from contaminated sediments during active application.
• PAH concentrations during US can exceed equilibrium predictions, indicating a temporary but significant increase in bioavailability.
• Analytical methods that halt US treatment before sampling may underestimate the true contaminant release potential of this technology.