So far, there is limited information on biotransformation mechanisms and products of polar contaminants in freshwater crustaceans. In the present study, metabolites of biocides and pharmaceuticals formed in Gammarus pulex and Daphnia magna were identified using liquid chromatography-high resolution mass spectrometry. Different confidence levels were assigned to the identification of metabolites without reference standards using a framework based on the background evidence used for structure elucidation. Twenty-five metabolites were tentatively identified for irgarol, terbutryn, tramadol, and venlafaxine in G. pulex (21 via oxidation and 4 via conjugation reactions) and 11 metabolites in D. magna (7 via oxidation and 4 via conjugation reactions), while no evidence of metabolites for clarithromycin and valsartan was found. Of the 360 metabolites predicted for the four parent compounds using pathway prediction systems and expert knowledge, 23 products were true positives, while 2 identified metabolites were unexpected products. Observed oxidative reactions included N- and O-demethylation, hydroxylation, and N-oxidation. Glutathione conjugation of selected biocides followed by subsequent reactions forming cysteine conjugates was described for the first time in freshwater invertebrates.

Exposure and depuration experiments for Gammarus pulex and Daphnia magna were conducted to quantitatively analyze biotransformation products (BTPs) of organic micropollutants (tramadol, irgarol, and terbutryn). Quantification for BTPs without available standards was performed using an estimation method based on physicochemical properties. Time-series of internal concentrations of micropollutants and BTPs were used to estimate the toxicokinetic rates describing uptake, elimination, and biotransformation processes. Bioaccumulation factors (BAF) for the parents and retention potential factors (RPF), representing the ratio of the internal amount of BTPs to the parent at steady state, were calculated. Nonlinear correlation of excretion rates with hydrophobicity indicates that BTPs with lower hydrophobicity are not always excreted faster than the parent compound. For irgarol, G.pulex showed comparable elimination, but greater uptake and BAF/RPF values than D.magna. Further, G. pulex had a whole set of secondary transformations that D. magna lacked. Tramadol was transformed more and faster than irgarol and there were large differences in toxicokinetic rates for the structurally similar compounds irgarol and terbutryn. Thus, predictability of toxicokinetics across species and compounds needs to consider biotransformation and may be more challenging than previously thought because we found large differences in closely related species and similar chemical structures.

No abstract

No abstract