Four selected high molecular weight heterocyclic aromatic hydrocarbons: Ecotoxicological hazard assessment, environmental relevance and regulatory needs under REACH

Abstract

Little is known about the ecotoxicity of heterocyclic aromatic hydrocarbons (NSO-HETs) to aquatic organisms. In the environment, NSO-HETs have been shown to occur in a strong association with their unsubstituted carbocyclic analogues, the polycyclic aromatic hydrocarbons (PAH), for which much more information is available. The present study addressed this issue by investigating the toxicity of four selected NSO-HETs in green algae (Desmodesmus subspicatus), daphnids (Daphnia magna) and fish embryos (Danio rerio). The four high molecular weight NSO-HETs dibenz[a,j]acridine (DBA), 7H-dibenzo[c,g]carbazole (DBC), benzo[b]naphtho[2,1-d]thiophene (BNT) and benzo[b]naphtho[1,2-d]furan (BNF) were selected, based on the results of a previous research project, indicating a lack of toxicity data and a high potential for persistence and bioaccumulation. The solubilities of the NSO-HETs in the test media were determined and turned out to be comparatively low (2.7-317 µg/L) increasing in the following order: DBA < BNT « DBC « BNF. Exposure concentrations during the toxicity tests were quantified with GC-MS and decreased strongly possibly due to sorption or metabolising during the test periods (48-96 h). Therefore, the estimated effect concentrations were related to the mean measured concentrations, as endpoints related to nominal concentrations would have underestimated the toxicity many times over. Within the range of the substance solubilities, BNF affected all test organisms with fish embryos being the most sensitive (fish: EC 6.7 µg/L, algae: EC 17.8 µg/L, daphnids: EC 55.8 µg/L). DBC affected daphnids (EC 2.5 µg/L,) and algae (EC 3.1 µg/L), but not fish embryos. The lowest toxicity endpoint was observed for BNT affecting only algae (NOEC 0.556 µg/L) and neither daphnids nor fish embryos. DBA did not show any effects on the tested organisms in the range of the water solubility. However, we would expect effects in long-term toxicity studies to fish and aquatic invertebrates for all substances at lower concentrations, which needs further investigation. All four NSO-HETs were identified in mussels (Mytilus edulis) from the German coasts, in green kale (Brassica oleracea var. acephala) and in freshwater harbor sediment in concentrations between 0.07 and 2 µg/kg, highlighting their relevance as environmental contaminants. There is a need to regulate the four NSO-HETs within the REACH regulation due to their intrinsic properties and their environmental relevance. However, acquisition of additional experimental data appears to be pivotal for a regulation under REACH.

Environmental Hazard Screening of Heterocyclic Polyaromatic Hydrocarbons: Physicochemical Data and In Silico Models

“…41,42 The aqueous solubility of BNF (0.25 ± 0.01 mg L −1 ) was also consistent with a literature value where the solubility of BNF was determined at 20 °C in Elendt M4 medium (described in OECD guideline 202) containing some inorganic salts (0.25 mg L −1 ). 43 The equilibrium kinetics of the measured S w are shown in Figure S1.…”

Application of the Target Lipid Model to Assess Toxicity of Heterocyclic Aromatic Compounds to Aquatic Organisms

“…One data point was a C. dubia reproduction EC10 value of 1.16 µg/L (0.007 µmol/L) for 2‐hexylthiophene (ExxonMobil Biomedical Sciences [EMBSI], 2020a ). The other data point was a D. subspicatus growth rate NOEC value of 0.566 µg/L (0.002 µmol/L) for benzo[ b ]naphtha [2,1‐d]thiophene (Brendal et al, 2018 ). The excursion of 2 out of 37 data points below the HC5 is consistent with the 95% protection level goal (i.e., 94.6% [35/37]).…”

“…The HACs are more polar and subsequently more soluble than their homocyclic counterparts and can be bioavailable in environmental media. These compounds have been measured in a variety of environmental matrices, and studies have reported effects on aquatic organisms (Bleeker et al, 1998 ; Brendel et al, 2018 ; Dijkman et al, 1997 ; Peddinghaus et al, 2012 ). Presumably, due to their lower concentrations in the environmental in comparison with their homocyclic counterparts, these heterocyclic polycyclic aromatic compounds (PACs) are not considered to be risk drivers.…”

“…Presumably, due to their lower concentrations in the environmental in comparison with their homocyclic counterparts, these heterocyclic polycyclic aromatic compounds (PACs) are not considered to be risk drivers. However, recent literature on risk assessments of PACs indicates there is a need to include the heterocylic compounds in a risk assessment framework (Brendel et al, 2018 ; Hodson et al, 2020 ; Schwarz et al, 2014 ). The present study provides the hazard framework to evaluate the validity of this assumption and the need to develop a mechanistic based approach to characterize the toxicity of the heterocyclic PACs.…”

Aquatic plants and ecotoxicological assessment in freshwater ecosystems: a review

“…In natural conditions, however, in presence of relevant solar radiation, a number of PAHs were found to be acutely toxic to aquatic organisms at concentrations that were similar to those tested in laboratory (Landrum et al 1984;Oris et al 1984), thus highlighting the importance of carrying out toxicological analyses in experimental conditions that are as similar as possible to those found in field. Also, the knowledge on ecotoxicity of NSO-HETs to aquatic plants is still rather scarce (Brendel et al 2018).…”