Effect-Directed Assessment of the Bioaccumulation Potential and Chemical Nature of AhReceptor Agonists in Crude and Refined Oils.

Abstract

Recent studies have indicated that in addition to narcosis certain chemicals in crude oils and refined petroleum products may induce specific modes of action, such as aryl hydrocarbon receptor (AhR) agonism. The risks these toxic compounds pose to organisms depend on internal exposure levels, as driven by the chemicals' bioaccumulation potential. Information on this potential however is lacking, as the chemicals' identity mostly is unknown. This study showed that AhR agonists bioaccumulate from oil-spiked sediments into aquatic worms and persist in the worms for at least several weeks. Chemical fractionations of eight pure oils into saturates, aromatics, resins, and asphaltenes (SARA), followed by effect-directed analyses using in vitro reporter gene assays revealed that the agonists predominantly are aromatic and resin-like chemicals. Some of the compounds were easily metabolized in vitro, while others were resistant to biotransformation. HPLC-assisted hydrophobicity profiling subsequently indicated that the AhR-active chemicals had a high to extremely high bioaccumulation potential, considering their estimated logK(ow) values of 4 to >10. Most of the AhR agonism, however, was assigned to compounds with logK(ow) of 5-8. These compounds were present mainly in the mid to high boiling point fractions of the oils (C(14)-C(32) alkane range), which are usually not being considered (the most) toxic in current risk assessment. The fractionations further revealed considerable oil and fraction-dependent antagonism in pure oils and SARA fractions. The results of this study clearly demonstrate that crude oils and refined petroleum products contain numerous compounds that can activate the AhR and which because of their likely persistence and extremely high bioaccumulation potential could be potential PBT (persistent, bioaccumulative and toxic) or vPvB (very persistent and very bioaccumulative) substance candidates. Many chemicals were identified by GC-MS, but the responsible individual compounds could not be exactly identified in the complex mixtures of thousands of compounds. Because this obstructs a classical PBT risk assessment, our results advocate an adapted risk assessment approach for complex mixtures in which low concentrations of very potent compounds are responsible for mixture effects.

Characterization of AhR agonist compounds in roadside snow

“…4), which made nontarget screening impossible using conventional GC since individual compounds could not be resolved. This UCM may contain a high proportion of aromatic AhR agonists, which is supported by recent work that has shown that the largely unresolved aromatic fraction isolated from crude oil is a potent inducer of the AhR [31]. In another study, the produced UCM has been lethal to benthic organisms at environmentally relevant concentrations, and it was shown to enhance the bioavailability of PAHs by competing for sorption to TOC [32].…”

Effect-directed analysis and mixture effects of AhR-active PAHs in crude oil and coastal sediments contaminated by the Hebei Spirit oil spill

“…Among the six sub-fractions of F2, significantly greater AhRmediated potencies were found in the F2.2 and F2.3 containing 3 to 4 rings of aromatics and/or aromatics of similar molar mass (166e234) in crude oil (Table S4). The further identification of specific AhR agonist(s), targeting sub-fractions of F2.2 and F2.3 in crude oil and/or sedimentary residual oils, would be necessary to narrow down possible causative chemicals to individual compound(s) (Vrabie et al, 2012).…”

“…Effect-directed analysis (EDA) has become a powerful tool for identification of major toxicant(s) that occur in complex mixtures in the environment encompassing composites of sediments, soil, and effluents (Brack et al, 2002;Regueiro et al, 2013;Vrabie et al, 2012). The separated fractions contain successively fewer groups or individual organic chemicals of similar functionality or polarity, allowing an easier identification of toxic causative chemicals when combined with bioassays.…”

“…There are used to determine the fractional potency of the mixture and are read out in potency equivalents. Recently, by use of such an EDA approach, Vrabie et al (2012) suggested that the predominant AhR agonists in crude and refined oils were aromatics and resins with log K ow of 5e8, such as alkylbenzenes, alkyl-PAHs, and/or aromatic chemicals containing nitrogen, sulfur, or oxygen atoms (including heterocyclic compounds). However, more than a thousand such chemicals would be expected in the complex mixtures of oil contaminated sediment.…”

Comprehensive study of a heavy fuel oil spill : modeling and analytical approaches to understanding environmental weathering

“…The larger polar constituents of HFOs from the refinery residue also have potential links to oil spill toxicity (Lubcke-von Varel et al, 2011;Vrabie et al, 2012). One study, by , focused specifically on the 2007 M/V Cosco Busan oil spill, and found this oil to be lethal at lower than expected concentrations; they found no explanation for this toxicity and pointed to changes in composition due to photochemistry within the uncharacterized high molecular weight compounds as a likely cause .…”