Suchergebnisse

AbstractBioconcentration tests using the freshwater amphipod Hyalella azteca as an alternative to conventional fish tests have recently received much attention. An appropriate computational model of H. azteca could help in understanding the mechanisms behind bioconcentration, in comparison to the fish as test organism. We here present the first mechanistic model for H. azteca that considers the single diffusive processes in the gills and gut. The model matches with the experimental data from the literature quite well when appropriate physiological information is used. The implementation of facilitated transport was essential for modeling. Application of the model for superhydrophobic compounds revealed binding to organic matter and the resulting decrease in bioavailable fraction as the main reason for the observed counterintuitive decrease in uptake rate constants with increasing octanol/water partition coefficient. Furthermore, estimations of the time needed to reach steady state indicated that durations of more than a month could be needed for compounds with a log Kow > 8, limiting the experimental applicability of the test. In those cases, model-based bioconcentration predictions could be a preferable approach, which could be combined with in vitro biotransformation measurements. However, our sensitivity analysis showed that the uncertainty in determining the octanol/water partition coefficients is a strong source of error for superhydrophobic compounds.

Bioconcentration tests with the freshwater amphipod Hyalella azteca (HYBIT) have been proposed as alternatives to fish tests, and the respective experimental BCF values show promising correlations. It is unclear whether the HYBIT test is also suitable for highly hydrophobic chemicals, such as UV stabilizers UV-234 and UV-329. In order to estimate the range in which the uptake rate constant k1 would be expected for these substances, a prediction method for k1 in H. azteca was developed in this work. As a result, we found that the experimental literature values appear plausible compared to the predicted values within the given uncertainties, however, more experimental data is needed for a conclusive validation. The main uncertainties for the prediction are the uncertainty of the determination of the octanol/water partition coefficient and the chemical's binding to organic matter in water (TOC). Compared to fish tests, HYBIT seems promising for superhydrophobic substances, not only because of the experimental advantages such as smaller experimental units. According to the model, measurement (in the absence of metabolism) will benefit from a tendencially higher depuration rate constant k2 in H. azteca than in fish, which would shorten the time to steady state. Nevertheless, for H. azteca, according to the modeling, the required times till steady state in the superhydrophobic range are to be expected far longer than standard test durations (up to months). However, the use of the BCF as an evaluation criterion for the bioaccumulation of superhydrophobic substances is conceptually questionable. For superhydrophobic substances, the introduction of feces as an additional elimination path, without the parallel intake of contaminated food as would be realistic, has the effect that even without metabolism or growth, the BCF values decrease with increasing Kow, which would not be expected under real circumstances.

Das Ziel der vorliegenden Studie war es, die Bioakkumulation vollständig ionisierter Verbindungen experimentell zu bestimmen und Screening-Parameter zu identifizieren, die auf ein hohes Bioakkumulationspotential von ionisierbaren organischen Chemikalien (IOCs) hinweisen können. Drei Fütterungsstudien mit Regenbogenforellen (Oncorhynchus mykiss) wurden gemäß OECD TG 305 durchgeführt. Die Trennung von Leber, Magen-Darm-Trakt (GIT) und Schlachtkörper ermöglichte eine weitere Aufklärung der Gewebeverteilung der einzelnen Testsubstanzen. Die ausgewählten Chemikalien wiesen Eigenschaften auf, die sie für eine hohe Bioakkumulation verdächtig machten, und umfassten zwei Kationen (Tetrabutylphosphoniumbromid (TBP), Trimethyloctadecylammoniumchlorid (TMOA)) und vier Anionen (Benzotriazol, Tecloftalam, Pentachlorphenol (PCP), MEE-Phosphonat). Die höchsten Verteilungsfaktoren wurden für die GIT gefunden, gefolgt von der Leber. Keine der getesteten IOCs zeigte jedoch ein ausgeprägtes Biomagnifikationspotential, da die kinetischen Biomagnifikationsfaktoren (BMFk) zwischen 0,001 und 0,05 g / g lagen (Median 0,009 g / g). Die getesteten Kationen zeigten mit Ausnahme von Tecloftalam eine geringere Assimilationseffizienz (α) (siehe OECD TG 305) als die Anionen. Im Gegensatz dazu zeigten die getesteten Anionen eine erheblich schnellere Depurationsrate (Halbwertszeit weniger als 0,5 Tage) als die Kationen (Halbwertszeit von etwa 5 Tagen). Zwanzig mögliche Screening-Parameter für das Biomagnifikationspotential ionisierter Verbindungen wurden mit verfügbaren Schätzwerkzeugen (ACD / i-Lab und COSMOmic) berechnet und mit BMF-Daten aus dieser Studie und aus der Literatur korreliert. Der COSMOmic KFisch / Wasser zeigte die höchste Korrelation zum gemessenen BMF, während die meisten anderen Deskriptoren nicht signifikant korrelierten. Das vermutete Bioakkumulationspotential der sechs IOC nach Aufnahme über die Nahrung konnte in den Fütterungsstudien mit Regenbogenforellen nicht bestätigt werden. Keiner der mehr als zwanzig Screening-Parameter zeigte eine besonders hohe Korrelation mit den Testergebnissen oder den aus der Literatur gesammelten BMF-Werten. Insgesamt kann aus dem Screening geschlossen werden, dass die Ionisierung einer Chemikalie die Tendenz zur Bioakkumulation im Vergleich zu nichtionisierten Chemikalien verringert. Eine schnelle Depuration scheint ein Hauptgrund für die beobachtete geringe Biomagnifikation ionischer Verbindungen, insbesondere der Anionen, zu sein. Aufgrund des schnellen Metabolismus oder der Konjugation geladener Verbindungen kann es zu einer schnellen Depuration kommen. Zukünftige Studien sollten diese Hypothese überprüfen.

The aim of the project was a review of the current version of the concept to identify persistent, bioaccumulative and toxic (PBT) and very persistent and very bioaccumulative (vPvB) substances under the EU regulation (EC) No. 1907/2006 concerning the Registration, Evaluation, Authorisation and Restriction of Chemicals (REACH), hereafter referred to as "PBT concept". The German Environment Agency (UBA) contracted Oeko-Institut, ETH Zürich and BiPRO to review the current PBT concept and to propose updates and adjustments. The project was designated to support UBA in its active contribution to the identification of new PBT substances. In a first step, an evaluation of a number of already existing PBT/vPvB classifications was conducted, 57 of which were classified as non-PBT substances with a strong indication that 8 substances might be PBT substances. For the assessment of environmental monitoring data, substances detected in remote areas were compiled and examined based on EpiSuite estimations for their P and B properties. In order to further strengthen the PBT concept two main steps were carried out: a review of the PBT/vPvB concept as implemented under REACH, and the implementation of the concept with the aim to identify substances of very high concern, and proposals for updating the PBT concept by developing suggestions on how to overcome the major challenges. Proposals for amendments or adjustments of PBT concept were discussed on a workshop with international PBT experts in June 2017.