Toxicity of organic compounds from unresolved complex mixtures (UCMs) to primary fish hepatocytes

Abstract

Many environmental matrices contaminated with organic pollutants derived from crude oil or degraded petroleum contain mixtures so complex that they are typically unresolved by conventional analytical techniques such as gas chromatography. The resulting chromatographic features have become known as 'humps' or unresolved complex mixtures (UCMs). These UCMs often dominate the organic contaminants of polluted environmental samples: for example, in oil sands produced water up to 150mgL of 'naphthenic acids' appear as UCMs when examined by gas chromatography as the esters. In oil-contaminated mussels, aromatic hydrocarbon UCMs may comprise almost all of the total toxic hydrocarbons, with over 7000μgg dry weight reported in some samples. Over the last 25 years, efforts to resolve and thus identify, or at least to produce average structures, for some UCM components, have proved fruitful. Numerous non-polar UCM hydrocarbons and more polar UCM acids have been identified, then synthesised or purchased from commercial suppliers. As UCMs have been proposed to represent a risk to aquatic organisms, the need for assessment of the ecotoxicological effects and characterisation of the mode of action (MoA) of these environmental pollutants has arisen. In the present study, several chemicals with structures typical of those found in some UCMs, were assessed for their potential to disrupt membrane integrity, inhibit metabolic activity, activate the aryl hydrocarbon receptor (AhR), and activate the estrogen receptor (ER) in primary rainbow trout hepatocytes (Oncorhynchus mykiss). These endpoints were determined in order to screen for common toxic modes of action (MoA) in this diverse group of chemicals. The results from the in vitro screening indicated that of the endpoints tested, the predominant toxic MoA was cytotoxicity. EC values for cytotoxicity were obtained for 16 compounds and ranged from 77μM-24mM, whereof aliphatic monocyclic acids, monoaromatic acids, polycyclic monoaromatic acids and alkylnaphthalenes were the most toxic. The observed cytotoxicity of the chemicals correlated well with the hydrophobicity (LogK) suggesting that the toxicity was predominantly due to a non-specific MoA. Interestingly, two compounds induced the ER-mediated production of vitellogenin (Vtg) and six compounds induced the AhR-mediated Ethoxyresorufin-O-deethylase (EROD) enzymatic activity to >20% of the positive control; by doing so suggesting that they may act as ER or AhR agonists in fish. The heterogeneous group of 'UCM compounds' tested exhibited multiple MoA that may potentially cause adverse effects in fish. Additional studies to determine if these compounds may cause adverse effects in vivo at environmentally relevant concentrations, are warranted to identify if such compounds are indeed of potential environmental concern.

Characterizing Crude Oil Toxicity to Early-Life Stage Fish Based On a Complex Mixture: Are We Making Unsupported Assumptions?

“…Recent studies have proposed that the UCM contains a number of toxic compounds including branched alkyl benzenes, indanes, and tetralines. ,, Many other compounds in the UCM that exhibit log 10 K ow values in the range of 4–6 may also be toxic and co-occur with the commonly quantified PAHs including such groups as aliphatic naphthalenes, aliphatic monocyclic acids, monocyclic thiophenic carboxylic acids, and monoaromatic hydrocarbons. ,, Some of these compounds can be toxic to fish hepatocytes at low concentrations and at sublethal concentrations for mussels (Mytilus edulis). , The 22 compounds listed in Petersen et al are very hydrophobic with most exhibiting log 10 K ow values in the 3–6 range indicating a high potential for bioaccumulation. Booth et al determined an EC20 of 7 μg/L for mussels (reduced feeding) exposed to a mixture of branched alkyl benzenes, a major component of the UCM.…”

“…Recent studies have proposed that the UCM contains a number of toxic compounds including branched alkyl benzenes, indanes, and tetralines. 35,58,59 Many other compounds in the UCM that exhibit log 10 K ow values in the range of 4−6 may also be toxic and co-occur with the commonly quantified PAHs including such groups as aliphatic naphthalenes, aliphatic monocyclic acids, monocyclic thiophenic carboxylic acids, and monoaromatic hydrocarbons. 35,58,59 Some of these compounds can be toxic to fish hepatocytes at low concentrations 59 and at sublethal concentrations for mussels (Mytilus edulis).…”

“…35,58,59 Many other compounds in the UCM that exhibit log 10 K ow values in the range of 4−6 may also be toxic and co-occur with the commonly quantified PAHs including such groups as aliphatic naphthalenes, aliphatic monocyclic acids, monocyclic thiophenic carboxylic acids, and monoaromatic hydrocarbons. 35,58,59 Some of these compounds can be toxic to fish hepatocytes at low concentrations 59 and at sublethal concentrations for mussels (Mytilus edulis). 35,58 The 22 compounds listed in Petersen et al 59 are very hydrophobic with most exhibiting log 10 K ow values in the 3−6 range indicating a high potential for bioaccumulation.…”

Pyrolytic Remediation and Ecotoxicity Assessment of Fuel-Oil-Contaminated Soil

“…UCM contributed to the overall toxic effect of oil on marine amphibians [ 27 , 28 ]. Additionally, recent studies have indicated that UCM compounds may have adverse effects on aquatic organisms and are environmentally hazardous [ 29 ]. Research on UCM with complex composition and many compounds is still lacking.…”

Predicted and measured acute toxicity and developmental abnormalities in zebrafish embryos produced by exposure to individual aromatic acids

“…Binary and 6-compound mixtures of NA caused combined toxicity according to the concept of additivity, although slight deviations from additivity were observed at a few mixture concentrations. More recently, Petersen et al, (2017) reported the results from in vitro screening on fish cells, which indicated that of the endpoints tested, the predominant toxic mode of action (MoA) was cytotoxicity. EC50 values for cytotoxicity were obtained for 16 compounds and ranged from 77 μM-24 mM, whereof aliphatic monocyclic acids, monoaromatic acids, polycyclic monoaromatic acids were amongst the most toxic.…”