Explaining PAH desorption from sediments using Rock Eval analysis

Area of Science:

• Environmental Chemistry
• Geochemistry
• Sedimentology

Background:

• Polycyclic Aromatic Hydrocarbons (PAHs) are persistent organic pollutants in river systems.
• Understanding PAH sorption and desorption is crucial for environmental risk assessment.
• River sediments act as sinks and sources for PAHs, influencing their environmental fate.

Purpose of the Study:

• To evaluate Rock Eval residual carbon (RC) and black carbon (BC) as predictors of PAH desorption kinetics in river sediments.
• To determine the suitability of single versus dual domain sorption models for PAH distribution coefficients (KD).
• To identify a relevant sediment characteristic for assessing PAH bioavailability and risk.

Main Methods:

• Rock Eval analysis for residual carbon (RC) and black carbon (BC) characterization.
• Sequential Tenax extractions to determine PAH desorption kinetic parameters.
• Calculation of polycyclic aromatic hydrocarbon distribution coefficients (KD).
• Statistical modeling (single vs. dual domain) to explain KD.

Main Results:

• Residual carbon (RC) adequately predicts fast, slow, and very slow desorbing fractions of 4-ring PAHs.
• RC showed a stronger correlation with PAH desorption than BC (BC constituted only 7% of RC).
• A dual domain sorption model best explained KD for low molecular weight PAHs, while a single domain model was better for high molecular weight PAHs.

Conclusions:

• Residual carbon (RC) is a relevant sediment characteristic for predicting the bioavailability of 4-ring PAHs.
• RC is a superior predictor compared to black carbon (BC) for sediment-bound PAH risk assessment.
• The findings support the use of RC in environmental monitoring and risk management of contaminated river sediments.