Direct visualization of pyrene diffusion in polyethylene and polyoxymethylene passive samplers

Area of Science:

• Environmental Chemistry
• Polymer Science
• Analytical Chemistry

Background:

• Passive sampling is crucial for analyzing ultra-low concentrations of hydrophobic organic compounds in environmental water.
• Fundamental diffusive processes in polymers used for passive sampling are not well understood.
• Accurate modeling of diffusion is needed to improve the reliability of passive sampling techniques.

Purpose of the Study:

• To investigate and understand the fundamental diffusive processes of hydrophobic organic compounds in polymers.
• To model the diffusion of a model compound, pyrene, in polyethylene (PE) and polyoxymethylene (POM).
• To evaluate the suitability of different polymers for passive sampling applications based on their diffusion characteristics.

Main Methods:

• Used pyrene as a model hydrophobic organic compound.
• Directly tracked pyrene penetration into PE and POM rods via microscopy after absorption from water.
• Simulated diffusion profiles using numerical integration of Fickian diffusion models.

Main Results:

• Pyrene uptake in PE followed Fick's law, with similar absorption and desorption kinetics.
• Pyrene uptake in POM exhibited non-Fickian behavior, with slower release kinetics than uptake.
• Slower desorption from POM complicates the use of performance reference compounds (PRCs) for nonequilibrium corrections in dynamic environments.

Conclusions:

• Polyethylene is suitable for passive sampling due to Fickian diffusion and balanced kinetics.
• Polyoxymethylene's non-Fickian behavior and slow desorption present challenges for passive sampling corrections in environments with advection.
• Despite hysteretic behavior, POM may still be useful for static sediment deployments where transport is slow.