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We investigate epidemiological studies on the potential carcinogenicity of asphalt. In this article, we are There is "inadequate evidence" that bitumens alone are carcinogenic to humans, according to the International Agency for Research on Cancer (IARC), which made this claim in 1984.
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Nonetheless, they concluded that animal data sufficiently supported the carcinogenicity of some steam- and air-refined bitumen extracts.
In the absence of human data, the IARC considered it reasonable to treat chemicals with sufficient evidence of carcinogenicity in animals as if they posed a risk to humans. Since the IARC report.
epidemiological data for men have accumulated, but they do not meet the requirements for demonstrating a causal link between asphalt exposure and the onset of cancer.
All of the studies mentioned lack exposure or potential confounder information, which is required to determine whether or not such an association exists.
At the very least, an appropriate public health attitude implies that action is taken to protect those working with asphalt by monitoring the workplace, taking whatever precautions are possible to reduce exposures, and informing workers of potential hazards in light of the evidence (or lack thereof) regarding asphalt at this time.
Furthermore, to determine whether asphalt exposure increases the risk of cancer in humans, carefully planned analytical epidemiological studies are required.
The carcinogenic potential of bitumen (asphalt) and asphalt fumes continues to be a source of concern.
This is due to the potential presence of polycyclic aromatic hydrocarbons (PAHs) in asphalt (although the precise chemical composition may vary depending on the crude oil source and the manufacturing process).
and it persists despite the theory that the manufacturing process will likely remove nearly all aromatic hydrocarbons known or suspected to be carcinogens.
Vacuum distillation of crude petroleum oils produces asphalt. Steam can be added to the distillation process depending on the specific crude material and the needs of the end users, and the vacuum residue can then be processed further using air blowing or solvent precipitation.
Asphalt products are classified into four types: emulsified asphalts, cutback asphalts, air-blown asphalts, and asphalt cements.
Asphalts are widely used in a wide range of applications such as road construction and maintenance, roofing, and flooring. The vast majority of the remaining material is used in the production and installation of roofing products.
The manufacturing process, chemical composition, and applications are all described in detail by King et al. and IARC. A number of reviews on the carcinogenic potential of petroleum hydrocarbons have been published, but they only touch on asphalt briefly.
Bingham et al. investigated the potential carcinogenicity of petroleum hydrocarbons in 1980.
Animal studies suggested that petroleum-based asphalts could cause cancer, though this possibility appeared to depend on the origin of the asphalt and how the final mixtures were processed.
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These reviewers stated that the available information on the potential contribution of petroleum-derived bitumens to the development of cancer in humans was difficult to interpret.
The lack of epidemiological data and the fact that "the working histories of most individuals in the paving and roofing industries include previous or combined exposure to coal tar.
which is considered by the US National Institute for Occupational Safety and Health to be a known carcinogen" made studying the effects of asphalts difficult.
Although some bitumens applied to the skin of mice show carcinogenic activity, it is low when compared to coal tar, and the toxicity of bitumens is generally accepted.
according to the World Health Organization task group on environmental health criteria for selected petroleum products in 1982 after reviewing the then-current evidence. "Petroleum-based bitumens do not pose a significant health risk," according to a review of available human data.
However, because bitumen and bitumen vapours contain polynuclear aromatic compounds, the reviewers concluded that, despite a lack of supporting data, bitumen and bitumen vapours may contribute to the overall incidence of skin and respiratory tract cancer.
In 1984, the IARC Working Group on the Evaluation of Carcinogenic Risk of Chemicals to Humans examined the evidence regarding bitumen carcinogenicity.
The working group cautioned that bitumens should not be confused with coal tars, which are byproducts of coal tar distillation, or coal tar pitches, which are byproducts of coal tar distillation, as these coal tar products are occasionally used in applications that require bitumens.
However, they claimed that animal data adequately supported the carcinogenicity of some steam and air refined bitumen extracts. The IARC concluded that there is "inadequate evidence that bitumens alone are carcinogenic to humans."
In the absence of human data, the IARC considered it reasonable to treat chemicals with sufficient evidence of carcinogenicity in animals as if they posed a risk to humans.
Rothman and Emmett (1988) briefly discussed asphalt while investigating the carcinogenic potential of various petroleum-derived products.
They concluded that "although petroleum-derived asphalts have consistently been shown to be markedly less carcinogenic than products derived from coal, their carcinogenic potential remains of some concern."
They also claimed that being exposed to the volatile asphalt compounds formed during heating could be more dangerous than being exposed to the entire compound.
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Because these occupations use more than 80% of all asphalts, they concluded that workers in the highway and roofing industries should be evaluated for an increased risk of cancer based on toxicological evidence.
As previously stated, data for men are limited and do not support a causal link between asphalt exposure and cancer. They may, in fact, obscure rather than clarify the problem.
Two 1976 publications are frequently cited: an increase in lung cancer (not statistically significant) among roofers in a population-based death certificate study by Menck and Henderson6, and increased lung cancer and cancer death rates among roofers studied by Hammond et al. 7 Neither study, however, specifically addressed the issue of asphalt exposure.
The first study did not assess exposure; instead, the occupation listed on the death certificate was substituted for asphalt exposure.
The second study was hampered not only by a lack of quantitative measurements of the studied cohort's exposure to asphalt or its constituents, but also by worker exposure to coal tar products and a lack of data on cigarette smoking.
According to all asphalt reviews, bitumen extracts are carcinogenic to experimental animals.
They also agree that more data is required to determine whether there is a potential risk to those who manufacture and use asphalt products as a result of a lack of human data.
The goal of this paper is to examine the most recent (peer-reviewed) epidemiological publications on asphalt's carcinogenic potential in humans to see if any new evidence has emerged since the IARC review.
Despite the fact that the number of epidemiological publications focusing on humans is still limited, numerous studies with conflicting findings regarding any potential link between asphalt exposure and cancer have been published in recent years.
In 1984, Momsen and Aagard conducted a case-control study with 212 bladder cancer patients and 259 healthy controls.
The University of Aarhus' Department of Oncology and Radiotherapy accepted eight cases. Lifetime occupational histories, socioeconomic status, and some demographic factors were collected from both cases and controls via telephone follow-up.
A minimum of one year of employment was required for categorization within a specific industry, and analyses were performed using the job held the longest.
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They report an increased but not statistically significant relative risk of developing bladder cancer for a variety of occupations, including "kerosine or asphalt work" (odds ratio = 312; 95% confidence interval 088-11 00).
Because there was no exposure data provided, and the main occupation from which exposure was inferred did not only involve asphalt, this study is only mildly suggestive at best.
Between 1959 and 1980, Hansen (1989) identified 679 male mastic asphalt workers, with follow-up data collected until January 1, 1985.
Mastic asphalt is a 12-17% hard bitumen-based mixture of fine sand, stone powder, and finely divided limestone that is used for flooring, roofing, and road surfacing. The Danish Cancer Register was used to find cases of newly diagnosed cancers (incidence).
The expected cancer incidence for Danish men was calculated between 1958 and 1982 using age, time, and site-specific cancer incidence rates. There were statistically significant increases in mouth cancer, esophageal cancer, rectum cancer, and lung cancer.
There was no information on exposure, and many of the workers had only been working with asphalt for six years. Furthermore, uncontrollable confounding factors such as smoking and urbanization were present.
Mastic asphalt workers smoked at a significantly higher rate than the general population, and almost all of them lived in cities, compared to 40% of the comparison group. Furthermore, during WWII, some of the cohort may have been exposed to coal tar pitch.
Hansen hypothesizes that exposure to cracking products in heated bitumen fumes contributed to the discovered increase in cancer incidence, and argues that the link is too strong to be explained by confounding or random variation.
However, the evidence is insufficient to prove that asphalt fumes are a potential carcinogen due to a lack of information on asphalt exposure and potential confounding factors.
They do, however, emphasize the importance of further research that takes into account a person's entire work history, as well as information on their exposure to asphalt fumes and potential confounding variables.
Hansen (1989) presents the findings of a historical cohort study of individuals identified from the November 1970 Danish national census in a separate report.
Ten Danish residents over the age of 14 were asked to self-report their profession, trade, and employment on census day.
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Using national record systems available in Denmark, a total of 1320 asphalt workers and 43 024 other unskilled workers were identified. After that, the cohort was followed for ten years.
Asphalt workers' mortality rates were compared to those of other unskilled workers. SMRs for bladder and respiratory cancers increased, but only marginally.
The author discusses a number of potential errors. The most serious flaw is the categorization of "exposure" as employment on a single day.
According to the author, mortality comparisons between the two groups may not accurately reflect differences in asphalt experience because the exposed category may include people who have had brief, low, or even no exposure, while the unexposed category may include people who have already been exposed.
Furthermore, the exposed and unexposed groups' lifestyles may differ, which may affect how they experience mortality. As a result, this study cannot determine whether there is a link between asphalt exposure and human cancer.
The deaths of highway workers in Minnesota and California have been investigated.
Maizlish et al. conducted a PMR analysis of California Department of Transportation employees who left their jobs for any reason between 1970 and 1983 and died in California between those dates in 1988.
Based on animal studies, there is general agreement that asphalt may pose such a risk, even though epidemiological data to date are insufficient to suggest whether asphalt poses a cancer risk to humans with any degree of scientific certainty.
If asphalt exposure causes cancer in humans, it must be proven through meticulously planned analytical epidemiological studies.
It is pointless to conduct additional descriptive studies with the same flaws as the previous ones. New strategies are required because there hasn't been much progress toward solving the problem in the last 15 years.
Future studies must include information on both exposure and potential confounders. Such studies would require a significant investment of time and money, but the investment would be justified given the large number of workers who could be exposed.
What, if anything, should be done at this point is debatable.
The more conservative assumption is that there is no risk until it is scientifically proven, and the public health attitude, which accepts the risk of being overly concerned about an unknown problem, does not have to be incompatible.
While waiting for "scientific certainty," actions can be taken in the meantime.
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The potential of the "public health attitude" is demonstrated in reports by Silverstein et al. and Knecht and Woitowitz, which identify potential problems and recommend appropriate corrective action before establishing risk with "scientific certainty."
In Germany, tar bitumen is used as a binder in asphalt mixes used in road construction or the laying of load-bearing binding and surface layers, according to the second study.
Tar bitumen is a common product that contains between 25 and 30% special coal tar pitch and roughly 70% road bitumen.
Although it is unknown how common the practice of blending coal tar pitch with asphalt in road paving is worldwide, their research emphasizes the point here.
It concentrated on the PAH profile in tar bitumen road construction and discovered that several cancer-causing PAHs, including benzo(a)pyrene, could be quantified.
Because variables such as fluctuating asphalt mix temperatures and binder pitch content cause significant variation in the PAH content of the daily profile, the PAH content of the daily profile poses an identifiable potential carcinogenic risk.
They contend that, even in the absence of additional research, the continued use of tar bitumen in road construction should be called into question, and that it should be investigated whether another substance could replace coal tar as the binder.
This action would be in line with the previously mentioned "public health attitude." Without a doubt, recent changes to the asphalt roofing manufacturing process have reduced exposure to asphalt fumes.
A dry felt made from waste paper or rags was once immersed in asphalt as part of the roofing felt manufacturing process. When repairing a "break" in the production line, the immersion process may result in significant exposure.
Many roofing felts are now made of fiberglass, which does not require immersion, lowering the risk of exposure on the assembly line.
Chong et al.7 go even further, recommending the implementation of a practical asphalt standard-setting strategy. This essay does not cover the topic of asphalt risk assessment and standardization.
In our opinion, an appropriate public health attitude requires action to protect those working with asphalt by monitoring the workplace, taking all reasonable precautions to reduce exposures, and informing workers of potential hazards.
This is because of the current evidence—or lack thereof—about asphalt. Simultaneous analytical epidemiological studies must be conducted to determine whether asphalt exposure causes cancer in humans.
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