Asphalt Cancer Mortality Rate is way higher among unskilled men
A historical cohort study was used to investigate the possible link between asphalt exposure and the development of cancer to measure the mortality rate.
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In total, 1320 unskilled workers in the asphalt industry were followed up on for ten years and their cause-specific mortality was compared to 43,024 unskilled men.
There was a comparison between the two groups and for unskilled men, it was way higher. Census records were used to identify both groups, and the information from the census records was confirmed using an automatic record link that had previously been established between the census register, the National Register, and the Death Certificate Register.
After allowing for a five-year latency period, there was a statistically significant increase in cancer mortality among asphalt workers aged 45 and up (standardized mortality ratio for cancer: 159; 95% confidence interval: 106-228).
Despite the fact that increases in cases of respiratory, bladder, and digestive cancers were not statistically significant, there was a significant increase in cases of brain cancer (SMR = 500, 95% CI: 103-1461).
Certain components of asphalt fumes may have played a significant role in the observed link between working in the asphalt industry and an increased risk of cancer.
It is possible that workers will be exposed to bitumen fumes while producing asphalt mixes and roofing materials. Depending on the manufacturing process, additional exposure to other substances such as silica dust, organic solvents, acid amines, coal tars, and fungicides is possible.
Inhaling bitumen fumes has been linked to an increased risk of developing cancer, according to one theory. Mice exposed to condensed bitumen fumes on their skin recently revealed that the fumes had a significant carcinogenic effect on the mice.
The yield of malignant neoplasms in mice exposed to bitumen fume condensate was found to be nearly identical to that of the positive control group, which was painted with condensed coal tar fumes.
Previously, epidemiological studies have shown that roofers exposed to bitumen fumes have a significantly increased risk of dying from cancer.
Menck and Henderson estimated lung cancer mortality for several occupational groups in Los Angeles County using registry data.
They discovered that the lung cancer mortality rate for roofers in Los Angeles County was nearly five times that of the general population.
The findings of Menck and Henderson were published in the journal Chest. 2 Hammond and colleagues conducted another study on the mortality rate of roofers. For twelve years, they followed a group of roofers in the United States identified through union files.
3 They discovered an increased mortality rate among long-term roofers due to malignant neoplasms of the buccal cavity and pharynx, digestive organs, the respiratory system, the prostate gland, the bladder, and the skin, as well as leukaemia.
The roofer groups studied, on the other hand, may have been exposed to both coal tar and bitumen fumes23; as a result, no definitive conclusions regarding the possible association between bitumen fumes and the risk of developing cancer could be drawn.
The goal of this study was to look into the mortality pattern in the Danish asphalt industry, specifically the potential correspondence between this pattern and that seen in roofers' mortality studies.
In terms of cause-specific mortality, asphalt workers, who made up the exposed portion of the cohort, were compared to an unexposed group of unskilled workers. The study was designed as a historical cohort study with exposed and unexposed workers.
The members of the study cohort were identified using data files from a nationwide census that took place in Denmark on November 9, 1970.
On this occasion, all Danes over the age of 14 who were living in the country had their self-reported occupation, trade industry, and employment status recorded on the day of the census. These data were used in the process of selecting study participants.
Only unskilled male workers between the ages of 15 and 74 who were employed on the day of the census were considered for participation in this study.
The exposed group was made up of unskilled male workers in the asphalt industry (at asphalt plants, roofing felt plants, or one tar plant).
The unskilled male workers in service trades (38% of the total comparison group), agriculture and forestry (36%), and specific light industries (26% of the cohort) were exposed.
The Danish National Bureau of Statistics has established an automatic record link between the 1970 census register, the National Register, and the Death Certificate Register (Danish National Bureau of Statistics publications No 37 (1979) and No 41 (1985), both in Danish).
This link is available in both of those publications. As a result, any population identified in the 1970 census records has the potential to be automatically followed up on for cause-specific mortality within ten years of November 9, 1970.
For reasons of confidentiality, the National Bureau of Statistics will only provide a claimant with data that has been aggregated and anonymized.
The automatic record link system was used to identify the cohort members who had died and to determine the circumstances surrounding their deaths.
Members of the cohort were tracked down until November 9, 1980, or until they died or left the country before that date, whichever came first.
Deceased individuals, emigrants, and those who could not be followed up on contributed person-years to the total number of person-years at risk until the day of death, the date of emigration, or the last day of notification in the National Registry, respectively. For those study participants who died, the notified underlying cause of death was used.
Asphalt Cancer Mortality
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The expected number of deaths among asphalt workers was calculated using the death rates of the comparison group of unskilled men and the number of person-years at risk accumulated by the asphalt workers.
Furthermore, the mortality rates of asphalt workers were compared to those of the occupationally active population from the 1970 census in terms of total mortality, cancer mortality, and cardiovascular disease mortality.
For statistical purposes, it was assumed that observed numbers greater than 100 would have a normal distribution (Yates' correction was used). A Poisson distribution was assumed when dealing with smaller numbers.
It was assumed that random variation had no effect on the comparison group's death rates.
There were 113 deaths among asphalt workers and 3811 deaths among members of the comparison population over the ten-year period of follow-up. The cancer mortality rate among asphalt workers was slightly higher.
This was due primarily to an increase in the number of deaths caused by malignant neoplasms of the respiratory tract or urinary bladder. Furthermore, the mortality rate from ischaemic heart disease increased slightly.
With the exception of cancer and ischaemic heart disease, there was a significant decrease in the mortality rate caused by all other natural causes of death. When the analysis was limited to the sixth through tenth years of follow-up, the differences in mortality rates were found to be more pronounced than when the data was collected over ten years.
The death rate from cancer among asphalt workers, in particular, was found to have significantly increased over the course of the study's final five years. Aside from an increase in the number of people dying from respiratory or bladder cancer, an alarmingly high number of people were diagnosed with digestive cancer.
According to the study's findings, working in the Danish asphalt industry appears to be associated with an increased risk of cancers affecting the respiratory system, digestive system, and bladder.
However, before drawing any conclusions from the study, it is necessary to consider the various possible errors that could have occurred during the research.
The mortality rates of asphalt workers were compared to those of unskilled men working in occupations where they were not exposed to carcinogens.
In terms of the demands that their jobs place on their physical strength and fitness, social class, and geographic distribution, the occupational groups that will serve as a basis for comparison were chosen to be analogous to the group of people who work in asphalt plants.
With the exception of occupational exposure to asphalt, the two groups were brought as close to each other as was practically possible in all relevant respects.
It was hoped, in particular, that by employing a comparison group of unskilled workers, they would be able to eliminate the so-called healthy worker effect. These employees had been hand-picked.
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With the exception of age and calendar time stratification, no other method of bias control could be practically implemented.
However, it is possible that the lifestyle habits of the asphalt workers differed from those of the unskilled workers used as a comparison group in this study.
Because smoking is linked to an increased risk of respiratory cancer, bladder cancer, and ischaemic heart disease, all of which are common among asphalt workers, any differences in smoking habits would be of particular interest.
This is due to the fact that smoking is linked to an increased risk of lung cancer, bladder cancer, and ischaemic heart disease.
Despite the fact that smoking is extremely common among men in Denmark, smoking habits differences are likely to have only contributed to a minor degree of positive confounding. 4 In relation to the idea presented by Hernberg5, the actual cohort study was rather insensitive.
The cohort was made up entirely of people who were professionally active and thus in good health, and the follow-up period was relatively short.
There were only a few cancer-related deaths among asphalt workers during the first five years of the study's follow-up. However, there were 29 cancer-related deaths among asphalt workers over the next five years.
This is not only due to the fact that the cohort's members are getting older, but it may also be an indication that an efficient health selection was in place among the asphalt workers prior to the study groups' identification.
Workers who develop symptoms of a fatal disease are likely to be separated at an early stage. One of the consequences would be that the first few years of follow-up would yield only a limited amount of data.
Although it would have been preferable to extend the period of follow-up beyond ten years, logistical constraints made this impossible.
Another factor that influences how sensitive the study is determining and classifying different types of exposure. The only requirements for inclusion in either of the two categories were an individual's occupation and the fact that he was working on the day of the census.
For the purposes of this study, "exposure" refers to the possibility of occupational exposure at the time of study enrollment.
When it comes to studying cancer in relation to factors that may be potential risk factors, cumulative exposure is far more important to consider than point-in-time exposure.
The definition of exposure used obscures the distinction between the study populations that were and were not exposed. People who have previously been exposed may be found in both the exposed and unexposed categories.
Those who have previously been exposed may be classified as unexposed. The fact that the two groups were exposed to slightly different amounts of asphalt could explain the observed mortality differences between asphalt workers and the comparison group.
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Keeping this in mind, it is worth noting that between 1975 and 1980, there was a noticeable increase in the number of asphalt workers aged 45 and up who died from cancer.
The pattern of mortality observed among asphalt plant workers was similar to that observed previously among roofers.
23 Roofers and asphalt plant workers are both exposed to asphalt fumes, and researchers have discovered that malignant neoplasms of the respiratory system, digestive organs, and urinary bladder are significantly more likely to kill roofers than asphalt plant workers.
It is reasonable to consider particulate air pollution as a possible "explanation," and it is tempting to speculate that asphalt fumes could be significant, especially since condensed asphalt fume has been found to be highly carcinogenic to rodents.
Because of the increased mortality observed for these cancer sites, it is important to investigate particulate air pollution as a possible "explanation."
Asphalt fume is a dispersed aerosol containing cracking products from heated bitumen as well as light bitumen components. When bitumen is heated to a high temperature, asphalt fume is produced.
When bitumen fumes are inhaled, the mucous membranes of the respiratory tract are exposed to the toxic substances contained in the fumes.
The majority of inhaled particles are transported to the digestive tract via mucociliary clearance mechanisms in the respiratory system.
The toxic substances found in asphalt fumes may then reach the digestive mucosa and become available for absorption. The substances may enter the bloodstream, be metabolized, and then be eliminated from the body through urine.
As a result, from a biological standpoint, prolonged exposure to asphalt fumes may be linked to an increased risk of malignant neoplasms of the respiratory, digestive, or urinary mucosa. Furthermore, this relationship has been shown to be statistically significant.
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