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Benzene

//Benzene

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 of Emission & Routes of Exposure

 

Sources of Emission [4]

 

  • Industry sources: Releases to air from industries producing, using or handling benzene eg. rubber industry, oil refineries, chemical plants, footwear manufacturing, petrol.
  • Diffuse sources: Present in crude oil; cigarette smoke (will affect both active and passive smokers). Releases to air from service stations; evaporation of fuels during petrol refilling; releases to groundwater from underground storage tanks that leak.
  • Natural sources: Occurs naturally in volcanoes, forest fires, some plants and animals. Is present in crude oil.
  • Transport sources: Vehicle exhaust, Evaporation of vehicle fuels from motors and vehicle fuel tanks.
  • Consumer products: Glues, adhesives, household cleaning products, paint strippers, some art supplies and petrol. These products may contain benzene as a contaminant rather than a deliberately added component (e.g. Shellite may contain 0.1% benzene by volume).

 

Routes of Exposure [5]

 

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.

Inhalation is the primary route of exposure for general and occupational populations. With oral and derma; being minor routes of exposure.

 

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.

 

Regulation

 

United States [7]

 

Exposure LimitLimit ValuesHE CodesHealth Factors and Target Organs
OSHA Permissible Exposure Limit (PEL) – General IndustrySee29 CFR 1910.10281 ppmTWA
5 ppm
STEL		HE1Leukaemia
HE7Central nervous system excitation followed by central nervous system depression
HE8Loss of consciousness, respiratory paralysis, death (very high concentrations)
HE12Nonmalignant blood disorders (bleeding, anaemia, aplastic anaemia, thrombocytopenia, leukopenia)
HE14Eye, nose, and respiratory irritation
OSHA PEL–Sectors Excluded from General Industry
See1910.1000 Table Z-2(See also Z37.40-1969)

Note: These values apply to the industry segments exempt from the 1 ppm 8-hour TWA and 5 ppm STEL of the benzene standard at1910.1028.

10 ppmTWA

25 ppmCeiling

50 ppm Maximum peak above ceiling (10 minutes)

HE12Blood disorders (anaemia, leukopenia, aplastic anaemia)
HE14Eye, nose, and respiratory irritation
OSHA PEL – Construction Industry
See29 CFR 1926.1128		1 ppmTWA

5 ppm STEL

HE1Leukaemia
HE7Central nervous system excitation followed by central nervous system depression
HE8Loss of consciousness, respiratory paralysis, death (very high concentrations)
HE12Nonmalignant blood disorders (bleeding, anaemia, aplastic anaemia, thrombocytopenia, leukopenia)
HE14Eye, nose, and respiratory irritation
OSHA PEL – Shipyard Employment
See29 CFR 1915.1028		1 ppmTWA

5 ppmSTEL

HE1Leukaemia
HE7Central nervous system excitation followed by central nervous system depression
HE8Loss of consciousness, respiratory paralysis, death (very high concentrations)
HE12Nonmalignant blood disorders (bleeding, anaemia, aplastic anaemia, thrombocytopenia, leukopenia)
HE14Eye, nose, and respiratory irritation
National Institute for Occupational Safety and Health (NIOSH) Recommended Exposure Limit (REL)0.1 ppmTWA

1 ppm STEL

Ca

HE1Leukaemia
HE4Gastrointestinal irritation and anorexia; cardiac sensitisation
HE7Central nervous system depression; convulsions and paralysis; polyneuritis
HE11Pulmonary oedema, pneumonia
HE12Bone marrow damage, aplastic anaemia
HE14Eye, mucous membrane, and skin irritation; dermatitis
American Conference of Governmental Industrial Hygienists (ACGIH) Threshold Limit Value (TLV) (2001)0.5 ppm (1.6 mg/m3) TWA

2.5 ppm (8 mg/m3) STEL

A1; Skin; BEI

HE1Leukaemia, including acute myelogenous leukaemia
CAL/OSHA PELs
(See also Section 5218)		1 ppm TWA

5 ppm STEL

Skin

 

Australia [4,8]

 

Safe Work Australia: Safe Work Australia has set a time weighted average (TWA) concentration for benzene of 1 ppm or 3.2mg/m3. It has also been classified category carc. 1A.

 

Australian Drinking Water Guidelines (NHMRC and ARMCANZ , 1996):

Maximum of 0.001 mg/L (i.e. 0.000001 g/L)

 

References

  1. http://en.wikipedia.org/wiki/Benzene
  2. http://www.bt.cdc.gov/agent/benzene/basics/facts.asp
  3. http://www.epa.gov/ttn/atw/hlthef/benzene.html
  4. http://www.npi.gov.au/resource/benzene-0
  5. http://www.atsdr.cdc.gov/toxguides/toxguide-3.pdf
  6. http://www.sciencelab.com/msds.php?msdsId=9927339
  7. https://www.osha.gov/dts/chemicalsampling/data/CH_220100.html
  8. https://www.osha.gov/dts/chemicalsampling/data/CH_220100.html