Benzene

2021-09-17

Benzene is an organic chemical compound. It is composed of 6 carbon atoms in a ring, with 1 hydrogen atom attached to each carbon atom, with the molecular formula C6H6. [1] It is a chemical that is a colourless or light yellow liquid at room temperature, has a sweet odour and is highly flammable. Benzene evaporates into the air very quickly. Its vapour is heavier than air and may sink into low-lying areas. It dissolves only slightly in water and will float on top of water. [2]

Uses

Benzene is used mainly as an intermediate to make other chemicals. About 80% of benzene is consumed in the production of three chemicals, ethylbenzene, cumene, and cyclohexane. Its most widely-produced derivative is ethylbenzene, precursor to styrene, which is used to make polymers and plastics. Cumene is converted phenol for resins and adhesives. Cyclohexane is used in the manufacture of Nylon. Smaller amounts of benzene are used to make some types of rubbers, lubricants, dyes, detergents, drugs, explosives, and pesticides. [1] Benzene is used as a constituent in motor fuels; as a solvent for fats, waxes, resins, oils, inks, paints and plastics; in the extraction of oils from seeds and nuts; and in photogravure printing. [3]

Sources & Routes of Exposure [4]

The major sources of benzene exposure are tobacco smoke, automobile service stations, exhaust from motor vehicles, and industrial emissions. About 50% of the entire nationwide exposure to benzene results from smoking tobacco or from exposure to tobacco smoke. Vapours (or gases) from products that contain benzene, such as glues, paints, furniture wax, and detergents, can also be a source of exposure. Individuals employed in industries that make or use benzene may also be exposed. These industries include benzene production (petrochemicals, petroleum refining, and coke and coal chemical manufacturing), rubber tire manufacturing, and storage or transport of benzene and petroleum products containing benzene. Other workers who may be exposed to benzene because of their occupations include steel workers, printers, rubber workers, shoe makers, laboratory technicians, firefighters, and gas station employees.

Benzene enters the body through inhalation and ingestion. It is rapidly absorbed through the lungs; approximately 50% of the benzene in air is absorbed. Over 90% of ingested benzene is absorbed through the gastrointestinal tract. Absorbed benzene is rapidly distributed throughout the body and tends to accumulate in fatty tissues. The liver serves an important function in benzene metabolism, which results in the production of several reactive metabolites. At low exposure levels, benzene is rapidly metabolised and excreted predominantly as conjugated urinary metabolites. At higher exposure levels, metabolic pathways appear to become saturated and a large portion of an absorbed dose of benzene is excreted as parent compound in exhaled air.

Health Effects

Acute Effects

Co-exposure to benzene with ethanol (e.g., alcoholic beverages) can increase benzene toxicity in humans. Neurological symptoms of inhalation exposure to benzene include drowsiness, dizziness, headaches, and unconsciousness in humans. Ingestion of large amounts of benzene may result in vomiting, dizziness, and convulsions in humans. Exposure to liquid and vapour may irritate the skin, eyes, and upper respiratory tract in humans. Redness and blisters may result from dermal exposure to benzene.

Chronic Effects

Chronic inhalation of certain levels of benzene causes disorders in the blood in humans. Benzene specifically affects bone marrow (the tissues that produce blood cells). Aplastic anaemia (a risk factor for acute nonlymphocytic leukaemia), excessive bleeding, and damage to the immune system (by changes in blood levels of antibodies and loss of white blood cells) may develop. Benzene causes both structural and numerical chromosomal aberrations in humans. EPA has established an oral Reference Dose (RfD) for benzene of 0.004 milligrams per

Reproductive/Developmental Effects

There is some evidence from human epidemiological studies of reproductive and developmental toxicity of benzene; however the data do not provide conclusive evidence of a link between exposure and effect. Animal studies have provided limited evidence that exposure to benzene may affect reproductive organs; however these effects were only observed at exposure levels over the maximum tolerated dose.

Adverse effects on the foetus, including low birth weight, delayed bone formation, and bone marrow damage, have been observed where pregnant animals were exposed to benzene by inhalation.

Cancer Risk

Increased incidence of leukaemia (cancer of the tissues that form white blood cells) has been observed in humans occupationally exposed to benzene. EPA has classified benzene as a Group A, known human carcinogen.

Safety

First Aid Measures

  • Eye Contact: Check for and remove any contact lenses. In case of contact, immediately flush eyes with plenty of water for at least 15 minutes. WARM water MUST be used. Get medical attention immediately.
  • Skin Contact: In case of contact, immediately flush skin with plenty of water. Cover the irritated skin with an emollient. Remove contaminated clothing and shoes. Wash clothing before reuse. Thoroughly clean shoes before reuse. Get medical attention.
  • Serious Skin Contact: Wash with a disinfectant soap and cover the contaminated skin with an anti-bacterial cream. Seek immediate medical attention.
  • Inhalation: If inhaled, remove to fresh air. If not breathing, give artificial respiration. If breathing is difficult, give oxygen. Get medical attention if symptoms appear.
  • Serious Inhalation: Evacuate the victim to a safe area as soon as possible. Loosen tight clothing such as a collar, tie, belt or waistband. If breathing is difficult, administer oxygen. If the victim is not breathing, perform mouth-to-mouth resuscitation. Seek medical attention.
  • Ingestion: Do NOT induce vomiting unless directed to do so by medical personnel. Never give anything by mouth to an unconscious person. If large quantities of this material are swallowed, call a physician immediately. Loosen tight clothing such as a collar, tie, belt or waistband.

Exposure Controls & Personal Protection

  • Engineering Controls: Provide exhaust ventilation or other engineering controls to keep the airborne concentrations of vapours below their respective threshold limit value. Ensure that eyewash stations and safety showers are proximal to the work-station location.
  • Personal Protection: Splash goggles, lab coat, vapour respirator (be sure to use an approved/certified respirator or equivalent), gloves.
  • Personal Protection in Case of a Large Spill: Splash goggles, full suit, vapour respirator, boots, and gloves. A self contained breathing apparatus should be used to avoid inhalation of the product. Suggested protective clothing might not be sufficient; consult a specialist BEFORE handling this product.
  • Exposure Limits: TWA: 0.5 STEL: 2.5 (ppm) from ACGIH (TLV) [United States] TWA: 1.6 STEL: 8 (mg/m3) from ACGIH (TLV) [United States] TWA: 0.1 STEL: 1 from NIOSH TWA: 1 STEL: 5 (ppm) from OSHA (PEL) [United States] TWA: 10 (ppm) from OSHA (PEL) [United States] TWA: 3 (ppm) [United Kingdom (UK)] TWA: 1.6 (mg/m3) [United Kingdom (UK)] TWA: 1 (ppm) [Canada] TWA: 3.2 (mg/m3) [Canada] TWA: 0.5 (ppm) [Canada]Consult local authorities for acceptable exposure limits.

References

http://en.wikipedia.org/wiki/Benzene

http://www.bt.cdc.gov/agent/benzene/basics/facts.asp

http://www.epa.gov/ttn/atw/hlthef/benzene.html

http://www.atsdr.cdc.gov/toxguides/toxguide-3.pdf

http://www.sciencelab.com/msds.php?msdsId=9927339