PAHs in asphalt mixes: The complete guide on risks, regulations and diagnosis
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Time to read 9 min
Summary
Introduction What are PAHs and why are they found in asphalt mixes? Definition and toxicity of PAHs The origin of PAHs in asphalt mixes: confusion between bitumen and tar Health and environmental risks: a danger not to be underestimated A major risk to workers' health A significant ecological impact Current regulations: thresholds, obligations, and management channels PAH concentration thresholds that dictate management PAH testing: an essential step before work When is testing mandatory? The PAH testing process Conclusion: Anticipate for better management Frequently Asked Questions (FAQ) Why trust Pouryère for your soil analysis? To learn more
Introduction
Roads, parking lots, and other transportation infrastructure are ubiquitous in our daily lives. Their surfaces, composed of bituminous asphalt, are designed to last. However, beneath this apparent solidity sometimes lies an invisible danger: Polycyclic Aromatic Hydrocarbons, or PAHs. These chemical compounds, a legacy of past construction practices, now pose major challenges in terms of public health, the environment, and waste management.
Whether you're a project owner, construction company, road manager, or simply a citizen, understanding the issue of PAHs in asphalt has become essential. This comprehensive article guides you through the risks, complex regulations, and diagnostic solutions for the safe and compliant management of our infrastructure.
What are PAHs and why are they found in asphalt?
To grasp the scope of the subject, it is essential to understand the nature of PAHs and their historical link with road surfaces.
Definition and toxicity of PAHs
Polycyclic aromatic hydrocarbons (PAHs) are a family of chemical compounds made up of carbon and hydrogen atoms. They arenatural constituents of coal and petroleum . While some are relatively harmless, a list of 16 PAHs is particularly monitored due to their proven toxicity.
The main danger of PAHs lies in their classification as CMR agents (Carcinogenic, Mutagenic, and Reprotoxic). As highlighted in an article in La Gazette des Communes , these molecules are known for their potential to cause cancer, genetic mutations, and reproductive harm. Exposure, even at low doses but repeatedly, constitutes a serious health risk.
The origin of PAHs in asphalt: confusion between bitumen and tar
The presence of high levels of PAHs in asphalt mixes is not systematic. It is primarily linked to the past use of coal tar as a binder. For decades, tar was used for its adhesive properties. However, tar is a byproduct of coal pyrolysis and contains very high concentrations of PAHs, on the order of several grams per kilogram for certain compounds such as Benzo[a]Pyrene (BaP), classified as a known carcinogen.
Bitumen , on the other hand, is a petroleum derivative. Although it can contain traces of PAHs, its concentrations are infinitely lower than those of tar. Since the 1990s, the use of tar has been progressively phased out in favor of bitumen. However, many older roads, often covered by successive layers of newer asphalt, still contain these tarry materials. Fluxing additives or coal derivatives may also have been used until the mid-2000s, contributing to contamination.
Therefore, it is during work on old infrastructure (construction prior to 1995) that the risk of encountering asphalt loaded with PAHs is highest.
Health and environmental risks: a danger not to be underestimated
The presence of PAHs in asphalt mixes is not a trivial problem. The consequences of exposure or poor management are serious, both for human health and for the ecosystem.
A major risk to workers' health
The first to be exposed are the construction workers. The danger materializes when the asphalt is handled, and especially when heated. Exposure can occur through two main routes:
- By inhalation: Heating, milling, or cutting asphalt releases fumes. These fumes contain PAHs (polycyclic aromatic hydrocarbons) that can be inhaled. The INRS (National Institute for Research and Safety) specifies that the International Agency for Research on Cancer (IARC) has classified exposure to bitumen fumes during road surfacing work as "possibly carcinogenic to humans" (Group 2B) .
- Through skin contact: Smoke particles and condensate can settle on skin, clothing, or tools. Direct contact with contaminated materials is another route of exposure, which can increase the risk of skin cancer.
The health effects range from respiratory and skin irritation and headaches to the long-term development of lung or bladder cancer. One study even highlighted that exposure to asbestos and PAHs was responsible for more than 3,000 new cancer cases per year .
A significant ecological impact
Beyond the health risks, PAHs pose a significant environmental problem. Their presence makes recycling asphalt much more complex . Asphalt with low or no contamination is a valuable resource, 100% recyclable in new formulations. Conversely, asphalt with high PAH levels becomes waste whose management is strictly regulated.
If not managed properly, this waste can contaminate soil and groundwater, spreading pollution far beyond the initial construction site. The challenge is therefore twofold: protecting health and preserving natural resources by promoting a virtuous circular economy.
Current regulations: thresholds, obligations and management channels
Faced with these challenges, French and European authorities have established a strict regulatory framework. European Directive 2008/98/EC on waste and the French Labor Code require project owners to assess risks before any intervention.
The management of asphalt containing PAHs is entirely dictated by their concentration. Precise thresholds determine whether the material can be recycled or must be disposed of through a specific channel.
The concentration thresholds for PAHs that dictate management
The regulations, notably explained in a guide from Cerema, define several critical thresholds, expressed in milligrams per kilogram of dry matter (mg/kg DM), equivalent to parts per million (ppm).
- [PAHs] ≤ 50 mg/kg: The material is considered inert waste. It can be recovered through hot recycling (integrated into the production of new asphalt mixes at a plant) or cold recycling. It can also be disposed of at an Inert Waste Landfill (ISDI). This is the most environmentally sound option.
- 50 mg/kg < [PAHs] ≤ 500 mg/kg: Hot recycling is prohibited as it would cause the PAHs to volatilize. Only cold recycling is permitted. For disposal, the material must be sent to a Non-Hazardous Waste Storage Facility (ISDND).
- [PAHs] > 500 mg/kg: All recycling is prohibited. The material is considered hazardous waste. It must be disposed of in a non-hazardous waste landfill or, for the highest concentrations (often exceeding 1000 mg/kg), in a Hazardous Waste Storage Facility (ISDD), a specific and costly process.
These thresholds are fundamental because they determine not only the protection of workers and the environment, but also the overall economics of a road project.
PAH diagnosis: an essential step before work
Since the management of asphalt depends on its PAH content, it is essential to know this before undertaking any work. This is the role of PAH testing.
When is diagnosis mandatory?
The detection of PAHs, often combined with that of asbestos, is mandatory before any operation likely to impact the integrity of the asphalt:
- Maintenance, rehabilitation or renovation work.
- Creating trenches for laying utility networks.
- Road planing, milling or demolition.
- Installation of street furniture or signage.
This obligation applies to both the public domain (roads, highways, managed by the State, local authorities or concessionary companies) and the private domain (supermarket car parks, condominium roads, etc.).
The process of a PAH diagnosis
The diagnosis is a technical task that must be carried out by trained and equipped professionals. It takes place in several key stages:
1. Documentary study and sampling strategy: The survey operator analyzes the history of the site and defines a sampling strategy to obtain representative samples of the work area.
2. Core sampling: The technician takes core samples from the asphalt. This operation is carried out with the application of water or a dust-collecting gel to prevent the dispersion of asbestos fibers and contaminated particles. Each layer of the core can be analyzed separately.
3. Packaging and sending to the laboratory: The samples are hermetically sealed and sent to a COFRAC accredited analysis laboratory.
4. Laboratory analysis: The reference method for quantifying the 16 priority PAHs is gas chromatography, in accordance with standard NF EN 15527 .
5. Diagnostic Report: The laboratory provides quantitative results, which are compiled into a site survey report. This essential document allows the project owner to define the work procedures and plan the management of future waste.
It should be noted that a rapid qualitative test, the "Pak-Marker", can provide an initial indication on site. However, only a quantitative analysis in a laboratory has regulatory value.
Conclusion: Anticipate to manage better
The issue of PAHs in asphalt mixes is a legacy of the past that demands constant vigilance. Far from being a mere administrative burden, pre-construction testing is a fundamental preventative measure. It protects workers' health, safeguards the environment from diffuse pollution, and optimizes waste management costs by promoting the recovery of non-hazardous materials.
For project owners, anticipating PAH testing ensures their project's regulatory compliance, controls their budget by avoiding additional costs associated with the late discovery of pollution, and demonstrates their social and environmental responsibility. In a construction sector undergoing a major ecological transition, the rigorous management of pollutants like PAHs is more than just an obligation: it's a prerequisite for sustainable construction.
The author of the article: Joseph OLIVIER
Joseph Olivier is an entrepreneur in the environmental sector. Originally from Nantes, he trained in waste management before creating a circular economy consulting firm . In 2022, he co-founded Pouryère with the ambition of addressing citizens' concerns about soil quality in France and access to environmental data.
Frequently Asked Questions (FAQ)
What is bituminous asphalt?
Asphalt, or asphalt, is the surfacing material used for the surface layer of roads, parking lots, and other traffic lanes. It is composed of a mixture of aggregates (sand, gravel) and a hydrocarbon binder, which today is almost exclusively bitumen.
Do all asphalt mixes contain dangerous PAHs?
No. Only older asphalt mixes, made with coal tar or certain additives, have high and dangerous concentrations of PAHs. Modern asphalt mixes, made with pure bitumen, have very low PAH levels and are generally not considered dangerous based on this criterion. The risk is therefore highest on infrastructure built before 1995.
Who is responsible for carrying out the PAH diagnosis?
The responsibility lies with the client or the project owner of the site. This may be a local authority (town hall, department), a motorway company, a property developer, a condominium association or a private owner who commissions work on an asphalt surface.
Can asphalt containing PAHs be recycled?
It depends on the concentration. If the PAH content is less than 50 mg/kg, the asphalt can be recycled using either a hot or cold process. Between 50 and 500 mg/kg, only cold recycling is permitted. Above 500 mg/kg, all recycling is prohibited, and the material must be disposed of as hazardous waste.
What is the cost of a PAH analysis in asphalt mixes?
The cost varies depending on the number of samples, the laboratory, and the urgency of the analysis. The cost of on-site intervention for core sampling must also be included. Often, PAH testing is combined with asbestos surveys. As a guide, a package of simultaneous asbestos/PAH testing, including several core samples, can cost between €1,150 and €2,400 excluding VAT.
Is the PAH diagnosis the same as the asbestos diagnosis?
No, these are two separate assessments that look for different pollutants. However, since asbestos and PAHs can be present in the same old asphalt mixes, it is very common and recommended to carry out both assessments simultaneously. Core sampling can be used for both analyses, which optimizes costs and intervention time.
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