White mineral oil (petroleum)

Endpoint summary

Description of key information

Short description of key information on bioaccumulation potential result:

The toxicokinetic activity of white mineral oil was investigated in Fischer 344 and Sprague- Dawley rats and human volunteers. In key animal oral toxicity studies that investigated the toxicokinetic activity of highly refined base oils, no mortalities were observed. HRBO was not well absorbed overall, with roughly 3-5% absorbed and the rest excreted in the faeces. A pronounced rat strain difference in toxicokinetics was observed between F-344 and SD rats, with the former absorbing and retaining significantly greater amounts of HRBO. The only treatment-related effects were moderate multifocal granulomatous changes in mesenteric lymph nodes and liver. In further key studies that tested toxicokinetic activity, multifocal granulomatous changes in mesenteric lymph nodes and liver were observed. The major sites of HRBO accumulation were liver, fat, kidney, brain, spleen, and small intestine. Based on the toxicokinetic parameters and disposition profiles, the data indicate inherent strain differences in the total systemic exposure (~4 fold greater systemic dose in F344 vs SD rats), rate of metabolism, and hepatic and lymph node retention of HRBO hydrocarbons, which may be associated with the different strain sensitivities to the formation of liver granulomas and MLN histocytosis. In contrast, a toxicokinetic study conducted in humans showed that the blood concentration of white mineral hydrocarbons was less than the limit of detection (0.16 µg/mg), suggesting negligible absorption at a dietary exposure of 1 mg/kg.

Key value for chemical safety assessment

Bioaccumulation potential:

low bioaccumulation potential

Additional information

There have been a number of studies that indicate that highly refined base oils are absorbed from the gut, are distributed to the liver, kidneys, and mesenteric lymph nodes, and excreted primarily via faeces. Baldwin et al. (1992; Klimisch score=2) fed five F-344 rats of each sex diets containing either oleum-treated white oil (OTWO) or hydrotreated white (HTWO) oil for 90-days at a dietary concentration of 20,000 ppm or 2% (~2000 mg/kg). At the end of the study, tissue hydrocarbon levels were measured in the liver and kidneys and the values were compared to analyses that were carried out on five rats of each sex that had been fed control diet only. The levels of hydrocarbon in the control animals were below the detectable levels (<0.2 mg/kg). In the rats fed a diet containing white oil, tissue concentrations of hydrocarbons were higher in females than males (3.7 – 5.2 times) and slightly higher in animals fed oleum-treated oil. Analysis of liver and mesenteric lymph node for total hydrocarbon residues were below detectable limits in control tissues (lod <0.2). The levels of oleum treated-white oil (OTWO) in liver were 2.36 ± 0.22 mg/g in males, and 11.5 ± 2.36 mg/g in females. The levels of OTWO detected in the mesenteric lymph node were 1.76 ± 0.91mg/g in male and 6.55 ± 2.20 mg/g in female. The hydrotreated white oil residues (HTWO) in the liver were 1.76 ± 54mg/g and 4.22 ± 1.30mg/g in male and female, respectively. The level of HTWO detected in the mesenteric lymph node was <1.0 mg/g in male and 4.22 ± 1.64 mg/g in female. The findings by Baldwin et al. (1992) were confirmed by Smith (1996) and Firriolo et al. (1995) (see the section on oral repeated dose toxicity).

 

Part of the study reported by Smith (1996) was designed to determine the concentrations of highly refined base oil (HRBO) in selected tissues following 90-days feeding with diets containing HRBO. In this study, five F-344 rats of each sex were fed control diet or diet containing 6 white oils (approximate viscosity ranged from 10 to 100) and 3 waxes and coconut oil. Mineral hydrocarbon test materials were N10A, N15H, P15H, N70A, N70H, P100H: N = naphthenic, P = paraffinic, A = acid- treated and H = hydrogenated (also described in more detail in the section on repeat-dose toxicity). The rats were exposed to the oils for 90 days at a dietary concentration of 2.0%. Extra groups of rats (5 of each sex) were fed control diet or coconut oil or one of the six oils for 90 days followed by exposure to control diet only for an additional 28 days. These extra groups were used to determine whether effects were reversible. HRBO residues were found in the livers of all groups fed white oil, except females fed P 100 H (highest molecular weight material tested). Accumulation in the liver was greater in females than males, an observation described previously by Baldwin et al. (1992). 

In the liver, the HRBO tissue content of females treated with N10A, N15H, P15H, N70A, N70H and P70H ranged from 1.0 to 4.3 mg/g liver, which was 4-5 times greater than males (0.3-1.0 mg/g liver in males). After a one month reversal period there was some evidence for a decrease of the hepatic levels in both sexes for most of the test materials tested, however some increase was seen in females treated with P15H, N70A and N70H.

With P100H, the concentration of saturated hydrocarbons in mesenteric lymph nodes was in a range between 0.6 mg/g tissue and 3 mg/g tissue, and was higher in females than males. After a one month reversal period, no reduction of saturated hydrocarbons was observed. Likewise, the HRBO content in peri-renal fat was increased more in female than in male treated with N10, N15H and P15H (0.42 - 0.44 mg/g tissue in females). Although there was some evidence of a reduction in HRBO levels after a one month reversal period, elevated levels nevertheless still remained (0.26 - 0.44 mg/g tissue in females).

 

Trimmer et al. (2004) investigated the deposition of mineral hydrocarbon in liver, kidneys, mesenteric lymph nodes and spleen of female Fischer 344 exposed to P70H and P100H via diet at received dose levels of 60, 120, 240 and 1200 mg/kg/bw for up to 2 years. For one group the exposure to the oils was stopped after 12 months. During the following year the concentration in the liver decreased significantly, but did not reach the level of the control group. The proportion of the mineral hydrocarbons persisting after 12 months depuration period was around 10-15% of the initial amount.

 

Firriolo et al. (1995) carried out a 90-day study in female rats (Fischer 344 and CRL-CD Sprague- Dawley) exposed to a P15H oil incorporated into diet at 2000 or 20000 mg/kg. The study showed a dose and strain related increase in the level of hydrocarbons in the liver and mesenteric lymph nodes from both rat strains. Levels present in the mesenteric lymph nodes was approximately 2-3 fold lower for Sprague Dawley and 5 fold lower for Fischer 344 strain.

 

The disposition and toxicokinetics of ¹⁴C-labeled eicosanylcyclohexane in female F-344 and Sprague-Dawley rats have been assessed (Sipes & Halladay, undated; Halladay et al., 2002, Klimisch score = 2). Eicosanylcyclohexane was selected because it is a C26 hydrocarbon present in mineral oils and its toxicokinetic behaviour was assumed to be representative of the constituents of complex white oils. For the disposition study, fasted female rats of both strains were given a single oral dose by gavage of 2 ml/kg bw of a 4:1 mixture of olive oil and food grade paraffinic white oil containing [1-¹⁴C]-eicosanylcyclohexane and a non-absorbable marker [1,2-³H] polyethylene glycol 4000. After dosing, the animals were held in metabolism cages over the following 96-hours. Urine, faeces and exhaled air were collected at 8, 16, 24, 48, 72 and 96 hours and were analyzed for total radioactivity. Ninety six hours post-dosing the animals were killed, and blood, liver, mesenteric lymph nodes and contents of the bladder and intestines were collected and analysed for total radioactivity.

 

For the toxicokinetic study [1-¹⁴C]-eicosanylcyclohexane in a mixture of olive oil and white oil (4:1) was administered as a single oral dose (1.8 g/kg) to female F-344 and Sprague-Dawley rats with indwelling jugular vein catheters. The animals were then held in metabolism cages for the collection of urine and faeces at 8, 16, 24, 48, 72 and 96 hours. At the same times, blood samples were taken via the catheters and analysed for total radioactivity. Also at these times, at least three rats were killed and blood, liver, mesenteric lymph nodes and the contents of intestines and bladder were collected and analysed for total radioactivity.

 

The bioavailability of total [¹⁴C] was greater in F-344 rats than in Sprague-Dawley rats as indicated by the area under the curve (AUC) of the plot of plasma concentration versus time.  F-344 rats had a higher maximum blood concentration (C_max) for total [¹⁴C], and a longer time to achieve C_max compared to Sprague-Dawley rats. Faecal excretion was the major route of elimination for both strains. By 96 hours, 82% (F-344) and 87% (SD) of the dose was excreted in the faeces, but the rate of excretion was lower in the F-344 rats. Seventy percent of the label had been eliminated by 16 hours in the Sprague-Dawley rat, whereas, in the F-344 rat 11% of the dose was eliminated in 16 hours and 75% was eliminated in 48 hours. Urinary excretion was the second major route of excretion although the urinary profiles were different in the two strains. The Sprague-Dawley rats eliminated the radiolabel in the urine by 24 hours whereas excretion by the F-344 was linear over time during the 96 hour monitoring period and at this time only 7% of the administered dose was accounted for. The maximum amount of radioactivity in the liver was 2% at 8 hours for the Sprague-Dawley rat compared to 4% at 24 hours for the F-344 rats. Even after 96 hours 3% of the administered dose remained in the F-344 rat livers. The amount of radioactivity in the mesenteric lymph nodes was similar for both rat strains until 96 hours. At that time the percentage of the administered dose increased from 0.002% to 0.02% in the Sprague-Dawley rat.

 

The above single dose oral studies (Sipes & Halladay) were repeated using a 10-fold lower dose (Sipes and Halladay, 2001; Halladay et al., 2002, Klimisch score=2). The procedures were the same as those described in the study above except that the dose administered was 0.2 mL/kg. The results differed from those in the high dose in that in the F-344 rats the radioactivity in blood showed a biphasic profile with C_max at 4 and 16 hours. This was in contrast to the profile with the high dose study (C_max of 18 hours). The Sprague-Dawley rats had similar C_max values in both the high and low dose studies (5-5.6 hours). As with the high dose studies, the AUC was greater for F-344 rats than for Sprague-Dawley rats. Faecal excretion was the major route of elimination with little difference between the two strains (76% F-344, 72% Sprague-Dawley). The differences in patterns of urinary excretion and liver retention of radioactivity in the two strains were similar to those which had been observed in the high dose study. Retention of radiolabel in the mesenteric lymph nodes also differed in the two strains, but the difference was less than had been seen in the high dose study (2-fold in the low dose study).

 

Further information on strain differences in the single dose toxicokinetics of white oil (P15H) is available from TNO Quality of Life (2010) and Boogaard et al. (2012). In this study, female F-344 rats were dosed via oral gavage at 0, 20, 200, and 1500 mg Pl5H white oil/kg body weight while female Sprague Dawley rats received 0, 200 and 1500 mg P15H white oil/kg body weight. Blood samples (1, 2, 4, 8, 16, 24, 48, 96 hours) and livers (24, 48 and 96 hours) were collected at regular intervals over 4 days following treatment. The concentration of P15 white oil in blood and liver was measured by GC x GC – MS analysis and quantified based on the C19-C24 range of alkanes present. Blood concentrations were observed to increase to a maximum at 4 hr and then seen to decrease with time. In the F-344 strain, the blood concentrations were found to be clearly higher than in the Sprague-Dawley rat at dose levels of 200 and 1500 mg per kg body weight. Additionally, at sacrifice, F-344 rats in the 200 and 1500 mg/kg dose group exhibited higher concentrations of P15 white oil in liver and arterial blood. A measure of systemic exposure, the AUC_0-∞,was higher by a factor of 4 in F-344 rats compared to Sprague-Dawley rats in both 200 (292 ± 18 vs. 62 ± 15 h*mg/L) and 1500 (700 ± 140 vs. 146 ± 49 h*mg/L) mg/kg body weight dose groups. The Cmax in F-344 rats was also higher than that observed in Sprague-Dawley rats. In the liver, maximum concentrations of the test material were seen 24 hours post exposure. Both Cmax and AUC at 200 mg/kg (4031 vs. 2267 h*mg/L) and 1500 mg/kg (8608 vs. 3124 h*mg/L) were higher in the F-344 rats than in Sprague-Dawley rats. However, dose-proportional kinetics was not observed in either strain. The results of this study confirm the strain-dependent differences in disposition of white oil reported by other studies and discussed above, and demonstrate that at doses of 200 and 1500 mg/kg body weight P15 white oil is more bioavailable in female F-344 rats than in female Sprague-Dawley rats.

  

The metabolism of HRBO was investigated by several authors. It was demonstrated that alkenes are converted to the corresponding fatty alcohols and acids by small intestine and liver (Mitchell and Hübscher, 1968, Ichihaea et al. 1981; McCarthy, 1964; Kusunose et al 1969; Perdu- Duran and Tulliez, 1985, EFSA 2012) and that C16 and C18 hydrocarbons (constituents of white oils) are metabolised to the fatty acids of the same carbon chain length as the parent hydrocarbons, suggesting a process of omega oxidation (Baldwin et al, 1992; Klimisch score=2). The oxidative metabolism showed some species differences and it is mediated by the cytochrome P450 system (Ichiahara et al. 1981, Perdu-Durand and Tulliez, 1985).

Cravedi et al. (2011) investigated the oxidation rates of radiolabelled heptadecane in Sprague Dawley, Wistar and Fischer 344 using liver microsome incubations. The highest rate of hepatic hydroxylation occurred in Wistar, then in Sprague Dawley and finally in Fischer 344 rats. No difference between male and female was observed. Later, the biotransformation of radiolabelled n-heptadecane, pristine and dodecylcyclohexane was investigated in rats (Sprague Dawley, Wistar, Fischer 344) and humans using hepatic microsomes. In contrast with the previous study, no difference between strains was observed and the biotransformation in human females was significantly higher than Fischer 344 female rats (Cravedi and Perdu, 2012).

(A toxicokinetics study performed by Abro et al. (1970) evaluated absorption of hydrocarbon mixtures (IP 346 <3%). Simple mixtures of aliphatic hydrocarbons were administered to CD male 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 C₁₄ to 5% for C₂₈ compounds. The major site of absorption was found to be the small intestine.

A toxicokinetic study performed by Ebert et al. (1966) evaluated the distribution of mineral oil administered orally and via i.p. injection. Male and female Sprague-Dawley and Holtzman rats were treated orally and via i.p. injection with 0.66 mg/kg bw of non-labelled mineral oil for 31 consecutive days. Tritiated mineral oil was given on the thirty-second day,as at final dose. Both oral and i.p. routes of administration exhibited the same characteristics of absorption. Results indicated that radioactivity was found in liver, fat, kidney, brain, and spleen. After oral administration, the concentration of tritiated mineral oil decreased rapidly to 0.3% within 2 days post treatment and very slowly by day 21 indicating a very low absorption. After i.p administration the extraction was very slow: 11% was found in faeces within 8 days post treatment and negligible traces were found in urine.

In a study designed to investigate the absorption and kinetics of P15H white oil in humans, nine female volunteers (age 18 -35 years) were administered a single oral dose of a mixture of white oil- tetracosane via gelatine capsule at a mean received dose of 1.00 +/- 0.11 mg P15H/kg BW (TNO Quality of Life, 2011 and Boogaard et al. (2012). Blood was sampled at regular intervals over 7 days post-treatment and analysed using two-dimensional gas chromatography-mass spectrometry (GCxGC-MS). The subjects reported no clinical signs or adverse symptoms, however analytical results showed that the concentration of white oil in blood was below the average within laboratory detection limit (0.163 ug/mL) at all time points. While no kinetic information could be derived from the data, the results nonetheless put an upper bound on the concentration of white oil in blood following lows level of human ingestion.

References

1. Baldwin, M., Berry, P., Esdaile, D., Linnett, S., Martin, J., Peristianis, G., Priston, R., Simpson, B., and Smith, J.(1992). Feeding studies in rats with mineral hydrocarbon food grade white oils.

Toxicologic Pathology, 20, (3) part 1, 426-435.

 

2. Boogaard PJ, Goyak KO, Biles RW, van Stee LL, Miller MS, Miller MJ. (2012). Comparative toxicokinetics of low-viscosity mineral oil in Fischer 344 rats, Sprague-Dawley rats, and humans--implications for an Acceptable Daily Intake (ADI). Regul Toxicol Pharmacol. 2012 Jun;63(1):69-77.

 

3. Cravedi JP and Perdu E, (2012). In vitro metabolic study on alkanes in hepatic microsomes from

humans and rats. EFSA External Scientific Report. Supporting Publication, 263, 64 pp.

 

4. Cravedi J, Thibaut R, Tulliez J and Perdu E, (2011). Comparative in vitro study of the biotransformation of n-alkanes by liver and small intestine microsomes from different rat strains. Toxicology Letters, 205, S188-S188.

 

5. Ebert, A. J., Schleiffer, C. R., and Hess, S. M. (1966). Absorption, deposition and excretion of 3H-mineral oil in rats. Journal of Pharmaceutical Sciences 55, 923-929 1966

6. EFSA (2012). Scientific Opinion on Mineral Oil Hydrocarbons in Food. EFSA Panel on Contaminants in the Food Chain (CONTAM). European Food Safety Authority (EFSA) Parma, Italy. EFSA Journal 2012;10(6):2704

7. Firriolo JM, Morris CF, Trimmer GW, Twitty LD, Smith JH and Freeman JJ, (1995). Comparative 90-day. Feeding study with low-viscosity white mineral oil in Fischer-344 and Sprague-Dawley-derived CRL:CD rats. Toxicologic Pathology, 23, 26-33.

 

8. Halladay JS, Mackerer CR, Twerdok LE and Sipes IG, (2002). Comparative pharmacokinetic and disposition studies of [1-14C]1-eicosanylcyclohexane, a surrogate mineral hydrocarbon, in female Fischer-344 and Sprague-Dawley rats. Drug Metabolism and Disposition: The Biological Fate of Chemicals, 30, 1470-1477.

  

9. Ichihara K, Ishihara K, Kusunose E and Kusunose M, (1981). Some properties of a hexadecane hydroxylation system in rabbit intestinal mucosa microsomes. Journal of Biochemistry, 89, 18211827.

10. Kusunose M, Ichihara K and Kusunose E, (1969). Oxidation of n-hexadecane by mouse liver microsomal fraction. Biochimica et Biophysica Acta, 176, 679-681.

11. McCarthy RD, (1964). Mammalian Metabolism of Straight-Chain Saturated Hydrocarbons. Biochimica et Biophysica Acta, 84, 74-79.

 

12. Mitchell MP and Hubscher G, (1968). Oxidation of n-hexadecane by subcellular preparations of guinea pig small intestine. European Journal of Biochemistry, 7, 90-95.

 

13. Perdu-Durand EF and Tulliez JE, (1985). Hydrocarbon hydroxylation system in liver microsomes from four animal species. Food and Chemical Toxicology, 23, 363-366.

 

14. Smith JH, Mallett AK, Priston RA, Brantom PG, Worrell NR, Sexsmith C, Simpson BJ.(1996).

Ninety-day feeding study in Fischer-344 rats of highly refined petroleum-derived food-grade white oils and waxes. Toxicol Pathol. 1996 Mar-Apr;24(2):214-30.

 

15. Trimmer GW, Freeman JJ, Priston RA and Urbanus J, (2004). Results of chronic dietary toxicity studies of high viscosity (P70H and P100H) white mineral oils in Fischer 344 rats. Toxicologic Pathology, 32, 439-447.