4.0 Article

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

Journal

ACS ENVIRONMENTAL AU
Volume 1, Issue 1, Pages 46-57

Publisher

AMER CHEMICAL SOC
DOI: 10.1021/acsenvironau.1c00006

Keywords

biotransformation; micropollutants; chemicalpersistence; water-sediment systems; phenotypicmicrobial community composition; cell type diversity; OECD 308; 309 studies

Funding

  1. German Federal Ministry for the Environment, Nature Conservation and Nuclear Safety [FKZ 3717 65 409 0]

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The study found that improvements in the biotransformation test system resulted in better repeatability, observability and consistency in studying the biotransformation of various compounds. By analyzing different cell densities and diversities, it was revealed that microbial communities in sediment were more stable with higher cell type diversity.
Studying aquaticbiotransformation of chemicals in laboratory experiments,i.e., OECD 308 and OECD 309 studies, is required by internationalregulatory frameworks to prevent the release of persistent chemicalsinto natural water bodies. Here, we aimed to address several previouslydescribed shortcomings of OECD 308/309 studies regarding their variableoutcomes and questionable environmental relevance by broadly testingand characterizing a modified biotransformation test system in whichan aerated water column covers a thin sediment layer. Compared tostandard OECD 308/309 studies, the modified system showed little inter-replicatevariability, improved observability of biotransformation, and consistencywith first-order biotransformation kinetics for the majority of 43test compounds, including pharmaceuticals, pesticides, and artificialsweeteners. To elucidate the factors underlying the decreased inter-replicatevariability compared to OECD 309 outcomes, we used multidimensionalflow cytometry data and a machine learning-based cell type assignmentpipeline to study cell densities and cell type diversities in thesediment and water compartments. Our here presented data on cell typecomposition in both water and sediment allows, for the first time,to study the behavior of microbial test communities throughout differentbiotransformation simulation studies. We found that sediment-associatedmicrobial communities were generally more stable throughout the experimentsand exhibited higher cell type diversity than the water column-associatedcommunities. Consistently, our data indicate that aquatic biotransformationof chemicals can be most robustly studied in test systems providinga sufficient amount of sediment-borne biomass. While these findingsfavor OECD 308-type systems over OECD 309-type systems to study biotransformationat the water-sediment interface, our results suggest that theformer should be modified toward lower sediment-water ratiosto improve observability and interpretability of biotransformation.

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