Département Chimie de l’environnement

Bioakkumulations- und Biotransformationsprozesse polarer organischer Schadstoffe in aquatischen Invertebraten - Die Verknüpfung von Exposition und Effekten

(Foto: Eawag)
Der gewöhnliche Flohkrebs, Gammarus pulex, beim Zerkleinern von Falllaub. (Foto: Eawag)


Monitoring-Studien mit aquatischen Invertebraten zeigen, dass die Gewebekonzentrationen vieler Schadstoffe wesentlich höher sind als anhand von Modellen, basierend auf Laborstudien und gemessenen Wasserkonzentrationen, vorhergesagt. Dies ist insbesondere bei (semi-) polaren Verbindungen, einschließlich Pharmazeutika und systemischer Pestizide der Fall. Solche Abweichungen können zu Unterschätzungen in der Umweltrisikobewertung führen, da letztendlich interne Konzentrationen die Ursache für toxikologische Effekte sind. Das Verständnis toxikokinetischer Prozesse ist daher unerlässlich, um die Übertragbarkeit von Labordaten auf die Umwelt zu verbessern und Exposition sowie Effekt mechanistisch miteinander zu verknüpfen.

Dieses Projekt zielt auf die Aufklärung von Bioakkumulations- und Biotransformationsprozessen sowie Parametern ab, die möglicherweise für die beobachtete Diskrepanz verantwortlich sind und in die Modelle aufgenommen werden könnten. Die Untersuchungen werden mit den beiden Süßwasseramphipoden Gammarus pulex (Europa) und Hyalella azteca (Nordamerika) durchgeführt und umfassen folgende toxikokinetische Prozesse:
 

  • Aufnahmepfad Nahrung
    Bioakkumulations- sowie Sorptions- und Auslaugungsexperimente werden mit Laub              durchgeführt, das von mit systemischen Pestiziden exponierten Bäumen stammmt (Zusammenarbeit mit der Universität Koblenz-Landau )
     
  • Räumliche Verteilung
    In Zusammenarbeit mit der Universität Kopenhagen wird die Methode der bildgebenden Massenspektrometrie verwendet, um den Zugang zu molekularen Wirkorten und die Senken von angereicherten Schadstoffen zu bestimmen
     
  • Temperatur
    In Mikrokosmenstudien quantifizieren wir den Einfluss von Temperatur - ein wesentlicher Antrieb chemischer und biologischer Prozesse - auf die Toxikokonetik von Schadstoffen
     

  • Rezeptor Bindung
    Eine Kombination aus toxikokinetischen Experimenten und Rezeptorbindungsassays wird angewendet, um Multi-Kompartiment toxikokinetische und toxikodynamische Modellierung zu ermöglichen. Ausserdem haben wir die Rezeptorbindung als Ursache für Kontaminationsrückstände identifiziert, die gegenüber der Eliminierung aus Geweben resistent sind.
     

  • Aktiver Transport
    Die aktiven Aufnahme- und Eliminationsprozesse kationischer psychoaktiver Medikamente mit Hilfe von Transporter-Inhibitor-Assays aufgeklärt.

Publikationen

Elimination resistance: characterizing multi-compartment toxicokinetics of the neonicotinoid thiacloprid in the amphipod Gammarus pulex using bioconcentration and receptor-binding assays

Delayed toxicity is a phenomenon observed for aquatic invertebrates exposed to nicotinic acetylcholine receptor (nAChR) agonists, such as neonicotinoids. Furthermore, recent studies have described an incomplete elimination of neonicotinoids by exposed amphipods. However, a mechanistic link between receptor binding and toxicokinetic modeling has not been demonstrated yet. The elimination of the neonicotinoid thiacloprid in the freshwater amphipod Gammarus pulex was studied in several toxicokinetic exposure experiments, complemented with in vitro and in vivo receptor-binding assays. Based on the results, a two-compartment model was developed to predict the uptake and elimination kinetics of thiacloprid in G. pulex. An incomplete elimination of thiacloprid, independent of elimination phase duration, exposure concentrations, and pulses, was observed. Additionally, the receptor-binding assays indicated irreversible binding of thiacloprid to the nAChRs. Accordingly, a toxicokinetic-receptor model consisting of a structural and a membrane protein (including nAChRs) compartment was developed. The model successfully predicted internal thiacloprid concentrations across various experiments. Our results help in understanding the delayed toxic and receptor-mediated effects toward arthropods caused by neonicotinoids. Furthermore, the results suggest that more awareness toward long-term toxic effects of irreversible receptor binding is needed in a regulatory context. The developed model supports the future toxicokinetic assessment of receptor-binding contaminants.
Raths, J.; Schinz, L.; Mangold-Döring, A.; Hollender, J. (2023) Elimination resistance: characterizing multi-compartment toxicokinetics of the neonicotinoid thiacloprid in the amphipod Gammarus pulex using bioconcentration and receptor-binding assays, Environmental Science and Technology, 57(24), 8890-8901, doi:10.1021/acs.est.3c01891, Institutional Repository

Speed it up: how temperature drives toxicokinetics of organic contaminants in freshwater amphipods

The acceleration of global climate change draws increasing attention towards interactive effects of temperature and organic contaminants. Many studies reported a higher sensitivity of aquatic invertebrates towards contaminant exposure with increasing or fluctuating temperatures. The hypothesis of this study was that the higher sensitivity of invertebrates is associated with the changes of toxicokinetic processes that determine internal concentrations of contaminants and consequently toxic effects. Therefore, the influence of temperature on toxicokinetic processes and the underlying mechanisms were studied in two key amphipod species (Gammarus pulex and Hyalella azteca). Bioconcentration experiments were carried out at four different temperatures with a mixture of 12 exposure relevant polar organic contaminants. Tissue and medium samples were taken in regular intervals and analysed by online solid-phase extraction liquid chromatography high-resolution tandem mass spectrometry. Subsequently, toxicokinetic rates were modelled and analysed in dependence of the exposure temperature using the Arrhenius equation. An exponential relationship between toxicokinetic rates versus temperature was observed and could be well depicted by applying the Arrhenius equation. Due to a similar Arrhenius temperature of uptake and elimination rates, the bioconcentration factors of the contaminants were generally constant across the temperature range. Furthermore, the Arrhenius temperature of the toxicokinetic rates and respiration was mostly similar. However, in some cases (citalopram, cyprodinil), the bioconcentration factor appeared to be temperature dependent, which could potentially be explained by the influence of temperature on active uptake mechanisms or biotransformation. The observed temperature effects on toxicokinetics may be particularly relevant in non-equilibrated systems, such as exposure peaks in summer as exemplified by the exposure modelling of a field measured pesticide peak where the internal concentrations increased by up to fourfold along the temperature gradient. The results provide novel insights into the mechanisms of chemical uptake, biotransformation and elimination in different climate scenarios and can improve environmental risk assessment.
Raths, J.; Švara, V.; Lauper, B.; Fu, Q.; Hollender, J. (2023) Speed it up: how temperature drives toxicokinetics of organic contaminants in freshwater amphipods, Global Change Biology, 29(5), 1390-1406, doi:10.1111/gcb.16542, Institutional Repository

Importance of dietary uptake for in situ bioaccumulation of systemic fungicides using Gammarus pulex as a model organism

Bioaccumulation of organic contaminants from contaminated food sources might pose an underestimated risk toward shredding invertebrates. This assumption is substantiated by monitoring studies observing discrepancies of predicted tissue concentrations determined from laboratory-based experiments compared with measured concentrations of systemic pesticides in gammarids. To elucidate the role of dietary uptake in bioaccumulation, gammarids were exposed to leaf material from trees treated with a systemic fungicide mixture (azoxystrobin, cyprodinil, fluopyram, and tebuconazole), simulating leaves entering surface waters in autumn. Leaf concentrations, spatial distribution, and leaching behavior of fungicides were characterized using liquid chromatography coupled with high-resolution tandem mass spectrometry (LC-HRMS/MS) and matrix-assisted laser desorption ionization-mass spectrometric imaging. The contribution of leached fungicides and fungicides taken up from feeding was assessed by assembling caged (no access) and uncaged (access to leaves) gammarids. The fungicide dynamics in the test system were analyzed using LC-HRMS/MS and toxicokinetic modeling. In addition, a summer scenario was simulated where water was the initial source of contamination and leaves contaminated by sorption. The uptake, translocation, and biotransformation of systemic fungicides by trees were compound-dependent. Internal fungicide concentrations of gammarids with access to leaves were much higher than in caged gammarids of the autumn scenario, but the difference was minimal in the summer scenario. In food choice and dissectioning experiments gammarids did not avoid contaminated leaves and efficiently assimilated contaminants from leaves, indicating the relevance of this exposure pathway in the field. The present study demonstrates the potential impact of dietary uptake on in situ bioaccumulation for shredders in autumn, outside the main application period. The toxicokinetic parameters obtained facilitate modeling of environmental exposure scenarios. The uncovered significance of dietary uptake for detritivores warrants further consideration from scientific as well as regulatory perspectives.
Raths, J.; Schnurr, J.; Bundschuh, M.; Pinto, F. E.; Janfelt, C.; Hollender, J. (2023) Importance of dietary uptake for in situ bioaccumulation of systemic fungicides using Gammarus pulex as a model organism, Environmental Toxicology and Chemistry, 42(9), 1993-2006, doi:10.1002/etc.5615, Institutional Repository

Elucidating the spatial distribution of organic contaminants and their biotransformation products in amphipod tissue by MALDI- and DESI-MS-imaging

The application of mass spectrometry imaging (MSI) is a promising tool to analyze the spatial distribution of organic contaminants in organisms and thereby improve the understanding of toxicokinetic and toxicodynamic processes. MSI is a common method in medical research but has been rarely applied in environmental science. In the present study, the suitability of MSI to assess the spatial distribution of organic contaminants and their biotransformation products (BTPs) in the aquatic invertebrate key species Gammarus pulex was studied. Gammarids were exposed to a mixture of common organic contaminants (carbamazepine, citalopram, cyprodinil, efavirenz, fluopyram and terbutryn). The distribution of the parent compounds and their BTPs in the organisms was analyzed by two MSI methods (MALDI- and DESI-HRMSI) after cryo-sectioning, and by LC-HRMS/MS after dissection into different organ compartments. The spatial distribution of contaminats in gammarid tissue could be successfully analyzed by the different analytical methods. The intestinal system was identified as the main site of biotransformation, possibly due to the presence of biotransforming enzymes. LC-HRMS/MS was more sensitive and provided higher confidence in BTP identification due to chromatographic separation and MS/MS. DESI was found to be the more sensitive MSI method for the analyzed contaminants, whereas additional biomarkers were found using MALDI. The results demonstrate the suitability of MSI for investigations on the spatial distribution of accumulated organic contaminants. However, both MSI methods required high exposure concentrations. Further improvements of ionization methods would be needed to address environmentally relevant concentrations.
Raths, J.; Pinto, F. E.; Janfelt, C.; Hollender, J. (2023) Elucidating the spatial distribution of organic contaminants and their biotransformation products in amphipod tissue by MALDI- and DESI-MS-imaging, Ecotoxicology and Environmental Safety, 264, 115468 (10 pp.), doi:10.1016/j.ecoenv.2023.115468, Institutional Repository

Systematic underestimation of pesticide burden for invertebrates under field conditions: comparing the influence of dietary uptake and aquatic exposure dynamics

Pesticides used in agriculture can end up in nearby streams and can have a negative impact on nontarget organisms such as aquatic invertebrates. During registration, bioaccumulation potential is often investigated using laboratory tests only. Recent studies showed that the magnitude of bioaccumulation in the field substantially differs from laboratory conditions. To investigate this discrepancy, we conducted a field bioaccumulation study in a stream known to receive pollutant loadings from agriculture. Our work incorporates measurements of stream pesticide concentrations at high temporal resolution (every 20 min), as well as sediment, leaves, and caged gammarid analyses (every 2-24 h) over several weeks. Of 49 investigated pesticides, 14 were detected in gammarids with highly variable concentrations of up to 140 ± 28 ng/gww. Toxicokinetic modeling using laboratory-derived uptake and depuration rate constants for azoxystrobin, cyprodinil, and fluopyram showed that despite the highly resolved water concentrations measured, the pesticide burden on gammarids remains underestimated by a factor of 1.9 ± 0.1 to 31 ± 3.0, with the highest underestimations occurring after rain events. Including dietary uptake from polluted detritus leaves and sediment in the model explained this underestimation only to a minor proportion. However, suspended solids analyzed during rain events had high pesticide concentrations, and uptake from them could partially explain the underestimation after rain events. Additional comparison between the measured and modeled data showed that the pesticide depuration in gammarids is slower in the field. This observation suggests that several unknown mechanisms may play a role, including lowered enzyme expression and mixture effects. Thus, it is important to conduct such retrospective risk assessments based on field investigations and adapt the registration accordingly.
Lauper, B. B.; Anthamatten, E.; Raths, J.; Arlos, M.; Hollender, J. (2022) Systematic underestimation of pesticide burden for invertebrates under field conditions: comparing the influence of dietary uptake and aquatic exposure dynamics, ACS Environmental Au, 2(2), 166-175, doi:10.1021/acsenvironau.1c00023, Institutional Repository