How Biotransformation Influences Toxicokinetics of Azole Fungicides in the Aquatic Invertebrate Gammarus pulex

Abstract

Biotransformation is a key process that can greatly influence the bioaccumulation potential and toxicity of organic compounds. In this study, biotransformation of seven frequently used azole fungicides (triazoles: cyproconazole, epoxiconazole, fluconazole, propiconazole, tebuconazole and imidazoles: ketoconazole, prochloraz) was investigated in the aquatic invertebrate Gammarus pulex in a 24 h exposure experiment. Additionally, temporal trends of the whole body internal concentrations of epoxiconazole, prochloraz, and their respective biotransformation products (BTPs) were studied to gain insight into toxicokinetic processes such as uptake, elimination and biotransformation. By the use of high resolution tandem mass spectrometry in total 37 BTPs were identified. Between one (ketoconazole) and six (epoxiconazole) BTPs were identified per parent compound except for prochloraz, which showed extensive biotransformation reactions with 18 BTPs detected that were mainly formed through ring cleavage or ring loss. In general, most BTPs were formed by oxidation and conjugation reactions. Ring loss or ring cleavage was only observed for the imidazoles as expected from the general mechanism of oxidative ring openings of imidazoles, likely affecting the bioactivity of these BTPs. Overall, internal concentrations of BTPs were up to 3 orders of magnitude lower than that of the corresponding parent compound. Thus, biotransformation did not dominate toxicokinetics and only played a minor role in elimination of the respective parent compound, with the exception of prochloraz.

Uptake, biotransformation and elimination of selected pharmaceuticals in a freshwater invertebrate measured using liquid chromatography tandem mass spectrometry

“…As the data suggests, factors other than hydrophobicity may be important in accumulation, such as biotransformation, which could also partly explain the variability in BCFs. Authors have demonstrated that G. pulex are able to metabolise a range of organic micropollutants (Ashauer et al., 2012, Jeon et al., 2013b, Rösch et al., 2016). Conservation of cytochrome P450 enzymes has also been observed in invertebrates (Snyder, 2000) and pharmaceuticals have been shown to undergo oxidative and conjugation reactions (Jeon et al., 2013b).…”

“…For biocides (algicides), glutathione conjugates have been detected in G. pulex and D. magna (Jeon et al., 2013b). Finally, G. pulex have also been shown to biotransform azole fungicides into sulphate, glutathione and glucose-sulphate conjugates (Rösch et al., 2016). Human trials show that the major biotransformation products of propranolol were HP and napthoxylactic acid (Walle and Gaffney, 1972).…”

“…Therefore, untargeted analytical techniques such as high resolution mass spectrometry (HRMS) could potentially offer a much greater insight into biotransformation pathways involved with xenobiotic detoxification or identification of new compounds (Ashauer et al., 2012, Munro et al., 2015). However, the quantitative application of LC-HRMS to toxicokinetic profiling needs to be considered carefully, especially where reference materials for biotransformation products are not available as discussed previously (Jeon et al., 2013a, Rösch et al., 2016). Furthermore, studies that only monitor the parent compound by non-specific methods should be cautious when reporting BCFs, especially if there is a high potential for biotransformation.…”

“…To date only three studies have measured biotransformation products and their associated toxicokinetics in invertebrates (Ashauer et al., 2012, Jeon et al., 2013b, Rösch et al., 2016). Two of these works used LC coupled to high resolution MS (HRMS) or LC with a radioactivity detector to model the uptake and elimination profiles of organic micropollutants and their biotransformation products in G. pulex (Ashauer et al., 2012, Rösch et al., 2016).…”

“…Two of these works used LC coupled to high resolution MS (HRMS) or LC with a radioactivity detector to model the uptake and elimination profiles of organic micropollutants and their biotransformation products in G. pulex (Ashauer et al., 2012, Rösch et al., 2016). Ashauer et al.…”