Mixture Risk Drivers in Freshwater Sediments and Their Bioavailability Determined Using Passive Equilibrium Sampling.

Area of Science:

• Environmental Chemistry
• Ecotoxicology
• Risk Assessment

Background:

• Sediment risk assessment faces challenges in identifying mixture risk drivers, particularly concerning bioavailability.
• Bioavailability is crucial as it determines the fraction of contaminants accessible to organisms.

Purpose of the Study:

• To assess the bioavailability of organic contaminants in sediments using polydimethylsiloxane (PDMS).
• To characterize the toxicological and chemical profiles of both whole sediment and bioavailable fractions.
• To identify the drivers of mixture effects in sediments, considering both legacy and present-use chemicals.

Main Methods:

• Equilibrium partitioning using PDMS to access bioavailable contaminants.
• In vitro reporter gene assays for toxicological characterization.
• Liquid and gas chromatography coupled to high-resolution mass spectrometry for chemical analysis.

Main Results:

• Bioavailable fractions of mixture effects and chemicals were generally low (<0.1), suggesting strong binding.
• Detected chemicals explained only a small fraction of observed biological effects in both whole sediments and bioavailable extracts.
• Mixture effects were driven by both legacy pollutants (e.g., PAHs) and present-use chemicals (e.g., plastic additives).

Conclusions:

• A significant portion of sediment-bound chemicals may not pose an immediate ecotoxicological risk but could be remobilized over time.
• Current analytical methods may underestimate the contribution of bioavailable contaminants to overall mixture toxicity.
• Comprehensive sediment risk assessment requires diverse bioassays, a broad range of contaminants, and consideration of bioavailability.