Asphalt is a common material used for roads, driveways, and parking lots. Often called blacktop, it’s a durable and flexible composite. Concerns about its potential health effects, particularly cancer risk, are common. This article clarifies the scientific understanding of asphalt and cancer risk.
What Asphalt Is Made Of
Asphalt primarily consists of aggregates and a binder. Aggregates, such as crushed stone, sand, and gravel, form the bulk of the material and provide structural strength. The binder is bitumen, a viscous, black substance derived from crude oil, which acts as a glue holding the particles together.
When heated for mixing, bitumen releases compounds into the air. These emissions contain polycyclic aromatic hydrocarbons (PAHs) and volatile organic compounds (VOCs). PAHs are organic compounds, some of which are hazardous. VOCs are chemicals that readily evaporate at room temperature, including benzene, toluene, and xylene.
Pathways of Exposure
Exposure to asphalt emissions occurs primarily through occupational and general public pathways. Workers in industries like road paving and roofing have direct, prolonged contact with asphalt and its fumes. Occupational settings involve handling hot asphalt, leading to fume inhalation and potential skin contact. Fumes are prevalent during hot mix asphalt application, as high temperatures cause VOCs and PAHs to volatilize.
For the general public, exposure is incidental and of shorter duration. This can occur near active paving operations or from newly laid asphalt. While fume inhalation is possible, intensity and duration are significantly lower than in occupational settings. Skin contact for the general public is less common but can occur with fresh asphalt.
Current Scientific Understanding of Cancer Risk
Major health organizations have investigated whether asphalt causes cancer. The International Agency for Research on Cancer (IARC) classifies occupational exposure to straight-run bitumen and its emissions during road paving as “possibly carcinogenic to humans” (Group 2B). This classification indicates limited evidence of carcinogenicity in humans and less than sufficient evidence in experimental animals, or adequate evidence in animals with limited or inadequate human data. For oxidized bitumen and its emissions, typically used in roofing, the IARC classification is “probably carcinogenic to humans” (Group 2A), suggesting stronger evidence.
Studies have explored the link between asphalt exposure and cancers like lung, skin, and bladder cancer. Some research suggests an increased lung cancer risk among asphalt workers, though confounding factors like smoking or co-exposure to coal tar or diesel exhaust can complicate findings. Evidence points to a higher risk for workers with chronic, high-level exposure. Conversely, the risk for the general public from incidental or short-term exposure is considered very low due to significantly lower exposure levels and durations compared to occupational settings. While some asphalt components, like certain PAHs, are known carcinogens, the overall risk depends heavily on the specific type, duration, and intensity of exposure.
Minimizing Your Exposure
Reducing exposure to asphalt emissions is important, particularly for workers. For workers, engineering controls are a primary strategy, such as using heating systems that maintain constant asphalt temperature and employing emission capture and exhaust systems. Proper ventilation is also important to disperse fumes, and some equipment designs incorporate cooling systems to minimize heat and fumes.
Personal protective equipment (PPE) offers another layer of defense. This includes long-sleeved clothing, gloves, and appropriate footwear to prevent skin contact and burns. Respiratory protection, such as respirators with organic vapor cartridges, can filter out harmful fumes, especially in enclosed spaces or with high fume concentrations. Practicing good personal hygiene, like washing hands before eating and showering after work, helps minimize chemical absorption.
For the general public, minimizing exposure is straightforward. Avoid direct contact with fresh asphalt and stay away from active paving operations. If accidental contact occurs, wash the affected skin area with soap and water. Casual, short-term exposure, like walking or driving on a newly paved road, carries minimal risk due to low intensity and brief duration.