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.

Keywords:

• Asphalt
• fumes
• human
• mammalian
• dermal
• inhalation
• mechanistic
• mutagenicity
• risk assessment
• genetic toxicity
• read-across

Acknowledgements

The authors gratefully acknowledge the comments of six reviewers selected by the Editor who were anonymous to the authors. The comments helped improve the clarity of the paper. We thank Jacqueline Bartek for her assistance in literature searching, procurement, and distribution.

Declaration of interest

The employment affiliation of the authors is as shown on the cover page. This paper was prepared with some financial support from the Asphalt Institute (AI), Lexington Kentucky. AI is an international trade association promoting the quality use of asphalt through their members, training and research (http://www.asphaltinstitute.org/). Heritage Research Group authors received no funding for their contributions. The two consulting authors were compensated by AI for their time devoted to this publication. Although an early draft was reviewed by AI’s HSE committee members, the authors have the sole responsibility for the writing and contents of this paper.

Anthony J. Kriech is VP and Director of Research at Heritage Research Group (HRG) in Indianapolis, IN and a long-time member of the HSE committee for AI. He has published numerous studies on bitumen emissions many of them sponsored by the Asphalt Institute and has presented on numerous occasions around the world on this topic. These included a series of studies sponsored by the National Asphalt Pavement Association (NAPA). HRG, a private, for profit business, is part of The Heritage Group which includes Asphalt Materials, Inc and a diverse set of national and international companies involved in highway construction and materials, environmental services, petroleum refining and chemical manufacturing. Tony has represented the Asphalt industry in many capacities, including as an expert witness for Prop 65 in 2017, and as an industry observer in October 2011 at the IARC Working Group meeting for Monograph 103 evaluating the carcinogenic risks of bitumen and bitumen emissions.

Ceinwen A. Schreiner, Ph.D., ATS is retired from C&C, Consulting in Toxicology, Inc., a consulting group with expertise in petroleum and petrochemical toxicology and environmental safety working with businesses, trade organizations and regulatory agencies to address health effects from exposure to a range of petroleum and products for 17 years. She retired from Mobil Corporation in 2000 with 20 years of service. Dr. Schreiner co-authored the Closure Assessment Document on Asphalts (2010) for the EPA High Production Volume testing program and the subsequent publications. Dr. Schreiner provided a review of reproductive and mechanistic studies for the Asphalt Institute in preparation for their observer role at the IARC Working group meetings on October 2011 (monograph 103) evaluating carcinogenic potential of bitumen and bitumen emissions.

Linda V. Osborn has been a researcher with HRG for 22 years and an analytical chemist with Heritage Environmental Services for 11 years prior. Currently Senior Project Chemist, Linda has designed, implemented, and published numerous bitumen emissions related studies often working in conjunction with government and academia. These included studies sponsored by AI and NAPA. Specialties include analytical chemistry and industrial hygiene related to bitumen emissions. Linda was a contributor to a joint publication between AI and Eurobitume, The Bitumen Industry – A global Perspective: Production, chemistry, use, specification and occupational exposure 3rd edition.

Anthony J. Riley is a retired Senior Toxicologist, having worked in the oil and petrochemical industry for 37 years. A substantial period was spent working for BP, the UK based Oil Company, including work on evaluating health hazards and risks associated with the production and use of bitumen. This included representing the European industry in meetings with regulatory authorities and other scientific bodies, including as an Observer at the IARC Working Group meeting in October 2011 (Monograph 103) evaluating the carcinogenic risks of bitumen and bitumen emissions.

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