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- Benzene Series (Part B)
Benzene Series (Part B)
- Posted in Default
- By admin
- Date April 23rd, 2012 18:29
Long-term exposure to benzene primarily impacts the bloodstream. Over time, benzene exposure depletes red blood cells (leading to anemia) and bone marrow weakens. Benzene exposure can cause excessive bleeding which weakens the immune system and increases the risk of infection. Long-term exposure to high levels of airborne benzene can cause leukemia, particularly acute myelogenous leukemia, often referred to as AML. The International Agency for Research on Cancer (IARC) and the United States Environmental Protection Agency (EPA) have both determined that benzene is carcinogenic to humans. Benzene is created when benzoic acid (a preservative) loses its carbon atoms (decarboxylation) in the presence of Vitamin C (ascorbic acid). Heat and light conditions can be manipulated to optimize the decarboxylation process.
Ambient outdoor air contains low levels of benzene from tobacco smoke, gas stations, car exhaust, and industrial emissions. Products containing benzene emit concentrated vapors which dissipate over time. Common sources of benzene in buildings include glues, paints, furniture waxes, and detergents. Air around hazardous waste sites and gas stations also contain concentrated levels of benzene vapors. Benzene is also a common additive to gasoline as it increases fuel octane ratings which can reduce engine knocking (ignition from combustion rather than spark plugs). Prior to the 1950s, benzene content in gasoline commonly hovered between 0.5 and 30%. Tetraethyl lead eventually replaced benzene as the most widely-used antilock additive. Following the global phaseout of leaded gasoline, benzene made a comeback and is again used as an additive to gasoline in some countries. Upon reentry into the market, concern over the negative health effects of benzene and the potential for gasoline to enter groundwater sources led to stringent regulations in the US and Europe limiting benzene content to a maximum of 1%. In 2011, US EPA released new petrol regulations further reducing benzene content to 0.62% . Prior to the 1920's, benzene was frequently used as an industrial solvent, especially for degreasing metals. As it toxicity became obvious, benzene was replaced by other solvents, especially toluene (methyl benzene) which has similar physical properties but is less carcinogenic.
Several authorities have set benzene limits for drinking water. The following limits are given in parts per billion (ppb; μg/kg). The US EPA and Californian Authorities have set public health goals limiting benzene content to 0.0 ppb and 0.15 ppb, respectively).
Benzene has also been measured in soft drinks. The worse example, to date, registered 87.9 ppb of benzene. Drinking a standard 350ml can of this soft drink would also include 31 μg (micrograms) of benzene, nearly equivalent to the benzene inhaled by a motorist refilling a fuel tank for three minutes. Though most soft drinks register much lower levels of benzene, they remain as a small but avoidable risk of exposure. For most people this will have little impact, though spread over the millions of soft drink connoisseurs, statistically there should be a few cases of cancer caused by this exposure. Compared to simply breathing, benzene exposure from soft drinks is far less dangerous. The UK Food Standards Agency has stated that the benzene inhaled over 24 hours of breathing (in London) is equivalent to drinking 20 liters (5.5 gallons) of soft drinks. The upshot: we need to regenerate the air in our cities and identify easy sources of benzene that can be removed.
As a consumer, be on the lookout for all benzene series chemicals: benzene, toluene, and xylene. Common culprits are paints and stains (interior and exterior) and plastics. Since 2001, China's Ministry of Health has set 0.087 mg/m3 as the upper safe limit for benzene content in indoor air . Measuring air quality is fairly simple. For more information on air quality in China:
to be continued...
【1】 Control of Hazardous Air Pollutants From Mobile Sources. U.S. Environmental Protection Agency. 2006-03-29: 15853
【2】LK Gardner, GD Lawrence, Benzene Production from Decarboxylation of Benzoic Acid in the Presence of Ascorbic Acid and a Transition-Metal Catalyst, Journal of Agricultural and Food Chemistry, May 1993, Volume 41, Number 5.
【3】New Zealand Food Safety Authority / Te Pou Oranga kai O Aotearoa.
【4】Indoor air quality health standards  No.255