Biotransformation of Chemicals at the Water-Sediment Interface-Toward a Robust Simulation Study Setup

Area of Science:

• Environmental Chemistry
• Microbiology
• Ecotoxicology

Background:

• Standardized aquatic biotransformation studies (OECD 308, OECD 309) are crucial for environmental risk assessment of chemicals.
• Existing OECD guidelines exhibit variable outcomes and questionable environmental relevance, necessitating improved test systems.
• Persistent chemicals in natural waters pose risks, driving the need for reliable biotransformation testing.

Purpose of the Study:

• To evaluate a modified biotransformation test system with an aerated water column over a thin sediment layer.
• To address shortcomings of standard OECD 308/309 studies, focusing on variability and environmental relevance.
• To investigate microbial community dynamics and their influence on chemical biotransformation.

Main Methods:

• A modified aquatic biotransformation test system was developed and characterized.
• Forty-three diverse chemical compounds (pharmaceuticals, pesticides, sweeteners) were tested.
• Multidimensional flow cytometry and machine learning were used to analyze microbial communities in water and sediment.

Main Results:

• The modified system demonstrated reduced inter-replicate variability and improved biotransformation observability compared to standard OECD 308/309.
• First-order biotransformation kinetics were observed for most test compounds.
• Sediment-associated microbial communities were more stable and diverse than water-column communities.

Conclusions:

• Aquatic chemical biotransformation is most robustly studied in systems with sufficient sediment-borne microbial biomass.
• Modified OECD 308-type systems with optimized sediment-water ratios are favored over OECD 309 for studying the water-sediment interface.
• Understanding microbial community behavior is key to interpreting and improving biotransformation test results.