No abstract

In the present study, relative potency factors (REPs) of 16 individual polycyclic aromatic hydrocarbons (PAHs) were investigated using the H4IIE-luc bioassay. Exposure time-dependent effects on the REPs were examined using 24, 48, and 72 h of exposure. Seven different mixtures of PAHs were tested for additivity at an exposure time of 24 h. Three of the PAH mixtures were also studied at 48 and 72 h of exposure. The mixture toxicities were predicted using the REP concept and the concentration addition (CA) model. Relative potency factor values investigated in the present study were similar to those reported in earlier studies. Declining REPs with an increasing exposure time were shown for all PAHs, indicating that this bioassay approach could be developed to assess the persistency of aryl hydrocarbon receptor (AhR) agonistic PAHs and in the risk assessment of complex PAH mixtures. The results from the mixture studies indicated that additive interactions of PAHs are time dependent. Generally, 48- and 72-h exposures resulted in biological effects that were similar to the CA and REP model predictions, while these models tended to underestimate the effect, to some extent, in the 24-h exposure, at least for the mixtures containing two to four PAHs. Thus, it cannot be ruled out that in the 24-h exposures, the tested PAH mixtures had slight synergistic effects. Further research is needed to identify and test additional AhR activating PAHs and investigate whether the effects in the H4IIE-luc bioassay are additive for more complex samples containing both PAHs and other AhR-activating contaminants. Also, the observed superinduction of luciferase by PAH-mixes warrants studies of whether this also can occur for relevant AhR-mediated endpoints in vivo.

Twenty-six polycyclic aromatic compounds (PACs; including native polycyclic aromatic hydrocarbons [PAHs], hydroxylated PAHs, alkylated and oxygenated PAHs, and [alkylated] heterocyclic compounds) were investigated for their aryl hydrocarbon receptor (AhR)-mediated potencies in the H4IIE-luc bioassay. Potential degradabilities of PACs were investigated by use of various durations of exposure (24, 48, or 72 h), and various mixtures of PACs including PAHs, alkylated and oxygenated PAHs, and heterocyclic compounds were tested for their joint AhR-mediated potency. Additive behaviors of PACs in mixtures were studied by comparing observed mixture potencies with mixture potencies predicted by use of the concentration addition model. Methylated derivatives were more potent than their parent compounds in the H4IIE-luc assay. A time-dependent decrease in relative potency was observed for all AhR-active compounds, which may be indicative of in vitro biotransformation. Monomethylated compounds seemed to be more rapidly transformed than analogous unsubstituted compounds. In addition, the results showed that the predictive power of the concentration addition model increased with the number of compounds, suggesting additivity in multicomponent mixtures. Due to the greater potency of methylated derivatives and their ubiquitous occurrence, there is a need for further research on the toxicity and mixture behavior of these environmentally and toxicologically relevant compounds. Environ Toxicol Chem 2018;37:1409-1419. © 2018 SETAC.

No abstract

Polycyclic aromatic hydrocarbons (PAHs) are common contaminants in soil at former industrial areas; and in Sweden, some of the most contaminated sites are being remediated. Generic guideline values for soil use after so-called successful remediation actions of PAH-contaminated soil are based on the 16 EPA priority pollutants, which only constitute a small part of the complex cocktail of toxicants in many contaminated soils. The aim of the study was to elucidate if the actual toxicological risks of soil samples from successful remediation projects could be reflected by chemical determination of these PAHs. We compared chemical analysis (GC-MS) and bioassay analysis (H4IIE-luc) of a number of remediated PAH-contaminated soils. The H4IIE-luc bioassay is an aryl hydrocarbon (Ah) receptor-based assay that detects compounds that activate the Ah receptor, one important mechanism for PAH toxicity. Comparison of the results showed that the bioassay-determined toxicity in the remediated soil samples could only be explained to a minor extent by the concentrations of the 16 priority PAHs. The current risk assessment method for PAH-contaminated soil in use in Sweden along with other countries, based on chemical analysis of selected PAHs, is missing toxicologically relevant PAHs and other similar substances. It is therefore reasonable to include bioassays in risk assessment and in the classification of remediated PAH-contaminated soils. This could minimise environmental and human health risks and enable greater safety in subsequent reuse of remediated soils.