Asphalt fumes: The current situation and a peek at the future

The controversy about possible cancer-causing effects of asphalt fumes has been with the roofing industry for quite some time. Since the 1980s, NRCA and other roofing industry groups have been involved with a variety of regulatory and scientific settings where these health concerns have been raised. Making sure the health evidence is fairly evaluated—and asphalt isn't improperly "tarred" with a cancer label—certainly hasn't been easy or cheap.

The bad news is new challenges lie ahead, and the stakes for the roofing industry—in the event of an adverse cancer classification of asphalt fumes—never have been higher. The good news is the roofing industry has anticipated these new challenges, and the initiatives currently under way to address them likely will settle the critical health issues and could bring the industry close to the ultimate vindication of this important roofing material.

Reasons for interest

There are two principal reasons asphalt has been the subject of serious regulatory scrutiny for many years.

First, because of its valuable physical properties, asphalt widely is used in commerce. According to U.S. and European government figures, more than 500,000 paving and roofing industry workers are exposed to asphalt fumes in the United States and Western Europe each year. Therefore, if asphalt fume exposure represents a serious health hazard, the scope of the problem is potentially quite large.

Second, asphalt is made from crude oil, and crude oil and asphalt have trace amounts of chemicals called polynuclear aromatic compounds (PACs), a few of which have produced tumors when painted in high concentrations on the shaved backs of laboratory animals. No convincing evidence has been developed indicating such potentially carcinogenic compounds routinely are present at significant levels in fumes created when asphalt is heated in roofing work, much less that exposure levels pose a significant risk of cancer to roofing workers. However, during the years, researchers have published a number of scientific studies that, though far from conclusive, can be interpreted to suggest a cancer hazard might be related to asphalt fume exposure.

The mere possibility of a cancer risk often is sufficient to draw intense interest in the public health and legal communities if the material in question is widely used in commerce. The controversy about asphalt fumes has proved especially difficult to resolve because the natural desires of regulators, health professionals, attorneys and the industry to protect workers and the public from significant hazards has been frustrated by a lack of persuasive scientific data. And care certainly is necessary because, similar to underregulation, overregulation can have serious consequences.

The track record

Because it is so difficult to prove something does not cause cancer and the roofing industry wants to ensure worker health and safety, it often is difficult to adopt an offensive strategy with regard to health issues such as asphalt fumes. But so far, NRCA and other roofing industry organizations have used a proactive approach to the asphalt fumes issue with success.

Since 1990, a number of government agencies and influential scientific groups have reviewed the available scientific evidence to decide whether to regulate or classify asphalt fumes as a cancer-causing substance. The list includes the California Environmental Protection Agency and federal Occupational Safety and Health Administration (OSHA) during the early 1990s; National Institute of Occupational Safety and Health (NIOSH) and American Conference of Governmental Industrial Hygienists during the mid- and late-1990s; and Cal/OSHA and the World Health Organization's (WHO's) International Programme on Chemical Safety during the early 2000s. In each case, no adequate evidence justifying the classification of asphalt fumes as a cancer-causing substance was found.

These results have been achieved in large measure because of the efforts of a partnership among NRCA; asphalt producers; roofing asphalt product manufacturers; and the United Union of Roofers, Waterproofers and Allied Workers. NRCA and its partners have insisted regulatory decisions be based on sound scientific evidence. In addition, they developed such evidence and identified reasonable ways to control exposures while preserving the ability to install quality roof systems.

New challenges

Although the roofing industry has managed to fend off significant regulatory threats, new challenges loom. Two upcoming proceedings, in particular, could have important ramifications for the roofing industry.

First, in May 2004, the National Toxicology Program (NTP) took the first step in a lengthy process to consider whether to classify asphalt fumes as carcinogenic. NTP, which is part of the U.S. Department of Health and Human Services, is an interagency program consisting of elements of the National Institute of Environmental Health Sciences, NIOSH, and Food and Drug Administration's National Center for Toxicological Research. NTP's mandate includes the publication of a biennial report, "Report on Carcinogens," which contains a list of all substances that either are "known" or "may reasonably be anticipated to be" carcinogens and to which a significant number of people residing in the United States are exposed.

According to current NTP listing criteria, a substance is "known" to be a human carcinogen if there is sufficient evidence of carcinogenicity from human studies that indicates a causal relationship between exposure to the substance and cancer. Research includes epidemiology studies and laboratory studies of human tissues or cells.

A substance is "reasonably anticipated to be" a human carcinogen if there is limited evidence of carcinogenicity in humans or sufficient evidence of carcinogenicity in laboratory animals. Sufficient evidence in animals is demonstrated by positive carcinogenicity findings in two or more species; two or more tissue sites; two or more routes of exposure; or to an unusual degree in a single study with regard to incidence, site, type of tumor or age at onset.

Second, the International Agency for Research on Cancer (IARC) has announced it intends to re-evaluate its existing Monograph for Bitumen (the European term for asphalt), which was published in 1985. IARC was created in 1965 as an extension of WHO, the United Nations' global health arm. IARC's mission includes conducting research regarding the causes of cancer, mechanisms of carcinogenesis and development of scientific strategies for cancer control. IARC's Monograph Program, which began in 1972, publishes in separate volumes (two or three volumes are issued every year) scientific judgments about the evidence for or against carcinogenicity. Each volume addresses a selected chemical, group of chemicals, industrial process, occupational exposure, lifestyle factor or biological agent. IARC Monographs widely are recognized as authoritative regarding the carcinogenicity of a range of human exposures and can have significant regulatory effects in the United States and around the world.

Under the IARC process, substances are classified into one of five groups according to the strength of the published scientific evidence for carcinogenicity: Group 1—carcinogenic to humans; Group 2A—probably carcinogenic to humans; Group 2B—possibly carcinogenic to humans; Group 3—not classifiable as to carcinogenicity to humans; and Group 4—probably not carcinogenic to humans.

IARC's Group 1 is defined similarly to NTP's "known" carcinogen category. And IARC's Groups 2A and 2B correspond roughly to NTP's "may reasonably be anticipated" grouping. Either of these NTP classifications, as well as an IARC rating above 3, can have significant regulatory consequences in the United States.

In the short term, NTP classifications and IARC ratings automatically can trigger provisions of the OSHA Hazard Communication Standard requiring material safety data sheet warnings and product labeling. They also would lead quickly to the listing of asphalt fumes under California's Proposition 65 law. But contractors who have decided to join in the industrywide settlements negotiated by NRCA already are in compliance with Proposition 65 even if asphalt fumes are subsequently listed. (For more information about Proposition 65, refer to "Prop 65 and asphalt roofing work," August 2003 issue, page 28, and "A window of opportunity," May issue, page 38.)

During the longer term, adverse carcinogenicity classifications by NTP or IARC would increase the likelihood of regulatory action, most likely in the occupational safety and health arena. One possible outcome would be a stringent OSHA cancer-based permissible exposure limit (PEL), similar to the draft proposal for a 0.2 mg/m³ PEL OSHA evaluated but did not implement during the early 1990s. The draft proposal would have represented a 25-fold reduction from the 5 mg/m³ PEL reaffirmed earlier this year by Cal/OSHA. OSHA was persuaded by intensive scientific and regulatory advocacy by the asphalt industry and others; however, the task would be much greater now in the wake of adverse classifications by NTP, IARC or both.

An OSHA standard likely would require routine exposure monitoring and medical surveillance, restricted-access areas, warning signs, additional container labeling, training, protective clothing and equipment, and hygiene requirements. Depending on the assessment of the contribution of dermal exposures to overall risk (one of the important scientific issues under active consideration by asphalt researchers and others), an OSHA standard also might include additional potentially onerous requirements such as mandatory showers, changing rooms, laundering of work clothing, additional medical testing to monitor workers for dermal exposures, etc.

The longer-term consequences might not be limited to regulatory actions, of course. Particularly because lung cancer is the issue, more lawsuits can be expected, especially if stringent cancer-based regulations are enacted. And liability insurance costs surely would increase accordingly. Regulatory costs and legal exposures might mean reduced market share, bankruptcies or worker layoffs for contractors specializing in built-up and modified bitumen roofing. And if respirators are needed to meet a stringent new PEL, the result might be the creation of new health and safety hazards.

Some hope?

So even after more than 15 years of sustained effort, the asphalt roofing industry still has more work to do if it is to ensure asphalt remains fully available in the marketplace without the tarnish of a cancer label and all that comes with it. What is different now is that in light of the significant strides made in the scientific understanding of an extraordinarily complicated set of issues, the stage has been set for new studies that might go a long way toward settling the cancer question. And NRCA and its partners are expected to be as active as possible in finding the scientific answers.

Aside from the presence of trace levels of PACs in asphalt, the concerns about possible carcinogenicity arise from studies in humans and animals. A number of ongoing research programs provide reason for hope of significant progress in both types of evidence.

With regard to studies in humans, IARC is conducting a study of lung cancer among paving, roofing and other kinds of asphalt workers in seven European countries. The earlier phase of this study found, among other things, a small increase in lung cancer risk among the workers in the study. However, investigators were not able to determine to what extent the cancer risk was attributable to asphalt or several other possible factors (called "confounders" by scientists), including coal-tar exposure and tobacco smoking. IARC's follow-up study specifically is designed to examine the role of these and other possible explanations by specifically investigating the prevalence and intensity of the exposures of the workers in the study to these agents. NRCA is a sponsor of the study and, with its U.S. roofing industry partners, has joined several European asphalt organizations to provide assistance to IARC investigators, particularly with regard to documenting exposures to confounders among roofing workers included in the study.

Similarly, a series of earlier human studies have found increased lung cancer risks among roofing workers, and these studies often are cited as a primary basis for classifying asphalt fumes as carcinogenic. As in the case of the IARC study, these studies are inconclusive because they did not gather the information needed to rule out the potential contribution of confounders in the outcomes. Unlike the IARC study, these earlier studies are completed and the specific role of confounders in the outcomes cannot be examined directly. Nevertheless, scientists have developed statistical methods for reconstructing the potential role of "confounders" in completed studies. NRCA and its partners are sponsoring a study that will use such methods to investigate whether confounding exposures to other agents (coal tar, tobacco smoke, etc.) may be responsible for the excess lung cancer risks seen in these studies.

Regarding animal studies, the concerns about asphalt fumes arise primarily from two NIOSH studies conducted in the 1980s in which laboratory-generated fumes caused skin tumors in mice after dermal application.

Extensive industry research during the 1990s revealed the results of the NIOSH "skin-painting" studies may not be representative of risks in real-world operations because the NIOSH laboratory procedure generated "fumes" that were markedly different from those created in the field.

More recently, researchers from industry and independent groups have developed a fume-generation protocol that has been validated as representative of asphalt paving operations. This protocol is being used in an animal inhalation study of paving fumes in Germany, which is expected to be completed in 2005. This study not only will use a representative sample of real-world fumes, but it involves exposure by inhalation, which is believed to be the primary route of human exposure to asphalt fumes.

NRCA and industry groups are sponsoring a study that will adapt this protocol to generate fumes representative of hot asphalt operations in the field. Once that program is complete, it will be possible to conduct a variety of different studies to better evaluate the potential hazard than the 1980s NIOSH studies were able to accomplish.

The U.S. asphalt industry has urged NTP and IARC to defer their planned evaluations of the carcinogenicity of asphalt fumes until after the ongoing programs have been completed.

But whether NTP and IARC see the wisdom in that proposed course of action, it is clear the ultimate answers to the longstanding questions about the possible carcinogenicity of asphalt fumes may well lie in the ongoing research initiatives. And if that happens, the proactive approach NRCA and its partners have taken from the beginning will produce a good, fact-based result for the roofing industry, its workers, building owners and the public.

Art Sampson is special counsel to NRCA for environmental, health and safety regulatory matters. Sampson is licensed to practice law in Washington, D.C., and maintains his office in Fairfax, Va.