From the exposome to mechanistic understanding of chemical-induced adverse effects.

The exposome encompasses an individual's exposure to exogenous chemicals, as well as endogenous chemicals that are produced or altered in response to external stressors. While the exposome concept has been established for human health, its principles can be extended to include broader ecological issues. The assessment of exposure is tightly interlinked with hazard assessment. Here, we explore if mechanistic understanding of the causal links between exposure and adverse effects on human health and the environment can be improved by integrating the exposome approach with the adverse outcome pathway (AOP) concept that structures and organizes the sequence of biological events from an initial molecular interaction of a chemical with a biological target to an adverse outcome. Complementing exposome research with the AOP concept may facilitate a mechanistic understanding of stress-induced adverse effects, examine the relative contributions from various components of the exposome, determine the primary risk drivers in complex mixtures, and promote an integrative assessment of chemical risks for both human and environmental health.

The German postgraduate degree program in ecotoxicology (SETAC GLB and GDCh): a success story.

This article gives a comprehensive overview on the strategy, the development and the progress of the German postgraduate degree program in ecotoxicology (SETAC GLB and GDCh). The program soon prompted positive results: more than 10 years now the courses had an average enrolment rate of 90 %, and employment-seeking graduates from the first courses mostly succeeded in quickly finding employment relevant to their training. With over 450 students enrolled to date, the degree program contributes significantly to the field of Environmental Chemistry and Ecotoxicology.

Semipolar polycyclic aromatic compounds: identification of 15 priority substances and the need for regulatory steps under REACH regulation.

Semipolar polycyclic aromatic compounds (sPACs) are frequently found in association with homocyclic polycyclic aromatic hydrocarbons (PAHs) in substances of unknown or variable composition, complex reaction products, or biological materials (UVCBs) from coal or crude oil and products derived thereof. However, major information deficiencies exist with regard to their prevalence and their toxicological and ecotoxicological potential, persistency, and bioaccumulation characteristics. Therefore, in this work, the environmental concern and relevance of sPACs was addressed in a general, stepwise approach. First, a large list of sPACs was collected and subsequently refined by assessing their persistence, bioaccumulation, and toxicity (PBT) properties by quantitative structure-activity relationship (QSAR) methods and their relevance by determining their respective frequency of occurrence. In this way, 15 priority sPACs were identified. These 15 priority sPACs were further characterized in detail with respect to their ecotoxicological properties, environmental behavior, carcinogenicity, and genotoxicity attributes. All of these 15 substances were quantified in distillate or product samples. In the next step, some principles for nomination of indicator substances, indicative for the overall content of sPACs, are derived. Data gaps on ecotoxicological endpoints preclude final conclusions, but the respective necessary supplemental tests were identified. Five of the 15 sPACs were tentatively characterized as potential substances of very high concern (SVHC) for the environment. The overall results of this study also clearly show that regulatory risk management of homocyclic PAHs within the European Regulation on Registration, Evaluation, Authorisation and Restriction of Chemicals (REACH) does not address the environmental concern created by sPACs within UVCBs from coal or crude oil. The study proves the need for additional regulatory steps under REACH and suggests indicator substances for their enforcement.

Quantitative assessment of the embryotoxic potential of NSO-heterocyclic compounds using zebrafish (Danio rerio).

Heterocyclic aromatic compounds (NSO-HET) have frequently been detected in the environment. Several studies have concluded that NSO-HET pose a threat to organisms in waters, sediments and soils. However, few publications are available assessing the ecotoxicology of NSO-HET. The present study aims to assess the embryo toxicity of heterocycles using Danio rerio. A combination of the Fish Embryo Toxicity Test and analytical quantification should aid to determine the hazard potential. Changes of the total concentrations due to sorption or volatility were quantified by GC/MS. Loss of compounds during the test was observed primarily for volatile or hydrophobic NSO-HET. The LC50 calculated with nominal concentrations underestimates the toxicity by a factor up to 16 (2 h), demonstrating that a chemical analysis for comparing nominal and measured concentrations is essential for such investigations.

Some heterocyclic aromatic compounds are Ah receptor agonists in the DR-CALUX assay and the EROD assay with RTL-W1 cells.

PURPOSE: Heterocyclic aromatic compounds containing nitrogen, sulfur, or oxygen heteroatoms (NSO-HET) have been detected in air, soil, marine, and freshwater systems. However, only few publications are available investigating NSO-HET using in vitro bioassays. To support better characterization of environmental samples, selected NSO-HET were screened for dioxin-like activity in two bioassays. METHODS: The present study focuses on the identification and quantification of dioxin-like effects of 12 NSO-HET using the DR-CALUX assay, and the 7-ethoxyresorufin-O-deethylase (EROD) assay with the permanent fish liver cell line RTL-W1. Changes of the total medium compound concentrations during the test procedure due to, e.g., sorption or volatilization were quantified using GC/MS. RESULTS: The NSO-HET benzofuran, 2,3-dimethylbenzofuran, dibenzofuran, dibenzothiophen, acridine, xanthene, and carbazole caused a response in the DR-CALUX assay. Only benzofuran and 2,3-dimethylbenzofuran were also positive in the EROD assay. All other compounds were inactive in the EROD assay. Relative potency (REP) values ranged from (2.80 ± 1.32) · 10(-8) to (3.26 ± 2.03) · 10(-6) in the DR-CALUX and from (3.26 ± 0.91) · 10(-7) to (4.87 ± 1.97) · 10(-7) in the EROD assay. CONCLUSIONS: The REP values were comparable to those of larger polycyclic aromatic hydrocarbons, e.g., fluoranthene and pyrene. Thus, and because of the ubiquitous distribution of heterocyclic aromatic compounds in the environment, the provided data will further facilitate the bioanalytical and analytical characterization of environmental samples towards these toxicants.

Proposing a pH stabilised nutrient medium for algal growth bioassays.

Ecotoxicological assessment of chemicals and contaminated sites relies on bioassays using apical endpoints such as detection of growth inhibition using suspension cultures of green algae. For valid effect assessment observable responses should be causally linked to chemical exposure and thus confounding factors should be minimised. In this study we report that concentration response relationships for substances in current standardised protocols for unicellular algal growth assays are prone to variation from ill-defined assay conditions. The currently used growth media are not optimised to provide a stable pH regime for an exposure period of 72h, resulting in undefined speciation for charged or ionising molecules. We therefore propose a modified pH-stabilised growth medium for algal bioassays and demonstrate that this can substantially reduce variation in effect determination for reference compounds.