Benzene
C6H6
Class: Aromatic Hydrocarbons
| Chemical Name: | Molecular Makeup: |
|
Benzene |
C6H6 |
Sources: A number of aromatic hydrocarbons are derived from Benzene, including Phenol, and it is used extensively in the plastics industry, which necessitates its refinement from petroleum.[2] Benzene is also a byproduct of the combustion of materials containing carbon, including cigarettes and gasoline. The US produced 3.109 billion gallons of benzene in 2004 and averages a 4% annual increase. The three largest producers are Exxon Mobil, Equistar Chemicals LP, and Dow Chemical Company.[1] In 2004, China produced 2.5563 million tons. Most (55%) of this goes to the synthesis of styrene, which is used in the production of plastics, polyesters and elastomers.[1] The EPA reported industrial release of benzene fell from 34 million pounds in 1988 to 6.7 million pounds in 2001. [7] Natural emissions of benzene are negligible compared to anthropogenic sources. [6]
Transport Vectors: Airborne. Slightly water soluble. Very lipid soluble and carries in the lipids of aquatic organisms, but does not appear to bioaccumulate.[1][3] Cigarette consumption vastly increases exposure to benzene. [2] Despite biodegrading rapidly in air, water and soil, benzene’s constant release (6.7 million tons from industry in 2004) and high volatility provide it the capacity for transportation in significant quantities. Over 99% of benzene released goes directly into the air and that which is released into the soil and water transfer rapidly. In air, Benzene is eventually transformed either to Glyoxal, Formaldehyde and Maleic Anhydride or 2,6-Dinitrophenol. Emission and exposure sources do not necessarily coincide as demonstrated in the table below:
Emission Source: |
Emissions accounted for: |
Exposure accounted for: |
Car Exhaust |
82% |
18% |
Cigarettes |
0.1% |
40% |
Industry |
14% |
3% |
Personal Activities |
3% combined |
18% |
Home Sources (paints, etc.) |
16% |
Sample Concentration Levels
Abiotic Media:
Water |
Soil |
Air |
Cigarette Smoke |
2003-2005 |
Infrequent, found in only 9% of EPA’s 355 stations |
1975-1985 averages |
Mainstream: 5.9 to 75 μg/m3 or 1.8 to 23.6 ppb |
Biotic Media:
Fish |
Food (in ppb) |
Haddock: 100-200 ppb [1] |
Cow milk: n/a |
Human:
Blood: |
Tissue: |
Urine: |
Breastmilk: |
Decays rapidly |
0.020 - 11.70 μg g-1 [10] |
Metabolites only |
Not present |
Benzene levels remain much higher at source points such as areas of heavy traffic or homes of smokers. Benzene’s short life in human blood means only very recent, severe exposure leaves a trace in such samples. Metabolites of Benzene such as phenol can be useful in testing for Benzene exposure but only in cases where levels exceed 10 ppm.
Health effects: Benzene has been widely recognized as carcinogenic by the US Department of Health and Human Services, the EPA, the Australian Department of the Environment, Water, Heritage and the Arts and a number of other governments and organizations. [1] [4]
THRESHOLD LEVELS |
|||
EXPOSURE BY INHALATION |
SYMPTOMS |
||
ppm |
mg m-3 |
|
|
25 |
80 |
No immediate clinical effects (8 hours) |
|
50 – 150 |
160 – 480 |
Headache, lethargy, weakness (5 hours) |
|
500 |
1,600 |
Symptoms of illness (60 minutes) |
|
1,500 |
4,800 |
Serious symptoms (60 minutes) |
|
7,500 |
24,000 |
Dangerous to life (30 minutes). |
|
20,000 |
64,000 |
Fatal (5 – 10 minute exposure). |
|