Benzene: From Coal Tar Wonder Chemical to Leukemia Cause

Benzene smells pleasant. That was part of the problem.

In the 19th century, it was used as an aftershave and a perfume solvent. Workers in early industrial settings — rubber factories, shoe manufacturing, printing, petroleum refining — were bathed in it for hours each day. It was pleasant enough that they didn't object.

The haematological effects appeared gradually: anaemia, thrombocytopenia, then aplastic anaemia, then leukaemia. The connection between benzene exposure and blood disease was suspected by European physicians from the 1880s, confirmed by Italian researchers in the 1920s, and formally established in American workers in the 1970s — nearly a century after the first clinical observations.

During those intervening decades, the American petroleum and rubber industries, which depended on benzene as both a raw material and a processing solvent, built a comprehensive infrastructure of funded research, lobbying, and regulatory delay that is as well-documented as any in the history of industrial toxicology. The story of benzene's OSHA standard is a case study in how industry can manipulate the regulatory process — and in how scientists can fight back.

The occupational leukaemia evidence that drove the benzene regulatory debate came from a specific group of workers in a specific plant: rubber workers in the Pliofilm manufacturing plant in Ohio, studied by Robert Rinsky and colleagues at NIOSH.

Pliofilm was a rubber-like material used in food packaging, manufactured using benzene as a solvent. Workers at the Ohio plants had substantial benzene exposure over decades. Rinsky's analysis found a striking dose-response relationship between estimated cumulative benzene exposure and leukaemia mortality — workers with the highest estimated exposures had leukaemia rates far above the expected population baseline.

The exposure-response relationship The Pliofilm study provided the exposure-response data that OSHA used to justify its proposed 1 ppm standard for workplace benzene in 1977. The existing standard was 10 ppm. Industry challenged the proposed reduction to 1 ppm in court, arguing that OSHA had not demonstrated that workers were at significant risk at 10 ppm.

The Supreme Court decision In 1980, the Supreme Court's Industrial Union Department v. American Petroleum Institute (the "benzene case") overturned the 1 ppm standard, ruling that OSHA had not quantified the risk at the existing 10 ppm standard before demonstrating a benefit from the stricter rule. The decision remanded the issue to OSHA and set a precedent for the quantitative risk assessment requirement that has shaped regulatory toxicology ever since.

OSHA eventually promulgated the 1 ppm standard in 1987, after a decade of additional analysis and industry opposition, using the Pliofilm data as the quantitative foundation.

The OSHA benzene standard battle established the legal and procedural framework for chemical risk regulation in the US — and the strategies that delayed it have been deployed repeatedly in subsequent regulatory fights.

The regulatory delay playbook: 1. Contest the scientific evidence (fund alternative analyses; challenge peer-reviewed findings) 2. Challenge the legal authority (argue that OSHA lacks authority for the proposed standard) 3. Demand more data (claim existing evidence is insufficient; argue for further study before action) 4. Challenge the risk assessment methodology (dispute dose-response models, extrapolation from high to low doses) 5. Argue economic infeasibility (claim the standard would devastate the industry)

These tactics were used against benzene regulation in the 1970s–1980s. They were used against leaded gasoline regulation. Against asbestos regulation. Against PFAS regulation. And they are being used today against emerging chemical regulations.

The NIOSH scientists' integrity What the benzene story also illustrates is the importance of scientists who maintain their independence under industry pressure. Robert Rinsky's Pliofilm work, and the work of researchers at academic institutions and government agencies who continued building the benzene evidence base despite industry opposition, ultimately provided the scientific foundation that regulation required.

The benzene regulatory history is one reason why the IARC classification system — which operates independently of regulatory or industry influence — is so important as a scientific reference point.

Benzene exposure today is not limited to industrial settings. Several contemporary exposure sources are relevant to the general population.

Tobacco smoke The single largest benzene exposure source for most smokers. A cigarette contains approximately 20–40 µg of benzene; smokers have urinary benzene metabolite concentrations roughly 10 times higher than non-smokers. Environmental tobacco smoke (secondhand smoke) is also a significant benzene source for non-smokers in smoking environments.

Gasoline and vehicle traffic Benzene is a natural component of petroleum and is present in gasoline at approximately 1%. Refuelling a car involves direct benzene inhalation. Living near petrol stations or in high-traffic areas involves chronic low-level benzene exposure from vehicle exhaust, though the catalytic converter has dramatically reduced exhaust benzene concentrations since the 1970s.

Scented candles Some scented candles, particularly those with petroleum-derived paraffin wax, release detectable benzene levels when burned. The IARC classification of benzene as a Group 1 carcinogen makes this a specific concern for people who regularly burn candles in enclosed spaces.

Industrial proximity Petroleum refineries, chemical plants, and rubber manufacturing facilities remain significant point sources for community benzene exposure. PollutionProfile's Historical Exposure Recorder links your residential and occupational history to TRI facility data — identifying any periods of proximity to industrial benzene sources in your past.