Relevance of animal studies in the toxicological assessment of oil and wax hydrocarbons. Solving the puzzle for a new outlook in risk assessment

Abstract

Paraffin waxes and white mineral oils are distinct petroleum products separated from a common feedstock by crystallization, where only n-alkanes, iso-and cyclo-alkanes with a linear backbone of $ 20 carbon atoms long, selectively crystalize out from the oil to form the wax, which is solid at room temperature, whereas oils remain liquid. Up until the 90's, these differences were reflected in separated regulatory assessments. A paradigm shift occurred when Fischer 344 rats (F-344) developed liver epithelioid granuloma following exposure to low and medium viscosity oils or waxes. This lesion was used as common denominator between these products to be jointly assessed under the common term "mineral hydrocarbons -MHC", obviating compositional differences. This regulatory paradigm dominated for the next 30 years, exacerbated by the EFSA 2012 evaluation using the analytical term "MOSH" (mineral oil saturated hydrocarbons) which encompassed these products under single chromatography fraction. The reconstruction of historical developments, together with recent EFSA-sponsored studies of toxicity and accumulation and supporting literature, has allowed us to understand the etiology of the F-344 rat hepatic epithelioid granuloma, which is presented in an adverse outcome pathway (AOP). Considering chemical composition, it clearly demonstrates that the hepatic effects in F-344 rats caused by linear alkanes of waxes are irrelevant for humans. Waxes are thus not MOSH and should thus be evaluated on their own merit. The term MOSH should not include n-alkanes and be exclusively used to mineral oil fractions when considering their chemical makeup for a relevant human hazard assessment.

Update of the risk assessment of mineral oil hydrocarbons in food

“…The authors concluded that this was consistent with a lack of evidence for formation of epithelioid granulomas in humans. This conclusion is supported by a proposed adverse outcome pathway (AOP) analysis (Carrillo et al., 2021a,b). In humans, liver lesions consisted of accumulation of saturated hydrocarbons and lipoid granulomas of no clinical relevance.…”

Safety assessment of ‘waxes, paraffinic, refined, derived from petroleum‐based or synthetic hydrocarbon feedstock, low viscosity’ for use in food contact materials

“…However, Carrillo et al. ( 2021 ) considered Wax 4 (Section 3.1.1 ) to be representative of one of the paraffin waxes tested in Shubik et al. (1962), based on the same overall physical properties, the chain length range and the content of n ‐, mono‐branched and monocyclic alkylated cycloalkanes.…”

“…However, it was not demonstrated that the metabolism ended with complete degradation. Recently, Carrillo et al (2021) proposed a mode of action analysis within an Adverse Outcome Pathway framework to better explain how the decreased metabolism, leading to an accumulation of n-alkanes in the Fischer 344 liver, were the key events triggering the production of wax crystals with the epithelioid granuloma formation (possibly triggering inflammation). The accumulation in humans, mainly in adipose tissue, does not reflect the accumulation in rats, especially the Fischer 344 strain, mainly due to the time course difference in hepatic clearance (Barp et al, 2017;Cravedi et al, 2017).…”

“…No certificate of analysis of the tested waxes was provided. However, Carrillo et al (2021) considered Wax 4 (Section 3.1.1) to be representative of one of the paraffin waxes tested in Shubik et al (1962), based on the same overall physical properties, the chain length range and the content of n-, monobranched and monocyclic alkylated cycloalkanes. Consequently, the authors claimed that the wax tested in Shubik et al (1962) was worst-case for its MOAH content (0.09% in Wax 4 compared to 0.01% in Wax 1).…”

Evaluating the in vitro developmental toxicity potency of a series of petroleum substance extracts using new approach methodologies (NAMs)

“…The type and quantity of aromatic constituents in petroleum substances vary depending on the source of the crude oil feedstock and the processing conditions applied during their manufacturing process (Mackerer et al 2003 ; Tsitou et al 2015 ; Carrillo et al 2022 ). For example, aromatic extracts, obtained upon solvent extraction of distillates or the residue from a vacuum tower, contain a relatively high concentration of dimethyl sulfoxide (DMSO)-extractable aromatics (6.6–20.3%, mostly 3- to 7-ring PACs) (HPV 2012 ; Carrillo et al 2021 ). Whereas, highly refined petroleum products, such as highly refined base oil (HRBO) and petroleum derived-waxes, obtained upon dewaxing, deoiling and/or hydrotreatment of base oil process, contain mainly highly alkylated 1- to 2-ring aromatics because the hazardous 3- to 7-ring aromatic compounds in these products are removed during the refinement (Fig.…”