The professional activities involving bitumen are numerous and employ large numbers of workers. Certain warning signs observed in workers incited representatives of the French Federation of Construction Workers - General Work Confederation (FNSC-CGT) to take the initiative and submit a request for ANSES to assess the health risks of bitumen in 2008.
Bitumen: origin, function and use
Bitumen is a residue of petroleum refining and is used mainly in road surfacing work. It is the main, and often exclusive, ingredient in a binder that provides surface adhesion (road pavement, waterproof roofing, etc.). Average French consumption of bitumen is estimated at over 3 million tonnes per year (from 2000 to 2010), with over 90% used for road-based applications (mainly the maintenance of existing roadways), and the remaining 10% used for industrial applications (waterproofing and insulation). In the past, binding was provided through the use of coal tar and other bituminous coal-based products which have gradually been replaced by bitumen. While bitumen and coal tar are usually used interchangeably in English, they are quite distinct substances, both with regard to their basic chemical make-up and their properties.
A complex substance
As a distillation residue, bitumen is a blend of various chemical compounds (over 10,000) whose precise composition is impossible to list. In fact, depending on the origin of the raw petroleum used and on the production process applied, many different types of bitumen with diverse properties may be manufactured. In addition, it may be supplemented with one or several additives, often in very small quantities (less than 1% of the binder), to confer on the bitumen specific properties. Because of this, it is impossible to establish a typical composition profile for bitumen.
Multiple exposure risks
Whether in the road construction and maintenance sector or in the waterproofing of roofs and terraces, the various uses of bituminous binders can cause workers to be directly exposed to bitumen and more importantly to its emissions, when it is heated prior to use. The emissions produced by heating vary greatly depending on the process used, the types of products used and the type of work being performed. They are made up of airborne particles, fumes and gases.
Exposure of workers to bituminous binders and their emissions involves the following routes:
- respiratory, through inhalation of emissions;
- cutaneous, through direct contact with the products, substance residues settling on the skin or possibly through contact from soiled clothing;
- oral, via ingestion of products or their emissions (especially hand-to-mouth contact).
There are currently numerous limitations to the assessment of worker exposure, due in particular to difficulties in taking atmospheric as well as skin measurements. Since there is no harmonisation on either the national or international level, ANSES encourages the systematic implementation of two methods for the characterisation of exposure of workers to bituminous emissions, one with a preventive, global approach to reducing exposure, and the other more specific, employing a medical investigation-type approach. In addition, benzo(a)pyrene, the traditional marker of cancer risk as measured in bituminous binder emissions, is no longer the only relevant marker, and ANSES has issued research recommendations for the monitoring of other compounds in order to improve comprehension of the health risk.
Health effects to take into account
Among the compounds identified in bitumen and its emissions, some have been listed as carcinogenic by the International Agency for Research on Cancer (IARC) and/or listed as carcinogenic, mutagenic, toxic to reproduction (CMR) and/or hazardous by the European Union. The IARC recently identified exposure to oxidised bitumen and its emissions during waterproofing procedures as probably carcinogenic to humans and exposure to bitumen and its emissions during the application of bituminous asphalt concrete and/or during paving work as possibly carcinogenic.
In addition to their carcinogenic potential, epidemiological studies have shown that worker exposure to bituminous products and their emissions are linked to respiratory effects (asthma, chronic bronchitis, etc.). Cardiovascular and immunotoxic effects are also suspected.
It is also important to keep in mind that workers are exposed to other risk factors which may potentially be responsible for health effects (solar radiation, co-exposure with particles, especially diesel engine emissions, contact with hot materials or equipment, noise, repetitive movements, etc.). For cutaneous effects, ANSES emphasises that it is not possible, in the current state of knowledge, to draw clear conclusions concerning the existence or absence of a risk of developing skin cancer in workers exposed to bituminous emissions and that further data are also needed in order to assess the combined effects of co-exposure to bituminous emissions and solar radiation. The initial results of original research work funded by ANSES have not made it possible for any conclusions to be reached at the current time. ANSES encourages development of research initiatives on these issues.
Reducing exposure: a necessity
The studies conducted by ANSES have concluded that a health risk linked to worker exposure to bituminous binders and their emissions does exist. Consequently, professional exposure to bituminous binders and their emissions should be reduced. Reduction of this exposure must first be made through collective prevention measures and efforts based on modifications in work organisation, which would reduce and/or capture the fumes emitted, as well as to reduce the impact of both heat and of co-exposure to bituminous products and solar radiation.
Chemical risk prevention is necessary, in particular through the drafting of a harmonised classification of bitumen with regard to its respiratory effects and in accordance with the terms of the "CLP" European regulation.
Lastly, ANSES also wishes to draw attention to an emerging national issue. In order to cut costs, the majority of all current road work involves the renovation and maintenance of existing networks, which implies performing recycling and planing work on older road surfaces. ANSES therefore insists on the importance of carefully monitoring the potentially dangerous emissions (asbestos, tars, etc.) generated during these operations.
CLP: Classification, Labelling, Packaging; Regulation (EC) no 1272/2008 of the European Parliament and of the Council of 16 December 2008 on classification, labelling and packaging of substances and mixtures, amending and repealing Directives 67/548/EEC and 1999/45/EC and amending Regulation (EC) no 1907/2006.