Benzene

Primary reference(s)

WHO, 2019. Preventing disease through healthy environments: Exposure to benzene: a major public health concern. World Health Organization (WHO). Accessed 19 November 2019.

Additional scientific description

Benzene is a stable colourless liquid at room temperature and normal atmospheric pressure. Benzene melts at 5.5°C and boils at 80.1°C; and has a characteristic aromatic odour. It has a high vapour pressure, which causes it to evaporate rapidly at room temperature, and is highly flammable. It is slightly soluble in water but miscible with most other organic solvents (IPCS, 1993).

Benzene is used as a solvent in the chemical and pharmaceutical industries. It also occurs naturally in petroleum products (e.g., crude oil and gasoline) at levels up to 4 g/l. The primary route of benzene exposure and subsequent toxicity is via inhalation. The highest exposures have typically been in the workplace – for example, in industries that make or use benzene. The general population may be exposed through the inhalation of contaminated air, particularly in areas of heavy automobile traffic, gas stations and areas near industrial sources. Other sources include cigarette smoking, second-hand smoke, off-gassing from building material and structural fires. People also may be exposed to benzene in contaminated drinking water and some foods (American Cancer Society, 2016; WHO, 2019).

The compulsory introduction of catalytic converters on car exhausts and legislation to reduce benzene levels in car fuels has contributed to a reduction of benzene emissions. Other interventions to prevent or reduce exposures to airborne benzene include promoting the use of alternative solvents in industrial processes, developing and implementing policies and legislation to remove benzene from consumer products, discouraging domestic use of benzene-containing products, promoting building codes requiring detached garages, and implementing the World Health Organization (WHO) Framework Convention on Tobacco Control (WHO, 2003), including providing for protection from exposure to tobacco smoke in workplaces and public areas (WHO, no date).

Metrics and numeric limits

Drinking-water: The WHO guideline value for benzene is 0.01 mg/l. This is based on extrapolation of modelled excess lifetime risk for leukaemia from epidemiological studies involving inhalation exposure; guideline values corresponding to modelled excess lifetime cancer risks* of 10-4, 10-5 and 10-6 are 0.1, 0.01 and 0.001 mg/l, respectively (WHO, 2019).

*An excess lifetime cancer risk of 10-4, 10-5 or 10-6 means the risk of one new cancer case above background levels per 10,000, 100,000 or 1 million people, respectively.

Air: No specific WHO guideline value has been developed for benzene in air. Benzene is carcinogenic to humans and no safe level of exposure can be recommended. For general guidance, the concentrations of airborne benzene associated with an excess lifetime risk of leukaemia of 10-4, 10-5 and 10-6 are 17, 1.7 and 0.17 μg/m3, respectively (WHO, 2019).

Examples of drivers, outcomes and risk management

Benzene causes a range of acute effects such as acute occupational exposure to benzene which may cause narcosis: headache, dizziness, drowsiness, confusion, tremors and loss of consciousness (use of alcohol enhances the toxic effect). It is also irritating to the eyes, skin and respiratory tract (WHO, 2019).

Benzene is a well-established cause of cancer in humans. The International Agency for Research on Cancer (IARC) has classified benzene as carcinogenic to humans (Group 1). The evidence in humans is considered sufficient for acute non-lymphocytic leukaemia, including acute myeloid leukaemia, while the evidence in humans is limited for non-Hodgkin lymphoma, chronic lymphoid leukaemia, multiple myeloma, chronic myeloid leukaemia, acute myeloid leukaemia in children, and lung cancer (WHO, 2019).

The WHO factsheet on Preventing disease through healthy environments - exposure to Benzene: a major public health concern (WHO, 2019) includes the following risk mitigation recommendations:

Eliminate use:

• Promote the use of alternative solvents in industrial processes, glues and paints.
• Develop and implement policies and legislation to remove benzene from consumer products.

Reduce exposure

• Reduce exposure at petrol filling stations as far as possible by following best practice in location, design and extraction.
• Minimise emissions from vehicle exhausts by improved design and regular monitoring of engine settings.
• Separate dwelling spaces from areas where vehicles and benzene-containing products are kept. In particular, isolate children from indoor exposure to vehicle emissions.
• Avoid domestic use of benzene-containing products.
• Discourage indoor use of unflued oil and gasoline heating.
• Implement the WHO Framework Convention on Tobacco Control (WHO, 2003), including providing for protection from exposure to tobacco smoke in indoor workplaces, public transport, indoor public places and, as appropriate, other public places.

Education

• Raise public awareness regarding sources of exposure to benzene – especially exposure through smoking – and awareness of risk mitigation measures.
• Conduct educational activities to discourage the use of benzene or petrol for cleaning and degreasing in industry, including in the informal sector.