National Toxicology Program, Department of Health and Human Services
Report on Carcinogens, Fifteenth Edition For Table of Contents, see home page: http://ntp.niehs.nih.gov/go/roc
For denitions of technical terms, see the Glossary.
Mineral Oils: Untreated and Mildly Treated
CAS No.: none assigned
Known to be human carcinogens
First listed in the First Annual Report on Carcinogens (1980)
Carcinogenicity
Untreated and mildly treated mineral oils are known to be human car-
cinogens based on sufficient evidence of carcinogenicity from stud-
ies in humans.
Cancer Studies in Humans
e carcinogenicity of exposure to untreated and mildly treated min-
eral oils has been evaluated in numerous studies in a variety of oc-
cupations, including metal working, jute processing, mulespinning,
newspaper press operation, and other newspaper work. Exposure
to mineral oils was consistently and strongly associated with an in-
creased risk of cancer of the scrotum and skin (squamous-cell carci-
noma) for many occupations, including metal worker, mulespinner,
and jute processor. An analysis of a series of 344 cases of scrotal can-
cer occurring from 1936 to 1976 in the West Midlands region of Eng-
land reported that 62% of the men had been exposed to mineral oils.
Epidemiological studies (case-control, cohort, and proportional mor-
tality studies) in metal workers have reported excesses of gastroin-
testinal, sinonasal, and bladder cancer, in addition to skin and scrotal
cancer. Some but not all studies (case-control, cohort, and propor-
tional mortality studies) of workers in the printing industry have re-
ported significantly increased incidences of death from cancer of the
lung, rectum, buccal cavity, and pharynx. e International Agency
for Research on Cancer concluded that there was sufficient evidence
for the carcinogenicity of untreated and mildly treated mineral oils
in humans (IARC 1984, 1987).
Cancer Studies in Experimental Animals
ere is sufficient evidence for the carcinogenicity of some un-
treated and mildly treated mineral oils from studies in experimental
animals. Evaluation of the carcinogenicity of mineral oils in experi-
mental animals has mainly involved experiments in which petroleum-
derived base oils and formulated products were applied repeatedly to
the skin of mice; however, some types of mineral oil preparations were
studied in other species and by other routes of exposure. Vacuum-
distillate fractions, acid-treated oils, mildly solvent-refined oils, mildly
treated hydrotreated oils, aromatic oils (including solvent extracts
and high-boiling-point fractions of catalytically cracked oils), and
some cutting oils caused skin tumors in mice. High-boiling-point
fractions of cracked oils also caused skin tumors in rabbits and mon-
keys (IARC 1984, 1987).
Properties
Mineral oils include lubricant base oils and products derived from
them. e physical properties of lubricant oils vary widely, but gen-
erally are defined by crude oil source, carbon number distribution,
boiling range, and viscosity. Mineral oils, which are refined from pe-
troleum crude oils, are complex mixtures of straight- and branched-
chain paraffinic, naphthenic, and aromatic hydrocarbons with 15 or
more carbons and boiling points in the range of 300°C to 600°C; boil-
ing points of up to 815°C have been reported for heavier oils. e vis-
cosity of lubricant oils is described as “light” or “heavy” depending
upon whether the maximum viscosity at 37.8°C is less than or equal
to 20.5mm
2
/sec (centistokes). e density of mineral oils at 15°C
ranges from 0.820kg/L for light paraffinic base and process oils to
just over 1.0kg/L for high aromatic base and process oils. e com-
plete description of a mineral oil must include the nature of the final
treatment step, which determines whether the material is mildly or
severely treated during the refining process. Medicinal white min-
eral oils, which are pharmaceutical- and food-grade materials, are
highly refined and free of all aromatic and unsaturated compounds.
As highly refined oils, these products are not covered under this list-
ing (IARC 1984).
Mineral oils are insoluble in water and alcohol, but soluble in
benzene, chloroform, ether, carbon disulfide, and petroleum ether.
Paraffinic crude oils are characterized by high wax content, high nat-
ural viscosity index (the rate of change of viscosity over a given tem-
perature range), and relatively low aromatic hydrocarbon content.
Naphthenic crude oils are generally low in wax content and rela-
tively high in cycloparaffins and aromatic hydrocarbons. All crude
oils contain some polycyclic aromatic hydrocarbons, and the propor-
tions and types of these compounds in finished base oils are deter-
mined primarily by the refining processes (IARC 1984). Mineral oils
generally do not present a fire hazard and must be preheated before
ignition will occur (HSDB 2009).
Use
Mineral oils are used primarily as lubricant base oils to produce
further refined oil products, including engine oils, automotive and
industrial gear oils, transmission fluids, hydraulic fluids, circulat-
ing and hydraulic oils, bearing oils, machine oils, machine-tool oils,
compressor and refrigerator oils, steam-engine oils, textile machine
oils, air-tool oils, metalworking oils (cutting oils, roll oils, can-form-
ing oils, and drawing oils), rust-preventative oils, heat-treating oils,
transformer oils, greases, medicinal and technical-grade white oils,
and processing oils (product extenders, processing aids, carriers and
diluents, water repellents, surface-active agents, batching oils, mold-
release oils, and wash oils). ese oils are used in manufacturing
(78.5% of the oils produced), mining (5.0%), construction (1.8%), and
miscellaneous industries (14.7%). About 57% of the lubricating oils
produced are used by the automotive industry, and the remaining
43% by other industries. In the automotive industry, lubricating oils
are used as multigrade engine oils (23% of the lubricating oils pro-
duced), monograde engine oils (22%), transmission and hydraulic
fluids (8%), gear oils (2%), and aviation oils (1%). In other industries,
lubricating oils are used as general industrial diesel engine oils (19%),
process oils (13%), metalworking oils (4%), railroad diesel engine oils
(3%), and marine diesel engine oils (2%) (IARC 1984).
Production
In 1981, about 19 billion pounds of mineral oil products were used
in the United States (NPRA 1981), including 16.2 billion pounds of
lubricating oils, 1.5 billion pounds of waxes, 814 million pounds of
aromatic oils, and 462 million pounds of greases. In 2009, mineral
oils were available from 28 U.S. suppliers (ChemSources 2009). In
1984, the United States imported 17,000kg (37,000 lb) and exported
75,000kg (165,000lb) of mineral oil (type not specified) (HSDB 2009).
No more recent data specific to U.S. imports or exports of mineral
oils were found.
Exposure
e primary routes of potential human exposure to mineral oils are
inhalation, ingestion, and dermal contact. e major hydrocarbon
constituents of lubricant base oils and derived products occur nat-
urally in crude petroleum. e general population potentially is ex-
posed to unused and used mineral oils that occur naturally or are
present as environmental contaminants. About 2billion liters (528
National Toxicology Program, Department of Health and Human Services 2
Report on Carcinogens, Fifteenth Edition
For denitions of technical terms, see the Glossary.
million gallons) of used lubricating oils are released into the envi-
ronment every year, including 750 million liters (198 million gallons)
used as road oil or in asphalt (IARC 1984).
Occupational exposure to mineral oils may occur among work-
ers employed in the manufacture of automobiles, airplanes and
parts, steel products, screws, pipes, precision parts, and transform-
ers, as well as workers employed in brass and aluminum produc-
tion, engine repair, copper mining, and newspaper and commercial
printing (IARC 1984). e National Occupational Exposure Survey
(conducted from 1981 to 1983) estimated that 1,009,473 workers,
including 392,294 women, potentially were exposed to mineral oils
(NIOSH 1990). e National Institute for Occupational Safety and
Health reported the presence of mineral oils in the occupational envi-
ronment of several plants in the 1970s. e concentration of cutting-
oil mist was reported to be 0.37 to 0.55mg/m
3
for polishing of aircraft
engine blades, 0.4 to 6.0mg/m
3
for machining of rough iron castings
into automotive parts, 1.1 to 20mg/m
3
for manufacture of aircraft
components, 0.3 to 1.3mg/m
3
for manufacture of automotive parts,
from less than 0.03 to 0.8mg/m
3
for fabrication of precision metal
parts, and from less than 0.035 to 3.1mg/m
3
for milling and machin-
ing operations. e concentration of transformer oil in air was re-
ported to be 0.1 to 1.4mg/m
3
for the manufacture and overhauling
of large transformers (IARC 1984).
Regulations
Consumer Product Safety Commission (CPSC)
Products containing 10% or more of petroleum distillates require special labeling because of aspiration
hazard.
Special packaging is required for certain household products containing 10% or more petroleum
distillates and with a viscosity less than 100 Saybolt Universal seconds.
Environmental Protection Agency (EPA)
Clean Water Act
Procedures, methods, equipment, and other requirements have been established to prevent the
discharge of all types of oils (including mineral oil) from all types of non-transportation-related
facilities.
Products of mineral oil origin at levels that will cause interference are banned from discharge to
publicly owned treatment works.
Food and Drug Administration (FDA, an HHS agency)
Some over-the-counter drugs and products containing mineral oil must contain a warning label.
Restrictions on the use of mineral oil in food preparation and in packaging materials are prescribed in
21 CFR 172, 173, and 175-179.
When used as a lubricant with incidental food contact, mineral oil levels shall not exceed 10ppm.
Drugs for internal use containing mineral oil must have a warning label.
Limitations on the use of mineral oil in drugs for use in animal feed are prescribed in 21 CFR 558.
Limits on the use of mineral oil as an additive in feed and drinking water of animals are prescribed in
21 CFR 573.
Occupational Safety and Health Administration (OSHA, Dept. of Labor)
While this section accurately identies OSHA’s legally enforceable PELs for this substance in 2018,
specic PELs may not reect the more current studies and may not adequately protect workers.
Permissible exposure limit (PEL)= 5mg/m
3
for mineral-oil mist.
Guidelines
American Conference of Governmental Industrial Hygienists (ACGIH)
Threshold limit value – time-weighted average (TLV-TWA)= 5mg/m
3
for mineral-oil mist.
National Institute for Occupational Safety and Health (NIOSH, CDC, HHS)
Recommended exposure limit (REL)= 5mg/m
3
for mineral-oil mist.
Short-term exposure limit (STEL)= 10mg/m
3
for mineral-oil mist.
Immediately dangerous to life and health (IDLH) limit= 2,500mg/m
3
for mineral-oil mist.
A comprehensive set of guidelines has been established to prevent occupational exposures to
hazardous drugs in health-care settings.
Occupational Safety and Health Administration (OSHA, Dept. of Labor)
A comprehensive set of guidelines has been established to prevent occupational exposures to
hazardous drugs in health-care settings.
References
ChemSources. 2009. Chem Sources - Chemical Search. Chemical Sources International. http://www.
chemsources.com/chemonline.html and search on mineral oil. Last accessed: 10/22/09.
HSDB. 2009. Hazardous Substances Data Bank. National Library of Medicine. http://toxnet.nlm.nih.gov/
cgi-bin/sis/htmlgen?HSDB and search on mineral oil. Last accessed: 10/22/09.
IARC. 1973. Mineral oils. In Certain Polycyclic Aromatic Hydrocarbons and Heterocyclic Compounds. IARC
Monographs on the Evaluation of Carcinogenic Risk of Chemicals to Humans, vol. 3. Lyon, France:
International Agency for Research on Cancer. pp. 30-33.
IARC. 1984. Mineral oils (lubricant base oils and derived products). In Polynuclear Aromatic Compounds,
Part 2. Carbon Blacks, Mineral Oils and Some Nitroarenes. IARC Monographs on the Evaluation of Carcinogenic
Risk of Chemicals to Humans, vol. 33. Lyon, France: International Agency for Research on Cancer. pp. 87-168.
IARC. 1987. Mineral oils: untreated and mildly-treated oils (Group 1), highly-rened oils (Group 3). In
Overall Evaluations of Carcinogenicity. IARC Monographs on the Evaluation of Carcinogenic Risk of Chemicals
to Humans, suppl. 7. Lyon, France: International Agency for Research on Cancer. pp. 252-254.
NIOSH. 1990. National Occupational Exposure Survey (1981-83). National Institute for Occupational Safety
and Health. Last updated: 7/1/90. http://www.cdc.gov/noes/noes1/m0603sic.html.
NPRA. 1981. Report on U.S. Lubricating Oil Sales. Washington, DC: National Petroleum Reners Association.
