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Perfluorooctane sulfonate (PFOS) adsorption on Fe-rich mineral assemblages and soils: experiments and surface
Devin Farrell1, Zoi Dokou2, Nefeli Bompoti3
1Department of Civil and Environmental Engineering, College of Engineering, University of Massachusetts Dartmouth, North Dartmouth, 02747, MA, United States.
Geochemical Transactions
|November 21, 2025
Summary
Perfluorooctane sulfonate (PFOS) adsorption on minerals and soils depends on pH. At low pH, ferrihydrite dominates retention via outer-sphere complexation, while at high pH, quartz surfaces drive hydrophobic partitioning, impacting contaminant transport.
Area of Science:
- Environmental Chemistry
- Geochemistry
- Environmental Science
Background:
- Perfluorooctane sulfonate (PFOS) is a persistent environmental contaminant with significant mobility in subsurface environments.
- PFOS contamination poses risks to human health and ecosystems, necessitating research into its environmental fate and transport.
- Understanding PFOS adsorption mechanisms is crucial for predicting its behavior and developing effective remediation strategies.
Purpose of the Study:
- To investigate the adsorption behavior of PFOS on various solid substrates, including ferrihydrite, ferrihydrite-coated sand, and natural soil.
- To elucidate the influence of geochemical conditions, particularly pH, on PFOS retention mechanisms.
- To integrate experimental data with surface complexation modeling (SCM) and component additivity approaches for a comprehensive understanding of PFOS transport.
Main Methods:
- Batch adsorption experiments were conducted using ferrihydrite, ferrihydrite-coated sand, and soil from a PFOS-impacted site.
- Surface complexation modeling (SCM) was employed to analyze adsorption mechanisms.
- The component additivity approach was applied to evaluate the contributions of different mineral phases to PFOS retention.
Main Results:
- PFOS adsorption was significant on both ferrihydrite and quartz surfaces, with ferrihydrite-coated sand and soil showing combined effects.
- At acidic pH (<5.5 for ferrihydrite-coated sand, <6.0 for soil), PFOS retention was dominated by outer-sphere complexation at ferrihydrite surfaces.
- At neutral to alkaline pH, hydrophobic interactions with quartz surfaces became the primary sorption mechanism, indicating a shift from charge-driven to partitioning-driven retention.
Conclusions:
- The study identified distinct pH-dependent sorption mechanisms governing PFOS behavior in subsurface environments.
- Variability in traditional partitioning coefficients (Kd) correlates with shifts in dominant surface complexation and partitioning.
- Enhanced predictive models incorporating these mechanisms are essential for accurate risk assessment and management of PFOS-contaminated sites.
