Benzene Pollution: Naphtha's Toxic Trail

Naphtha is an intermediate hydrocarbon liquid stream derived from refining crude oil. It is desulfurized and catalytically reformed, which restructures the hydrocarbon molecules and breaks some into smaller molecules. One of the products of this process is benzene, a clear, colourless, highly flammable liquid with a characteristic odour. Benzene is a pollutant that can be found in the air, water, and soil. It is a major component of tobacco smoke, vehicle exhaust, and industrial emissions. People can be exposed to benzene through inhalation, skin contact, or ingestion, which can lead to health issues such as drowsiness, headaches, dizziness, skin irritation, and increased risk of leukemia.

Naphtha's role in benzene pollution

Naphtha is a general term for a mixture of many different hydrocarbon compounds derived from the refining of crude oil. It can also be produced from other materials such as coal tar, shale deposits, tar sands, and the destructive distillation of wood. Naphtha is primarily used as a component of gasoline or petrol.

Naphtha is composed of molecules with six or fewer carbon atoms. When these molecules are reformed, they tend to form butane and lower molecular weight hydrocarbons that are not useful as high-octane gasoline blending components. However, molecules with six carbon atoms can form aromatics, including benzene.

Benzene is a highly flammable, colourless liquid with a distinct odour. It is one of the most widely used chemicals in the United States and is commonly found in industrial emissions, tobacco smoke, and vehicle exhaust. Benzene is also present in various consumer products, including gasoline, glues, cleaning products, and paint thinners.

The presence of benzene in naphtha can contribute to air and water pollution. While naphtha itself can be an air pollutant, its reformation and use in gasoline production can release benzene into the environment. Benzene pollution can have significant health impacts, including short-term symptoms such as drowsiness, headaches, and dizziness, as well as long-term effects like an increased risk of leukaemia, anaemia, and immune system weaknesses.

To mitigate the environmental and health risks associated with benzene pollution from naphtha, regulatory measures have been implemented. Environmental regulations in several countries limit the amount of aromatics, particularly benzene, allowed in gasoline. Additionally, organisations like the Occupational Safety and Health Administration (OSHA) and the National Institute for Occupational Safety and Health (NIOSH) have set exposure limits for naphtha and benzene in workplace settings.

Naphtha's chemical composition

Naphtha is a general term for a petroleum distillate that contains a variety of hydrocarbon compounds, including paraffins, naphthenes (cyclic paraffins), and aromatic hydrocarbons. It is derived from the refining of crude oil and has a unique composition depending on the source of the oil and the refinery producing it. Naphtha has an initial boiling point (IBP) of about 35 °C and a final boiling point (FBP) of approximately 200 °C.

The crude oil distillation unit in a petroleum refinery produces the overhead liquid distillate known as virgin or straight-run naphtha, which is the primary source of naphtha in most refineries. This virgin naphtha is often further distilled into two streams: light naphtha and heavy naphtha. Light naphtha contains hydrocarbons with six or fewer carbon atoms, while heavy naphtha contains those with more than six carbon atoms. These molecules with six carbon atoms can form aromatics, including benzene, which is undesirable due to environmental regulations limiting their presence in gasoline.

Specialty naphthas, such as petroleum ether, mineral spirits, and benzine, are also available and are used in various industrial processes. These specialty naphthas undergo purification processes to adjust their chemical characteristics for specific applications. The compositional characteristics of specialty naphthas can be found on Safety Data Sheets (SDS) provided by chemical suppliers.

Naphtha is a versatile product used as a feedstock in the petrochemicals industry for the production of hydrogen, ethylene, and other olefins. It is also derived from other materials like coal tar, shale deposits, and the destructive distillation of wood, resulting in different types of naphtha with distinct chemical compositions.

Benzene's volatility and health risks

Benzene is a clear, colourless, volatile, highly flammable liquid with a distinctive odour. It has a relatively low boiling point of 80.1 °C and a high vapour pressure, causing it to evaporate quickly at room temperature. It is slightly soluble in water and can be found in the air, predominantly in the vapour phase.

The volatility of benzene is a cause for concern due to its health risks. Benzene is hazardous to human health, particularly through inhalation. The Occupational Safety and Health Administration (OSHA) has set a permissible exposure limit of 500 ppm (2000 mg/m3) over an 8-hour workday. Exposure to very high levels of benzene for a short period can have different health impacts than breathing high levels for an extended period. Short-term exposure to low levels of benzene typically does not result in immediate or severe health issues. However, some individuals may experience lung irritation, coughing, dizziness, or headaches.

Prolonged exposure to high levels of benzene can lead to excessive bleeding, affect the immune system, and increase the likelihood of infections and cancers, including leukaemia. The Colorado Air Quality Control Commission has recognised benzene as one of five priority air toxics, emphasising the significance of reducing exposure to mitigate health risks.

Benzene pollution can come from various sources, including petroleum naphtha, a general term for a mixture of hydrocarbon compounds derived from refining crude oil. Naphthas can also be produced from other materials such as coal tar, shale deposits, and tar sands. The molecules in naphtha with six carbon atoms tend to form aromatics, including benzene, which is undesirable due to environmental regulations limiting their presence in gasoline.

Indoor benzene pollution can arise from outdoor sources and indoor activities such as cooking with kerosene stoves, using building materials and furniture, heating systems, stored solvents, and various human activities. The use of fuels like coal, wood, gas, and kerosene for space heating and cooking contributes to higher benzene concentrations indoors. Tobacco smoke, paint, cleaning supplies, oil and gas operations, wildfires, and vehicle exhaust also release benzene into the air.

Sources of benzene exposure

Benzene is a clear, colourless, volatile, highly flammable liquid with a distinct odour. It is slightly soluble in water and evaporates rapidly at room temperature. Benzene exposure is a major health concern, as it is a known carcinogen and can cause serious health issues, including increasing the risk of leukaemia and other blood disorders. Here are the primary sources of benzene exposure:

Cigarette Smoke

Mainstream cigarette smoke is a significant source of benzene exposure, with smoking accounting for about 90% of benzene exposure among smokers. Environmental tobacco smoke, or secondhand smoke, is also an important contributor, making up around 5% of total nationwide exposure.

Industrial Emissions and Pollutants

Industrial emissions from factories, refineries, and petrochemical manufacturing contribute to outdoor air pollution with benzene. People working in industries that produce or use benzene may be exposed to the highest levels. The use of fuels such as coal, wood, gas, kerosene, or liquid petroleum gas (LPG) for space heating and cooking can also lead to higher indoor concentrations of benzene.

Vehicle Exhaust and Transportation

Motor vehicle exhaust emissions are a source of benzene pollution, particularly in indoor spaces like attached garages. Driving and other transportation activities contribute to personal exposure to benzene.

Building Materials and Solvents

Benzene can be released from building materials, paints, adhesives, glues, and solvents used in construction and home improvement. These products can off-gas benzene, leading to indoor air pollution.

Hazardous Waste and Gasoline Leaks

The air around hazardous waste sites, underground storage tanks, and gas stations can have higher levels of benzene. Leaks from these sources can contaminate well water, leading to indirect exposure through drinking water.

It is important to note that while these are significant sources of benzene exposure, the specific risks can vary based on duration and level of exposure, as well as individual factors. Reducing exposure to these sources, especially in indoor environments, is crucial to mitigating the health risks associated with benzene.

Benzene's presence in gasoline

Benzene is a colourless, highly flammable liquid with a sweet smell. It is a natural constituent of petroleum and is one of the elementary petrochemicals. It is also a natural part of crude oil, gasoline, and cigarette smoke.

As a gasoline (petrol) additive, benzene increases the octane rating and reduces knocking. Before the 1950s, gasoline often contained several percent of benzene. However, with the global phase-out of leaded gasoline, benzene has made a comeback as a gasoline additive in some nations. Due to its toxicity, benzene finds limited use in consumer items. In the United States, there are stringent regulations on gasoline's benzene content, with limits typically around 1%. European petrol specifications now contain the same 1% limit on benzene content.

Benzene is a Group 1 carcinogen that has been strongly linked to both occupational and non-occupational leukaemias. It targets the liver, kidney, lung, heart, and brain and can cause DNA strand breaks and chromosomal damage. It can also cause bone marrow to stop producing enough red blood cells, leading to anaemia. Long-term exposure to benzene can also affect the blood and increase the chance of infection.

Human exposure to benzene is a global health problem due to its ubiquitous presence in gasoline and hydrocarbon fuels. The major sources of benzene exposure are tobacco smoke, automobile service stations, exhaust from motor vehicles, and industrial emissions. The air around hazardous waste sites or gas stations can contain higher levels of benzene than other areas.

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