1. Introduction
Cancer of respiratory tract (trachea, bronchus, and lung cancer–further stated LBC) is the world’s most common cause of death among all cancer diseases [
1]. In the Czech Republic, lung cancer is the third most common cause of death of all diseases and the most common cause of death of all cancer diseases [
2]. The occurrence of LBC is influenced by many risk factors including outdoor air pollution, indoor air pollution, occupational exposure, genetic predisposition and many of lifestyle risk factors, especially tobacco smoking [
3].
Outdoor and indoor air pollution concentrations differ significantly across different parts of the world and also across the Czech Republic (CR) [
4]. Although the respirable fraction of particulate matter PM 2.5, which are emitted from various natural and anthropogenic sources is most associated with premature mortality of LBC [
5,
6], the polycyclic aromatic hydrocarbons, which are linked to PM 2.5, and other genotoxic substances increased carcinogenic potential of inhaled air pollution, where the significant part is probably caused by the proven human carcinogen benzo[a]pyrene [
7], whose inhalation exposure is associated with LBC and also with upper respiratory tract cancer and esophageal cancer [
8].
The Czech Republic is also one of the European countries with the highest concentrations of indoor radon. Radon is found in all buildings in various quantities and the specific concentration in the house is related to the amount of radon present in the subsoil under the building [
9]. Radon is a proven human carcinogen that irradiates the epithelium of respiratory system through the inhalation exposure and probably is the second most important cause of lung cancer after smoking. The effect of radon on the incidence of lung cancer has been convincingly demonstrated by epidemiological studies. Studies have also shown that the combined effects of radon and smoking increase the harmful effects on health [
9,
10].
Professions at risk of development of LBC include mining workers, quarrying professions, professional asbestos exposure or coking plant workers. In the Czech Republic there is a register of occupational diseases which has been a reliable source of databases of this information since 1991 [
11].
Tobacco smoking is the most significant modifiable risk factor from lifestyle risk factors, the main consequence of smoking is the development of respiratory diseases (especially LBC) and cardiovascular diseases, including other diseases. The incidence of cancer, including LBC, and the premature mortality associated with tobacco smoking are considered a global problem [
12]. There are also other risk factors (like genetic predispositions, infectious diseases, other lifestyle risk factors, socioeconomic influences) that cause development of LBC [
3].
The aim of the study was to quantify lifetime cancer risks of LBC (see International Classification of Diseases ICD10–C33, C34) from selected risk factors related to inhalation exposures and their quantitative comparison.
Another aim of the study was to compare the individual contributions of the risk factors between environmentally differently polluted regions.
The volume activity of radon in apartments in the Czech Republic is shown in
Figure 1. Below
Figure 2 shows the five-year average annual average concentrations of benzo[a]pyrene in the period 2014–2018.
4. Discussion
In this study, two regions were selected based on the objectives of the project Healthy Aging in the Industrial Region. The first region is the Moravian–Silesian Region, an industrial area (IA). There is relatively polluted air and other social structures of the population due to the types of employment, including expected different lifestyles. The second region is a non-industrial area (NA), which is the South Bohemian region, which in this sense was considered an industrially unpolluted area.
Carcinogenic risk assessment was performed in a population that showed a relatively uniform distribution by gender, slightly exceeding the number of women (see
Section 2.1). The onset of LBC disease in the study population can be observed from approximately 45 years of age (see
Figure 3) with the highest values in the age category 70–74 years, which agrees with the reported median age of first diagnosis of 70 years [
3]. The incidence of LBC per 100,000 inhabitants in the industrial area (IA) and the non-industrial area (NA) is significantly higher in men (8190 in IA, 7595 in NA) than in women (2022 in IA, 1747 in NA). No statistically significant differences in the incidences thus expressed between areas IA and NA were found (see
Table 1).
Although the incidence of LBC in IA and NA did not differ significantly, lifetime exposures of selected risk factors were different. Radon exposure was approximately 1.5 time higher in NA (77 Bq/m
3 in IA, 120 Bq/m
3 in NA), while benzo[a]pyrene exposure was approximately eight times higher in IA (3.378 ng/m
3 in IA, 0.406 ng/m
3 in NA) (see
Table 2). There was also a significant difference in occupational exposures in employees who are exposed to fibrogenic dust at their workplaces. In IA, the share of these exposures is dominant, while in NA, these professions are almost non-existent. These exposures lead to pneumoconiosis in some of these workers and to LBC as an occupational disease in some workers (see
Table 5).
The population-weighted average volume activity of radon in the NA moved averaged around 120 Bq/m
3, with the highest values in the districts of Strakonice (204 Bq/m
3), the lowest in the district of Tábor (120 Bq/m
3). In IA, the concentration of radon in the dwellings was significantly lower, around 77 Bq/m
3. Comparing the above exposures with data in the literature, it can be stated that the exposure to radon in the monitored areas is relatively high compared to data from other European (or other) countries. For example, J. D. Appleton records in his publication from 2007 an average radon exposure value of 20 Bq/m
3 in the UK, 46 Bq/m
3 in the US and 108 Bq/m
3 in Sweden [
29]. From these radon exposure data, lifetime carcinogenic risks (LR
1) in the IA area were estimated to be around 1200 × 10
−5 (i.e., 1200 newly expected cancers per 100,000 inhabitants during an individual’s life of 75 years), whereas in the NA the carcinogenic risk was significantly higher, around 1800 × 10
−5 (see
Table 3).
Long-term (lifetime) exposures benzo[a]pyrene, especially in industrial area, can also be considered as one of the highest in Europe (average long-term concentration 3.4 ng/m
3 with a maximum of 8.2 ng/m
3 in Ostrava, see
Table 2), in comparison with other states or regions [
30]. The higher occurrence of radon in NA is due to the different geological subsoil in Bohemia (NA) compared to the Silesian region (IA). On the contrary, long-term concentrations of benzo[a]pyrene are naturally significantly higher in the industrial area of Silesia compared to the relatively environmentally unburdened area (average long-term concentration 0.4 ng/m
3, see
Table 2). After processing these exposure data, it was possible to state that lifelong respiration of benzo[a]pyrene represents significantly higher risks (LR
2) in IA compared to NA with different values using carcinogenic risk units by EPA and WHO IARC (see
Table 3 and
Figure 4). The average value of lifetime risk according to EPA was 0.19 × 10
−5, while according to WHO IARC it was 27.5 × 10
−5, which is more than a two-order difference. The WHO IARC still advocates the design of a carcinogenic risk directive by a major study in the workplace after exposure of workers to coke oven emissions [
28], while the EPA evaluates far more evidence and it may be more plausible to estimate this risk [
8]. The results of the B[a]P exposure estimation are based only on the measured BaP concentrations, and it can be reasonably assumed that the carcinogenic potential of all air pollutants is higher in the real situation, due to the content of other cariogenic PAHs or other substances.
The data obtained of exposures to fibrogenic dust are completely dependent on the character of the studied area and depend on employment in many professions where such exposures occur. In our case, the share of exposures in the industrial area was almost 100%. The construction of risks (LR
3) was based on the state register of occupational diseases and previously performed studies in risk professions (see
Section 2.2), where it was possible to evaluate the lifetime risks of LBC from the data obtained in this way. In IA, this risk was 28.5 × 10
−5 for the population (see
Table 5), which can already be considered a significant risk as it exceeds the generally acceptable risk level of 10
−6 [
31].
It is a widely accepted fact that smoking is one of the most important risk factors for lung cancer [
32]. Despite all efforts, the authors failed to obtain relevant data on smoking in individual areas of the Czech Republic, only reliable data on smoking in the population in the Czech Republic as a whole were obtained. The lifetime carcinogenic risks of respiratory cancer could not be assessed, and smoking was included in the so-called other risk factors, together with genetic predispositions, infectious diseases of the respiratory system, nutrition, physical activity, other lifestyle factors and psycho-socio-economic influences or determinants. health (see
Section 2.2) [
3]. The value of this ““other”” lifetime carcinogenic risk (LR
4) ranged from 2739 per 100,000 inhabitants in the non-industrial area to 3426 per 100,000 inhabitants in the industrial area, which are certainly significant values.
The aim of the work was mainly to show the share and comparison of individual contributions to the total lifetime risk or incidence of LBC. The shares (proportions) of lifetime risks of LBCs (LRP
1, LRP
2, LRP
3 and LRP
4) and the actual incidence of this disease can be seen in
Table 4 and
Table 5 and
Figure 6. The highest (100%) proportion was found for radon (LRP
1) in women in NA. It is evident that this share is probably overestimated because the share of other risk factors cannot be zero. Although smoking was not evaluated in our work for the above reasons, it is known that women in the Czech Republic smoke slightly less than men, but the share of women smokers in the total number of women is about 20.7% [
33], i.e., exposure to tobacco smoke would naturally have to be reflected in the occurrence of LBC. The share of the risk of radon exposure in the occurrence of LBC in men in both areas (in IA 15%, in NA 25%) is, therefore, probably lower than shown in
Figure 6 in this work according to ICRP (see
Section 2.2).
The contribution of the lifetime carcinogenic risk of benzo[a]pyrene to the occurrence of respiratory system (LRP
2) is also questionable due to an inconsistent view of its carcinogenic potential, see above. However, one of the other most important ““findings”” of this work is the fact that the carcinogenicity of polluted open air is most likely to be significantly lower (even taking into account the content of other carcinogenic substances) than in the indoor environment of apartments with radioactive radon. The highest estimated share (proportion) of the lifetime carcinogenic risk of benzo[a]pyrene in the incidence of LBC was 0.6% in IA by using the carcinogenic risk directive two orders of magnitude higher of WHO IARC rather than the directive by EPA (see
Table 4).
The contribution of carcinogenic risks of fibrogenic dust in the work environment (LRP
3) to the total incidence of LBC appears to be consistent, as it has been determined from real data. For IA with high employment in high-risk occupations, it was 0.35% and may, therefore, be significant in other industrial regions (see
Table 5). The contribution of other risk factors (LRP
4) to the incidence of respiratory cancer was found to range from 0% for women in NA (see radon risk overestimation discussed above) to 85% for men in IA (see
Figure 6). Given these values, it is evident that the share of smoking and other lifestyle factors plays one of the primary roles in respiratory cancer and is certainly higher than in the share of air pollution. On the other hand, it should be recalled that the estimation of this share is likely to be burdened by high uncertainty for the reasons set out above.