Lubricating oils, used

Endpoint summary

Description of key information

Toxicokinetics of other lubricant base oils has been examined in rodents.  Absorption of other lubricant base oils across the small intestine is related to carbon chain length; hydrocarbons with smaller chain length are more readily absorbed than hydrocarbons with a longer chain length.  The majority of an oral dose of mineral hydrocarbon is not absorbed and is excreted unchanged in the faeces.  Distribution of mineral hydrocarbons following absorption has been observed in liver, fat, kidney, brain and spleen.  Excretion of absorbed mineral hydrocarbons occurs via the faeces and urine.  Based on the pharmacokinetic parameters and disposition profiles, the data indicate inherent strain differences in the total systemic exposure (~3 fold greater systemic dose in F344 vs SD rats), rate of metabolism, and hepatic and lymph node retention of C26H52, which may be associated with the different strain sensitivities to the formation of liver granulomas and MLN histiocytosis.

Key value for chemical safety assessment

Bioaccumulation potential:

no bioaccumulation potential

Additional information

Read across justification

Although other lubricant base oils (OLBOs) have not been assessed in toxicokinetic studies, they are similar in composition to highly refined mineral oils (white oils), so similar toxicokinetic properties would also be expected.

Mineral hydrocarbons (including other lubricant base oils) are chemically inert, and, when ingested, most of the mineral oil (98%) remains unabsorbed in the faeces. Data from studies of “Highly Refined Mineral Oil” (white oil) suggests that small amounts of mineral oil (~2%) are absorbed as such by the animal or human intestinal mucosa and further distributed throughout the body. A very small fraction may undergo further biochemical transformation.

"Sufficiently Refined" Other Lubricant Base Oils (IP 346 <3%)

In a basic toxicokinetic study performed by Baldwin et al., hydrotreated white oil was mixed with the diet of male and female rats in concentrations of 0, 10, 100, 500, 1000, 5000, 10000, and 20000 ppm for a period of 13 weeks. After sacrifice, haematological, clinical chemistry, gross necropsy, tissue residue, and histopathological examinations were preformed. There were no mortalities or adverse effects associated with feeding the rats oleum-treated white oil. Treatment related effects were generally dose-related and more marked in females than in males. After 90 days of treatment moderate multifocal granulomatous changes in mesenteric lymph nodes and liver were observed. Oleum-treated oil caused a greater pathological response then hydrotreated white oil. The hydrotreated white oil (applicable to sufficiently refined hydrocarbons, IP 346 < 3%) is metabolized to the corresponding fatty acids of the same carbon chain length as the parent carbons, suggesting omega oxidation.

A toxicokinetics study performed by Albro et al. evaluated absorption of hydrocarbon mixtures (IP 346 <3%). Simple mixtures of aliphatic hydrocarbons were administered to rats by gastric intubation at dose levels of up to 500 mg/kg b.w. The percentage retention of the aliphatic hydrocarbons was inversely proportional to the number of carbon atoms and ranged from 60% for C₁₄to 5% for C₂₈compounds. The major site of absorption was found to be the small intestine.

A toxicokinetics study performed by Ebert et al. evaluated distribution of tritiated mineral oil (IP 346 <3%) administered orally and via i.p. injections. Male and female rats were dosed with 0.66 mL of radiolabeled mineral oil for thirty-one consecutive days. Radioactivity was measured in extracted tissues after sacrifice. Results indicate that radioactivity is primarily found in liver, fat, kidney, brain, and spleen. Both oral and i.p. routes of administration exhibited the same characteristics of absorption.

A toxicokinetics study performed by Ebert evaluated excretion of tritiated mineral oil (IP 346 <3%) administered orally and via i.p. injections. Male and female rats were dosed with 0.66 mL of radiolabeled mineral oil for thirty-one consecutive days. Urine and faeces were collected and stored daily for radioactivity analysis. Eighty percent of the tritiated mineral oil administered orally was not absorbed but rather excreted in the faeces two days after treatment. Only 11% of the total dose administered by i.p. injection was excreted in the faeces during the first 8 days of the study. About 8% of the radioactivity administered orally and via intrapeitoneal injection was excreted in the urine during the week following drug administration.