• bitumen
• bitumen fumes
• carcinogenicity
• emission characteristic
• exposure assessment
• polycyclic aromatic hydrocarbons
• road construction

Asphalt has an important share in the road construction as it is the major material used to build roads. Roads are assets to the society and an integral component in the development of a nation’s infrastructure. The production of asphalt and the different phases it goes through before it becomes a road have a massive impact on the environment. For the asphalt production bitumen binder is used.
Bitumen is a complex mixture of organic compounds, primarily composed of high boiling point and high molecular weight hydrocarbons, whose molecules are combinations of the familiar petroleum structural building units. Its physical behavior can be explained by considering it a colloidal system whose properties are influenced by the interactions of various empirically defined generic compound classes.
Bitumen overall composition depends on the composition of the crude petroleum oil from which it is obtained, as well as the techniques used to refine and process it. Bitumens are used to form produce for many applications, including the use of hot-mix, warm mix, reclaimed asphalt mixing in road construction and maintenance.
At ambient temperatures bitumen is a stable, semi-solid substance and does not present any health risks. In road construction industry during manufacturing, storage, transportation and use bitumen is heated giving off hydrocarbon emissions, to which workers may be exposed. Bitumen emissions are complex and variable mixtures of inorganic particulate and organic compounds that include aliphatics, polycyclic aromatic hydrocarbons (PAHs) and heterocyclic aromatic compounds containing sulfur, nitrogen, and oxygen. In recent years there has been increasing interest in investigating the potential of bitumen emissions to cause health effects in exposed workers. Bitumen remains a focus for health effects research however, primarily due to the presence of small amounts of PAHs in the product and uncertainty about the associated health risks from exposure to emissions from hot bitumen. The bitumen industry is working closely with regulatory and scientific bodies to resolve remaining questions. Further studies are in progress, employing state of the art techniques, as Warm Mix Asphalt (WMA), which should resolve finally the question whether exposure to bitumen emissions presents a cancer risk. In addition to the health effects research discussed has been active in promoting strategies to reduce worker exposure to emissions from hot bitumen work. Warm-mix asphalts are produced and placed at temperatures typically 10-40 °C lower that conventional rolled asphalt. With the decreased production temperature comes the additional benefit of reduced emissions from burning fuels, fumes, and odors generated at the plant and the paving site. Disadvantages of WMA are elevate costs and it is only about 3 to 8 years (depending on method) since the earliest WMA field tests were started and therefore its long-term performance is still unproven.
Workers in road construction industry include asphalt plant workers, ground construction workers and road paving workers. These individuals can be exposed to a wide range of potentially hazardous substances emitted from hot bitumen. Modern road paving workers are typically exposed to 0.1 to 2 mg/m3 of bitumen fume which includes 10 to 200 ng/m3 of benzo(a)pyrene. Information on determinants of other exposures in road construction is either absent or limited.
International Agency for Research on Cancer (IARC) historical cohort study of asphalt industry since 1993, evaluated in 2011 bitumen emissions as possible carcinogenic to humans during road paving. Bitumen fume exposures during asphalt plants or outdoor hot mix paving and surface dressing can be expected to be similar. This comparison can be confounded by presence on organic matter of non-bitumen origin. Exposure to PAH can be anticipated to be elevated, when coal tar is added to paving mixtures. There is also some evidence that the exposures have been higher in the past. However, misclassification of exposure in such grouping can be expected to be substantial and its magnitude and direction would be impossible to quantify. Assembling industrial hygiene measurements from various studies into a single database and obtaining access to unpublished data may help refine exposure assessment in road construction industry.
Very little information is available regarding environmental exposure to asphalt emissions. Results from direct human exposure monitoring indicate that the physical character of asphalt emissions released to the atmosphere during paving operations is composed of mineral particulate matter and hydrocarbons, including higher molecular weight PAHs. Estimates of total atmospheric PAH emissions suggest that the contributions from the paving industry are very small. The PAHs that are released will primarily adsorb to airborne particulate matter. Some of these PAHs will be deposited in a few days, while some may remain in the atmosphere for several weeks. No information is available concerning the deposition of airborne asphalt emissions onto land.
Various methods are used to monitor bitumen-derived vapors, aerosols and fumes from heated bitumen. The more conventional methods are Total Particulate Matter (TPM) or solvent soluble/organic particulate matter (e.g., Benzene-Soluble Matter (BSM)). Recently more often the amount of total organic matter (TOM) in both aerosol and vapor is determined. Different official methods for PAH analysis in bitumen fumes have been propose. Due to the existence of numerous structural isomers of the PAHs, chromatographic separation either by Gas Chromatography (GC) coupled with universal Flame Ionization Detection (FID), Mass Spectrometry (MS) or High-Performance Liquid Chromatography (HPLC) coupled with ultraviolet or Fluorescence Detection (FD) is generally employed for isomer-specific identification and quantification.
At present, no international standard for the assessment of exposure to bitumen fume exists. As a result, reported values of exposures over time, between studies within the same country, and between the various countries vary significantly and must be considered carefully as to the intended use.
In order to personal study of bitumen emissions, a special fume generation system has been developed to identify the polycyclic aromatic hydrocarbons and heterocyclic aromatic compounds, emitted from different types of Reclaimed Asphalt Pavement (RAP) regarding two temperature regimes 300 °C and 500 °C. The ten types of heterocyclic aromatic hydrocarbons and seventeen types of PAHs were identified and analyzed in this experiment.
This study shows that increasing temperature leads to an increase of PAHs and heterocyclic aromatic compound emissions. Regarding the assessment of bitumen emissions as possible indicator of carcinogenic exposure, bitumen fumes generated at high temperatures (for 500 °C in our experiment) are more likely to generate polycyclic aromatic hydrocarbons, carcinogenic PAHs, Heterocyclic Aromatic Hydrocarbons than fumes generated at lower temperatures (for 300 °C in our experiment). However, from our results we can note that low temperature produces low emissions, but with higher percent of carcinogenic PAHs and benzene emissions of total emissions. This result seems quite surprising for us.
The obtained results of Relative Carcinogenic Factor (RCF) show that decreasing of temperature leads to a decrease of RCF.
Several studies have dealt with fumes from bitumen emissions, there was report that chemical composition of bitumen fumes varies and depends on crude petroleum sources, type of asphalt, temperature and mixing during the manufacturing process, unfortunately, we do not know the composition of RAP in this experiment, in that case we cannot give more well interpretation of fumes emitted from bitumen. We can just highlight that the temperature of heated bitumen is the key parameter in order to control the emission, and low temperature reduces the possible carcinogenic effect of heated bitumen.
This study would be helpful to monitor health impacts of workers involved in road construction industry.