Acute, Subchronic, and Developmental Toxicological Properties of Lubricating Oil Base Stocks

Abstract

Lubricating oil base stocks (LOBs) are substances used in the manufacture of finished lubricants and greases. They are produced from residue remaining after atmospheric distillation of crude oil that is subsequently fractionated by vacuum distillation and additional refining steps. Initial LOB streams that have been produced by vacuum distillation but not further refined may contain polycyclic aromatic compounds (PACs) and may present carcinogenic hazards. In modern refineries, LOBs are further refined by multistep processes including solvent extraction and/or hydrogen treatment to reduce the levels of PACs and other undesirable constituents. Thus, mildly (insufficiently) refined LOBs are potentially more hazardous than more severely (sufficiently) refined LOBs. This article discusses the evaluation of LOBs using statistical models based on content of PACs; these models indicate that insufficiently refined LOBs (potentially carcinogenic LOBs) can also produce systemic and developmental effects with repeated dermal exposure. Experimental data were also obtained in ten 13-week dermal studies in rats, eight 4-week dermal studies in rabbits, and seven dermal developmental toxicity studies with sufficiently refined LOBs (noncarcinogenic and commonly marketed) in which no observed adverse effect levels for systemic toxicity and developmental toxicity were 1000 to 2000 mg/kg/d with dermal exposures, typically the highest dose tested. Results in both oral and inhalation developmental toxicity studies were similar. This absence of toxicologically relevant findings was consistent with lower PAC content of sufficiently refined LOBs. Based on data on reproductive organs with repeated dosing and parameters in developmental toxicity studies, sufficiently refined LOBs are likely to have little, if any, effect on reproductive parameters.

Characterization of the toxicological hazards of hydrocarbon solvents

“…There is an unpublished developmental toxicity study that assessed the potential effects of a C16-C30 mineral oil (60% paraffins, 40% cycloparaffins) in Sprague-Dawley rats (summarized in Dalbey et al 2014). The study compared the effects following exposure on gestational days 6-19 by oral (5000 mg/kg/day), dermal (2000 mg/kg/day), or inhalation (1000 mg/m 3 as aerosol, 6 hours/day).…”

“…Accordingly, the no-effect levels/concentrations were the highest doses/concentrations used in this study. In separate studies (also summarized in Dalbey et al 2014), the developmental toxicity of a C16-C30 mineral oil (60% paraffins, 40% cycloparaffins) was evaluated in a one generation reproductive/ developmental toxicity study in which rats were exposed to test material by dermal administration in daily doses of 125, 500, or 2000 mg/kg bw. There were no differences in mean numbers of implantation sites, live pups/litter, live-birth indices (total number offspring born), and survival of offspring on postnatal days 4 and 21.…”

“…Similarly, dermally-administered hydrodesulfurized kerosene did not lead to reproductive or developmental effects in a study involving dermal administration at levels up to 495 mg/kg/day, the highest doses applied (Schreiner 1997). An unpublished one-generation reproductive toxicity study of a C16-C30 mineral oil (summarized in Dalbey et al 2014) was conducted to evaluate the reproductive performance (gonadal function, all 4 stages of the estrus cycle, fertilization, implantation, length of gestation, and parturition) in Sprague-Dawley rats. The animals were exposed to test material by dermal administration at levels of 125, 500, or 2000 mg/kg bw/day.…”

The Mammalian Toxicological Hazards of Petroleum-Derived Substances

“…These oils are further refined usually by solvent extraction, a process that selectively removes high-boiling aromatic components resulting in noncarcinogenic base stocks or hydrogenation to remove the aromatics or convert them to saturated constituents. The LBOs, as currently manufactured do not contain PACs at hazardous levels, are not carcinogenic, 76 and, as demonstrated by experimental studies conducted as part of the HPV program along with other data, 77 do not produce either target organ or developmental toxicity. Because the unrefined LBOs contain PACs and are carcinogenic, it seems reasonable to assume that they could also produce target organ and developmental effects in repeated dose studies.…”

Mineralöle (Erdöl), stark raffiniert [MAK Value Documentation in German language, 2018]

“…72623-83-7 (C > 25) wurde eine Viskosität von 550 mm 2 /s bei 40 °C angegeben (Dalbey et al 2014), es ist also hochviskos und wird kaum oral resorbiert. Die anderen zwei Mineralöle, die in dieser Begründung bewertet werden, sind noch viskoser, da sie eine höhere C-Zahl aufweisen.…”