Sensitive equilibrium sampling to study polychlorinated biphenyl disposition in Baltic Sea sediment

Area of Science:

• Environmental Chemistry
• Analytical Chemistry
• Ecotoxicology

Background:

• Polychlorinated biphenyls (PCBs) are persistent organic pollutants with significant environmental and health concerns.
• Accurate measurement of freely dissolved concentrations in sediment is crucial for risk assessment.
• Existing methods for trace-level hydrophobic chemical analysis in complex matrices like sediment are challenging.

Purpose of the Study:

• To validate and apply an equilibrium sampling method using polydimethylsiloxane (PDMS) coated glass jars for analyzing PCBs in sediment.
• To determine freely dissolved PCB concentrations (C(Sediment_free)) in sediment interstitial porewater.
• To assess sediment-water and sediment-biota equilibrium, and site-specific sediment/water distribution ratios (K(D)).

Main Methods:

• Utilized glass jars with thin polydimethylsiloxane (PDMS) coatings for equilibrium sampling.
• Applied the method to sediment samples from a >50 km transect in the Stockholm Archipelago.
• Demonstrated equilibrium between sediment and PDMS using varying coating thicknesses.

Main Results:

• Stockholm Harbor showed significantly higher C(Sediment_free) for PCBs, indicating it as a source to the Baltic Sea.
• Fugacity in sediment exceeded that in water by a factor of 4.0 and in herring by 5.2.
• Sediment/water distribution ratios (K(D)) were higher near Stockholm Harbor compared to the outer archipelago.

Conclusions:

• The PDMS coated glass jar method provides high precision and built-in QA/QC for trace-level analysis of hydrophobic chemicals.
• The method enables new possibilities for studying chemical disposition in background environments.
• The study highlights Stockholm as a significant source of PCBs impacting the Baltic Sea ecosystem.