Assessing cancer hazards of bitumen emissions – a case study for complex petroleum substances

Abstract

When assessing cancer hazard and risk associated with a complex petroleum substance, like bitumen emissions, there are often conflicting results related to human, animal and mechanistic studies. Validation of the complex composition to assure that it matches real-world exposures and control of confounders are pivotal factors in study design to allow the necessary read-across during assessments. Several key studies on bitumen emissions in two-year dermal cancer assays reported variable outcomes ranging from high cancer incidence to no cancer incidence. Here, we synthesize findings from published studies to explain the differences and discuss critical factors in cancer hazard evaluation for complex petroleum substances. Using these critical factors, we reviewed relevant human genetic toxicity, mammalian toxicity and mechanistic studies with bitumen to understand the divergence in results. We assess the most reliable and scientifically supported information on the potential carcinogenic hazards of bitumen emissions and comment on quality and completeness of data. Human hazard data are typically considered highest priority because they eliminate the need for interspecies extrapolation and reduce the range of high -to low-dose extrapolation during the risk assessment process. Finally, two well-conducted comprehensive animal studies are discussed that have well-defined test material, exposure concentration and composition representative of worker exposure, evidence of systemic uptake, no confounding exposures and provide consistency across all elements within both studies. Studies that allow effective read-across from human, animal and mechanistic components, control for confounders and are well-validated analytically against workplace exposures, provide the strongest evidence base for evaluating cancer hazard. ARTICLE HISTORY

Asphalt-related emissions are a major missing nontraditional source of secondary organic aerosol precursors

“…The highly aromatic sulfur-containing compound emissions include formulas representing benzothiophenes and dibenzothiophenes, a selection of which have been previously observed as individual compounds (fig. S6) ( 45 , 46 ). However, previous studies have not reported the wide range of other aromatic and non-aromatic sulfur-containing compounds in asphalt-related emissions.…”

Inherently Functionalized Carbon from Algae to Adsorb Precursors of Secondary Organic Aerosols in Noncombustion Sources

“…The highly aromatic S-containing compounds in bitumen emissions include chemical structures representing benzo-thiophenes and dibenzo-thiophenes . The complex mixture of O-containing emissions includes chemical structures representing benzofurans and dibenzofurans, commonly found in complex petroleum-based mixtures.…”

“…These active organic compounds function as precursors to ozone and SOAs. , Asphalt pavement and asphalt binder (bitumen; a petroleum-derived substance) have been identified as a potential missing source of volatile and semivolatile organic compounds that are released into the atmosphere in the form of gas or aerosol . Bitumen emissions include thousands of individual chemical compounds that eventually form particles with varying aerodynamic diameters (from nm to μm) and different toxicological properties that can be a potential hazard for human health and climate. , These emissions are temperature-dependent compounds that are doubled in a temperature rise from 40 to 60 °C; they reach the maximum level at temperatures over 140 °C, indicating that SOA precursors are released into the air more significantly in summer months . Exposure to ultraviolet is also an influential factor accelerating the emission of volatile and semivolatile organic compounds from areas surfaced with bitumen.…”

Reducing the Carbon Footprint of Bituminous Composites Using Amine-Impregnated Zeolite

“…Many compounds of bitumen are polar compounds carrying S-, N-, and O-containing functional groups such as thiol, amine, amide, phenol, carboxyl, and alcohol. In our list of polar compounds selected for interaction with zeolite, some polar compounds such as benzoic acid, benzofuran, hexanethiol, and hexanal are volatile or semi-volatile compounds of bitumen that can be emitted from the bituminous composites, negatively impacting both air quality and the durability of composites. , For many years, asphalt pavement and asphalt binder (bitumen) have been known as sources of hazardous emissions during hot applications . However, recent findings show that asphalt emissions are not limited to high temperatures during the production of asphalt mixtures or paving operations; there are continuous emissions at ambient temperatures, and the emissions significantly worsen when surfaces are exposed to solar radiation or high temperatures …”

“…68,69 For many years, asphalt pavement and asphalt binder (bitumen) have been known as sources of hazardous emissions during hot applications. 70 However, recent findings show that asphalt emissions are not limited to high temperatures during the production of asphalt mixtures or paving operations; there are continuous emissions at ambient temperatures, and the emissions significantly worsen when surfaces are exposed to solar radiation or high temperatures. 12 ■ RESULTS AND DISCUSSION Laboratory Experiments.…”