Naphtha: A Hazardous Air Pollutant?

Naphtha is a broad term for flammable liquid mixtures of hydrocarbons derived from petroleum or coal tar. It is a common feedstock for producing high-octane gasoline and is used in the petrochemical and chemical industries. Naphthalene, a derivative of naphtha, is a known toxic air pollutant and possible human carcinogen. It is widely present in ambient and indoor air due to emissions from various industrial and combustion sources, including tobacco smoking and the use of mothballs, fumigants, and deodorizers. With naphthalene's potential health risks, the question arises: is naphtha, its parent compound, also a hazardous air pollutant?

Naphtha's toxicity

Naphtha is a complex mixture of hydrocarbon molecules generally containing between 5 and 12 carbon atoms. It is a volatile and flammable liquid mixture that is a distillation product of petroleum or coal tar. The toxicity of naphtha is evident in its vapour form, which can cause adverse health effects in humans.

A study observed the toxic effects of acute exposure to petroleum naphtha distillate vapours. The individuals exposed experienced dyspnea, which is difficulty in breathing, possibly due to oxygen deprivation. Some individuals also exhibited mild nausea, tremulousness, and cyanotic episodes. One person even experienced premature ventricular contractions, highlighting the severe impact on cardiac function.

The toxic effects of naphtha ingestion have also been reported, leading to acute myocardial infarction and renal failure. This underscores the serious health risks associated with naphtha exposure through inhalation and ingestion.

Naphtha is a known air pollutant and is utilised as a feedstock for producing high-octane gasoline. It is also used in the petrochemical industry for olefin production and as a solvent in the chemical industry. These applications contribute to its presence in the air and potential impact on air quality.

While naphtha itself is not listed as a hazardous air pollutant by the US EPA, the agency maintains a list of hazardous air pollutants that are regulated under the Clean Air Act. This list is subject to modifications, with pollutants being added or removed over time. Naphtha's toxicity and its presence as an air pollutant underscore the importance of managing and regulating its use and emissions to minimise potential health risks to humans and the environment.

Naphtha's carcinogenic properties

Naphtha is a broad term for a number of different flammable liquid mixtures of hydrocarbons. It is a distillation product from petroleum or coal tar, boiling within a certain range and containing specific hydrocarbons. Full-range naphtha, which boils between 30°C and 200°C, is a complex mixture of hydrocarbon molecules with 5-12 carbon atoms. Light naphtha, boiling between 30°C and 90°C, and heavy naphtha, boiling between 90°C and 200°C, are subsets of full-range naphtha.

Naphtha is a common component of crude oil, typically constituting 15-30% of its weight. It is used as a feedstock for producing high-octane gasoline and in the petrochemical industry for olefin production. Naphtha is also used in the chemical industry as a solvent, with applications including lighter fluid, camp stove fuel, and cleaning solvents.

While naphtha is a known air pollutant, there is no evidence to suggest that petroleum-derived distillates are carcinogenic in humans. However, workers exposed to naphtha, specifically VM&P naphtha (also known as light naphtha and spotting naphtha), in inadequately ventilated buildings have exhibited symptoms of intoxication with aliphatic compounds. These symptoms include lightheadedness, labored breathing, tremors, hyperactivity, and nausea.

Despite the lack of direct evidence for carcinogenicity, certain naphthalene derivatives have been synthesised and exhibit significant antimicrobial action. Additionally, some naphthalene-containing molecules have demonstrated antitumor activity, and naphthalimides have been synthesised as potential anticancer agents. These compounds have been evaluated for their cytotoxic activity against HeLa cells, and their DNA intercalation properties have been established.

Naphtha's presence in ambient and indoor air

Naphtha is a broad term for a number of flammable liquid mixtures of hydrocarbons, which are a distillation product of petroleum or coal tar. It is a complex mixture of hydrocarbon molecules, generally with between 5 and 12 carbon atoms. Naphtha is a hazardous air pollutant and is regulated by the EPA under the Clean Air Act.

Naphtha is present in both ambient and indoor air, though the concentration and specific type (light or heavy) may vary depending on the location and source. In ambient air, naphtha can be released into the atmosphere through a variety of industrial processes and activities, including the production and use of petroleum products, such as gasoline, diesel, and kerosene. Ambient air concentrations of naphtha can be particularly high in industrial areas, where it is emitted from refineries, chemical plants, and other facilities that use or produce petroleum products.

Naphtha can also be found in indoor air, particularly in spaces where petroleum products are used or stored, such as garages, workshops, and storage closets. Indoor air concentrations of naphtha can be influenced by a variety of factors, including ventilation, the presence of petroleum-based products, and even the use of certain household chemicals and cleaning products. For example, the use of lighter fluid, camp stove fuel, and some cleaning solvents can all release naphtha into indoor air.

The presence of naphtha in ambient and indoor air can pose health risks to humans, as it is a known carcinogen and can also cause eye, nose, and throat irritation, as well as headaches, dizziness, and nausea. Prolonged exposure to high concentrations of naphtha in ambient or indoor air can also result in more severe health effects, including damage to the central nervous system and respiratory system.

To minimise the presence of naphtha in indoor air, it is important to ensure adequate ventilation and to avoid using petroleum-based products or storing them in enclosed spaces. In industrial settings, regulations and emissions controls are often in place to limit naphtha emissions into the ambient air, though further efforts are needed to reduce the potential health risks associated with this hazardous air pollutant.

Industries that use naphtha

Naphtha is a highly versatile substance with a wide range of applications across various industries. It is a colourless liquid with a similar odour to gasoline and is highly flammable.

One of the major uses of naphtha is as a feedstock for the production of high-octane gasoline through a catalytic reforming process. It is also used in the synthesis of ethylene and propylene, which are monomers for different polymers. Naphtha is essential in the production of plastics and polymer synthesis, as well as in the creation of synthetic fibres such as polyester and nylon for the textile industry.

Naphtha is also used as a solvent in cleaning products, paints, varnishes, and asphalt. Its low evaporation rate makes it suitable for these applications. Additionally, it is used in the pharmaceutical industry as a starting material for the synthesis of active pharmaceutical ingredients (APIs) and various drugs.

In the energy industry, power plants and industrial burners use naphtha as fuel due to its high energy density. It is particularly useful in situations where other fuels may not be as effective. Naphtha is also crucial for refining operations that produce gasoline, helping to meet the global demand for transportation fuels.

Naphtha has historically been used for crude oil and diesel fuel in some countries, although these usages are now mostly obsolete.

Regulations on hazardous air pollutants

Naphtha is a complex mixture of hydrocarbon molecules generally having between 5 and 12 carbon atoms. It is a flammable liquid mixture of hydrocarbons derived from petroleum or coal tar. While I cannot find explicit information on whether naphtha is a hazardous air pollutant, the US Environmental Protection Agency (EPA) does provide information on hazardous air pollutants and their regulations.

The Clean Air Act (CAA) requires the EPA to regulate emissions of hazardous air pollutants, also known as air toxics, from industrial sources. The EPA must also regulate emissions from stationary sources, which are defined as any stationary source or group of stationary sources that emit or have the potential to emit 10 tons per year or more of any hazardous air pollutant or 25 tons per year or more of any combination of hazardous air pollutants.

The EPA's approach to understanding and regulating hazardous air pollutants involves listing categories or subcategories of area sources that present a threat to human health or the environment. The EPA then develops regulatory programs to limit emissions from these sources. The National Emissions Standards for Hazardous Air Pollutants (NESHAPs) provide an alphabetical list of hazardous air pollutants by source category, including area sources.

The CAA also mandates controls on air pollution from mobile sources, such as motor vehicles and nonroad engines, by regulating both the composition of fuels and emission-control components. Vehicle fuel standards are met by refiners/importers and other parties in the fuel distribution system. The EPA also sets protective limits on emissions and informs people about radiation and radiation hazards.

The list of hazardous air pollutants is subject to change, with substances being added or removed over time. For example, 1-bromopropane was added to the list in 2022, while methyl ethyl ketone, ethylene glycol monobutyl ether, caprolactam, and surfactant alcohol ethoxylates and their derivatives have been removed.

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