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- Benzene Series (Part C)
Benzene Series (Part C)
- Posted in Default
- By admin
- Date May 22nd, 2012 13:59
In the 1920's, benzene was frequently used as an industrial solvent. As its toxicity gradually became known, its role as a solvent was replaced by other chemicals such as Toluene, Ethylbenzene and Xylenes (with similar physical properties but very little carcinogenic potential).【1】 BTEX (Benzene, Toluene, Ethylbenzene and Xylenes) are made up of naturally-occurring chemicals that are found mainly in petroleum products such as gasoline. Refineries will change the amounts of these chemical compounds to meet vapor pressure and octane standards for gasoline. Besides gasoline, BTEX can be found in many common household products we use every day.
Toluene (one hydrogen atom of the benzene ring is replaced by a methyl group in toluene) occurs naturally as a component of many petroleum products. Toluene is used as a solvent for paints, coatings, gums, oils, and resins. Ethylbenzene (one hydrogen atom of the benzene ring is replaced by an ethyl group in ethylbenzene）is used mostly as a gasoline and aviation fuel additive. It may also be present in consumer products such as paints, inks, plastics and pesticides.
Although there are six carbon atoms in a benzene ring, they are all equal chemically, as their symmetry suggests. Xylene is di-substituted benzene, having two methyl groups replacing two hydrogen atoms. There are actually three different types or isomers of xylene.
Xylenes are used in gasoline and as a solvent in printing, rubber and leather industries. BTEX chemicals are all volatile organic compounds (VOCs). VOC chemicals easily vaporize or change from a liquid to a vapor (gas). VOC vapors can travel through the air and/or move through contaminated groundwater and soils as vapors, possibly impacting indoor air quality in
nearby homes or businesses.
Most people are exposed to small amounts of BTEX compounds in the ambient (outdoor) air, at work and in the home. Most everyone is exposed to low levels of these chemicals in their everyday activities. People who live in urban areas (cities) or by major roads and highways will likely be exposed to more BTEX than people living in rural (country) areas.
Besides common everyday exposures, larger amounts of BTEX can enter the environment when underground storage tanks leak or overflow, fuel spills or from landfills. BTEX compounds easily move through soils and can make their way into the groundwater, contaminating public and private water systems and the soils in between.
Exposure can occur by either drinking contaminated water (ingestion), by breathing contaminated air from pumping gas or from the water via showering or laundering (inhalation) or from spills on your skin (dermal). How does BTEX affect health? Acute (short-term) exposure to gasoline and its components benzene, toluene and xylenes has been associated with skin and sensory irritation, central nervous system-CNS problems (tiredness, dizziness, headache, loss of coordination) and respiratory system (eye and nose) irritation. On top of skin, sensory and CNS problems, prolonged exposure to these compounds can also degrade the kidneys, liver and blood systems.【3】
In the absence of data on the cancer-causing nature of all BTEX chemicals, possible health exposure hazards are assessed using an individual component-based approach for each individual chemical.
BTEX chemicals have similar structures though with different toxicity. Alkyl/ethyl groups are usually fairly resistant to oxidation. However, when they are attached to a benzene ring, they are oxidized. This is why Toluene, Ethylbenzene and Xylenes are very little carcinogenic potential than Benzene.
Ortho-xylene is the only naturally-occurring form of xylene; the other two forms are man-made. Para-xylene was made famous in China from the PX leaks in 2007 and 2011. Chinese citizens living in Xiamen and Dalian forced the PX plants to relocate despite the fact that PX does not have the same list of hazards as benzene. In this case, the factory closure was made not due to actual risk, rather to perceived risk. This is important to note.
We should not only focus on the toxicity of chemicals (Para-xylene, in this case). It is also critical that local governments and chemical factories have performed their responsibilities well. This includes disclosing chemical hazards to the public. In the absence of transparent information, factories should be shut down, regardless of actual risks. Unknowns are far too dangerous when it comes to chemistry. More transparency and communication are urgently needed for the chemical industry to continue to
grow and support a healthy future.【5】
How can families reduce the risk of exposure to BTEX?
● Use adequate ventilation to reduce exposure to indoor BTEX sources
● Avoid direct BTEX vapors from consumer products such as gasoline, pesticides, varnishes, paints, resins-glues and newly installed carpeting.
● Household chemicals should be stored out of reach of children to prevent accidental poisoning. Always store household chemicals in their original containers; never store them in containers that children would find attractive to eat or drink from, such as old soda bottles. Gasoline should be stored in a gasoline can with a locked cap.
● Volatile chemicals should be stored outside the home if possible – in a separate garage or shed.
● Don’t smoke indoors with doors and windows closed (or better yet, don’t smoke at all).【3】