Passive Dosing of Petroleum and Essential Oil UVCBs—Whole Mixture Toxicity Testing at Controlled Exposure

Abstract

Petroleum products and essential oils are produced and used in large amounts and are categorized as "Substances of Unknown or Variable composition, Complex reaction products or Biological materials (UVCBs)." These UVCBs are notorious difficult-to-test substances, since they are complex mixtures of hydrophobic and volatile compounds. This study introduces two passive dosing (PD) approaches for whole UVCB toxicity testing:(1) headspace PD applies the UVCB and purified lipid oil as a donor to control exposure via the headspace and (2) silicone rod PD applies UVCB-loaded silicone rods to control exposure via an aqueous test medium and headspace. Headspace gas chromatography−mass spectrometry measurements were used to cross-validate the approaches at the saturation level and to confirm exposure and maintain mixture composition at varying donor concentration levels. Both approaches were applied to whole-mixture toxicity tests of petroleum and essential oil UVCBs with daphnia and algae. Finally, the observed toxicity was linked to concentrations in the donor and in lipid membranes at equilibrium with the donors. Dose−response curves were similar across the dosing approaches and tested species for petroleum products but differed by an order of magnitude between essential oils and PD systems. All observed toxic effects were consistent with baseline toxicity, and no excess mixture toxicity was observed.

Grouping of UVCB substances with dose-response transcriptomics data from human cell-based assays

“…Unfortunately, testing the material which is left after DMSO extraction presents numerous challenges because the solvents that would need to be used are incompatible with in vitro testing. Alternative delivery of the “whole substance” can be achieved through passive dosing ( Hammershoj et al, 2020 ; Trac et al, 2021 ); however, the methods to deliver complex UVCBs in small volume in vitro testing conditions have not been established yet. Thus, additional work is needed to improve the relevance of in vitro test methods for use in regulatory decisions on UVCBs.…”

The Next Frontier of Environmental Unknowns: Substances of Unknown or Variable Composition, Complex Reaction Products, or Biological Materials (UVCBs)

“…As UVCBs have multiple constituents of likely varying solubilities and percentage compositions, aquatic toxicity testing of UVCBs poses technical challenges for hydrophobic and/or volatile constituents. Thus, considerable studies in recent years have focused on developing improved toxicity testing methodologies for UVCBs, especially with respect to dosing of volatile, hydrophobic, and volatile and hydrophobic UVCBs, − as well as analyzing the effect of sample preparation on bioavailability …”

“…Thus, considerable studies in recent years have focused on developing improved toxicity testing methodologies for UVCBs, especially with respect to dosing of volatile, hydrophobic, and volatile and hydrophobic UVCBs, 124−126 as well as analyzing the effect of sample preparation on bioavailability. 127 Overall, modeling toxicity and testing of UVCBs have mostly focused on petroleum substances, [124][125][126]128 solvents, 86,129 and chlorinated paraffins. 23,130−132 Future method development and toxicity evaluations of other UVCBs are warranted.…”

Fate-directed risk assessment of chemical mixtures: a case study for cedarwood essential oil

“…Cedarwood oil was selected as a case study substance in the European Chemical Council (Cefic) long-range research initiative (LRI) ECO-42 project, 14 which has generated new data on biodegradation, 15 bioaccumulation potential for fish 13 and whole substance aquatic toxicity. 16 Characterisation data for the oil was provided by its distributor Givaudan UK Ltd and confirmed by gas-chromatography mass spectrometry (GC-MS). 13 Physical–chemical property data for the individual cedarwood oil constituents was taken from the literature or estimated using EPISuite (Table 1).…”

“…Baseline toxicity and thus absence of excess toxicity was supported for cedarwood oil based on the whole UVCB toxicity tests that were conducted within the ECO-42 project. 16 For a general application of our framework for UVCB risk assessment, potential excess toxicity needs to be evaluated carefully and additional experiments might be necessary particularly with regards to potential endocrine disruptive effects or carcinogenicity. 29 The evaluation of decision criteria 1 and 2 indicated that no further characterization data was needed to perform the fatebased risk assessment of the unidentied constituents.…”