Biodegradation of chemicals tested in mixtures and individually: mixture effects on biodegradation kinetics and microbial composition

Heidi Birch*, Arnaud Dechesne, Karina Knudsmark Sjøholm, Philipp Mayer

*Corresponding author for this work

Research output: Contribution to journalJournal articleResearchpeer-review


Biodegradation in the aquatic environment occurs in the presence of many chemicals, while standard simulation biodegradation tests are conducted with single chemicals. This study aimed to investigate the effect of the presence of additional chemicals on (1) biodegradation kinetics of individual chemicals and (2) the microbial composition in test systems. Parallel mixture and single substance experiments were conducted for 9 chemicals (phenethyl benzoate, oxacycloheptadec-10-en-2-one, α-ionone, methyl 2-naphthyl ether, decan-5-olide, octan-2-one, 2′-acetonaphthanone, methyl N-methylanthranilate, (+)-menthone) using inoculum from a Danish stream. Biotic and abiotic test systems were incubated at 12 °C for 1–30 days. Primary biodegradation kinetics were then determined from biotic/abiotic peak area ratios using SPME GC/MS analysis. The effect of the mixture on biodegradation varied with test chemical and was more pronounced for chemicals with lag-phases above 14 days: two chemicals degraded in the mixture but not when tested alone (i.e., positive mixture effect), and two degraded when tested alone but not in the mixture (i.e., negative mixture effect). Microbial composition (16S rRNA gene amplicon sequencing) was highly affected by 14 days incubation and the presence of the mixture (significant carbon source), but less by single chemicals (low carbon source). Growth on chemical mixtures resulted in consistent proliferation of Pseudomonas and Malikia, while specific chemicals increased the abundance of putative degraders belonging to Novosphingobium and Zoogloea. The chemical and microbiological results support (1) that simulation biodegradation kinetics should be determined in mixtures at low environmentally relevant concentrations and (2) that degradation times beyond some weeks are associated with more uncertainty.

Original languageEnglish
Pages (from-to)139-153
Number of pages15
Publication statusPublished - 2023

Bibliographical note

Funding Information: This study was funded by the company Global Product Compliance (GPC). The role of the sponsor was to provide a list of chemicals of interest to their industries from which the authors selected test chemicals. The sponsor was not involved in the study design, collection, analysis, and interpretation of data or writing of manuscript.


  • Xenobiotics
  • Simulation biodegradation
  • Microbial community
  • Passive dosing
  • 16S rRNA
  • Sequencing


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