Mineral oil

Bottle of mineral oil as sold in the U.S.

A mineral oil is any of various colorless, odorless, light mixtures of higher alkanes from a mineral source, particularly a distillate of petroleum.^[1]

The name mineral oil by itself is imprecise, having been used for many specific oils over the past few centuries. Other names, similarly imprecise, include white oil, liquid paraffin, pariffinum liquidum (Latin), and liquid petroleum. Baby oil is a perfumed mineral oil.

Most often, mineral oil is a liquid by-product of refining crude oil to make gasoline and other petroleum products. This type of mineral oil is a transparent, colorless oil composed mainly of alkanes^[2] and cycloalkanes, related to petroleum jelly. It has a density of around 0.8 g/cm³.^[3]

Mineral oil is a substance of relatively low value, and it is produced in very large quantities. Mineral oil is available in light and heavy grades, and can often be found in drug stores.

Three basic classes of mineral oils exist:

• Alkanes, based on n-alkanes
• Naphthenic oils, based on cycloalkanes
• Aromatic oils, based on aromatic hydrocarbons (distinct from essential oils)

Nomenclature

Some of the imprecision in the definition of the names (e.g., "mineral oil", "white oil") reflects usage by buyers and sellers who did not know, and usually did not need to care about, the precise chemical makeup. Prior to the late 19th century, the chemical science to determine such makeup was unavailable in any case, so the fact that one name ended up applied to various oils is unsurprising. A similar lexical situation occurred with the term "white metal".

"Mineral oil", as sold widely and cheaply in the USA, is not sold as such in Britain. Instead British pharmacologists use the terms "Paraffinum perliquidum" for light mineral oil and "Paraffinum liquidum" or "Paraffinum subliquidum" for somewhat thicker (more viscous) varieties. The term "Paraffinum Liquidum" is often seen on the ingredient lists of baby oil and cosmetics. British aromatherapists commonly use the term "white mineral oil".

Toxicology

The World Health Organization classifies untreated or mildly treated mineral oils as Group 1 carcinogens to humans; highly refined oils are classified as Group 3, meaning they are not suspected to be carcinogenic but available information is not sufficient to classify them as harmless.^[4]

The UK Food Standards Agency (FSA) carried out a risk assessment on the findings of a survey made in 2011 on risks due to migration of components from printing inks used on carton-board packaging, including mineral oils, into food. The FSA did not identify any specific food safety concerns due to inks.^[5]

People can be exposed to mineral oil mist in the workplace by breathing it in, skin contact, or eye contact. In the United States, the Occupational Safety and Health Administration has set the legal limit for mineral oil mist exposure in the workplace as 5 mg/m³ over an 8-hour workday. The National Institute for Occupational Safety and Health has set a recommended exposure limit of 5 mg/m³ over an 8-hour workday and 10 mg/m³ short term exposure. At levels of 2500 mg/m³, mineral oil mist is immediately dangerous to life and health.^[6]

Applications

Biomedicine

Cell culture

Mineral oil of special purity is often used as an overlay covering microdrops of culture medium in petri dishes, during the culture of oocytes and embryos in IVF and related procedures. The use of oil presents several advantages over the open culture system: it allows for several oocytes and embryos to be cultured simultaneously, but observed separately, in the same dish; it minimizes evaporation (therefore concentration and pH changes) of the medium; it allows for a significant reduction of the medium volume used (as few as 20 microlitres per oocyte instead of several millilitres for the batch culture); and it serves as a temperature buffer minimizing thermal shock to the cells while the dish is taken out of the incubator for observation.

Veterinary uses

Certain mineral oils are used in livestock vaccines, as an adjuvant to stimulate a cell-mediated immune response to the vaccinating agent. In the poultry industry, plain mineral oil can also be swabbed onto the feet of chickens infected with scaly mites on the shank, toes, and webs. Mineral oil suffocates these tiny parasites. In beekeeping, food grade mineral oil saturated paper napkins placed in hives are used as a treatment for tracheal and other mites. It is also used along with a cotton swab to remove un-shed skin on reptiles such as lizards and snakes.

Cosmetics

Mineral oil is a common ingredient in baby lotions, cold creams, ointments and cosmetics. It is a lightweight inexpensive oil that is odorless and tasteless. It can be used on eyelashes to prevent brittleness and breaking and, in cold cream, is also used to remove creme make-up and temporary tattoos. One of the common concerns regarding the use of mineral oil is its presence on several lists of comedogenic substances. These lists of comedogenic substances were developed many years ago and are frequently quoted in the dermatological literature.

A paper written by a cosmetic company and published in the Journal of Cosmetic Dermatology (2005) found that the type of highly refined and purified mineral oil found in cosmetic and skincare products is noncomedogenic (does not clog pores).^[7]

Mechanical, electrical and industrial

An electrical heat radiator that uses mineral oil as a heat transfer fluid

Mineral oil is used in a variety of industrial/mechanical capacities as a non-conductive coolant or thermal fluid in electric components as it does not conduct electricity, while simultaneously functioning to displace air and water. Some examples are in transformers where it is known as transformer oil, and in high voltage switchgear where mineral oil is used as an insulator and as a coolant to disperse switching arcs.^[8] The dielectric constant of mineral oil ranges from 2.3 at 50 °C to 2.1 at 200 °C.^[9]

Electric space heaters sometimes use mineral oil as a heat transfer oil. Because it is noncompressible, mineral oil is used as a hydraulic fluid in hydraulic machinery and vehicles. It is also used as a lubricant and a cutting fluid. Light mineral oil is also used in textile industries and used as a jute batching oil.

An often cited limitation of mineral oil is that it is poorly biodegradable; in some applications, vegetable oils such as cottonseed oil or rapeseed oil may be used instead.^[10]

Food preparation

Food grade mineral oil has an E number of E905a, although it is not approved in food products in the European Union, and incidental amounts in foods are carefully regulated.^[11] Because of its properties that prevent water absorption, combined with its lack of flavor and odor, food grade mineral oil is a popular preservative for wooden cutting boards, salad bowls and utensils. Rubbing a small amount of mineral oil into a wooden kitchen item periodically will prevent absorption of food odors and ease cleaning, as well as maintain the integrity of the wood, which is otherwise subjected to repeated wetting and drying in the course of use. The oil fills small surface cracks that may otherwise harbor bacteria.^[12]

Outside of the European Union, it is occasionally used in the food industry, particularly for confectionery. In this application, it is typically used for the glossy effect it produces, and to prevent the candy pieces from adhering to each other. It has been discouraged for use in children's foods,^[13] though it is still found in many confectioneries, including Swedish Fish.^[14] The use of food grade mineral oil is self-limiting because of its laxative effect. The maximum daily intake is calculated to be about 100 mg, of which some 80 mg are contributed from its use on machines in the baking industry.^[15]

It is sometimes used as a lubricant in enema preparations, because most of the ingested material is excreted in the stool rather than being absorbed by the body.^[15]

Miscellaneous

Mineral oil's ubiquity has led to its use in some niche applications as well:

Applying mineral oil to a butcher block counter top

• Used for treating and preserving wooden butcher block counter tops.^[16]

• Recommended by the American Society for Reproductive Medicine for use as a fertility-preserving vaginal lubrication.^[17]

• Commonly used to create a "wear" effect on new clay poker chips, which can otherwise be accomplished only through prolonged use. The chips are either placed in mineral oil (and left there for a short period of time), or the oil is applied to each chip individually, then rubbed clean. This removes any chalky residue left over from manufacture, and also improves the look and "feel" of the chips.^[18]

• Principal fuel in some types of gel-type scented candles.^[19]

• Liquid submersion cooling of components in some custom-built computers.^[20][21]

• Veterinarian-grade mineral oil, an inexpensive source for mineral oil, is frequently used by amateur radio operators as coolant in RF dummy loads.

• Polishing alabaster in stonework.

• Lubricating and cleaning pocket knives or food handling tools that use an open bearing, thus needing periodic lubrication.

• Inexpensive alternative for storing reactive metals (lithium, sodium, etc.).

• Horticultural oil is often made of a combination of mineral oil and detergent. It is sprayed on plants to control scale, aphid and other pest populations by suffocating the pest.

• Light mineral oil (paraffinum perliquidum) is used as a honing oil when sharpening edge tools (such as chisels) on abrasive oil stones.

• Used to overlay PCR reactions in biotechnology to prevent loss of water during heating cycles.

• Often used to suspend crystals for use in X-ray crystallography.

• Mineral oil USP or light mineral oil can be used as an anti-rust agent for blades.

• As a transparent collision material for reactions in particle physics, as in the MiniBooNE neutrino oscillation experiment.^[22]

See also

• Oil analysis
• Penetrating oil

References

External links

Wikimedia Commons has media related to Mineral oil.

• "Safety and Health Guideline for Oil Mist, Mineral Oil", Occupational Safety and Health Administration
• Lawrence Livermore National Laboratory – Safe handling of Alkali Metals
• FAO – Report on food safety of mineral oil, 1970