Analysis of the data on the multi-annual concentrations of B(a)P in 16 Polish provinces (except monitoring data from the stations located within cities with more than 100,000 residents and agglomerations) have shown that the greatest air pollution by B(a)P occurs in the of southern (śląskie, opolskie, and małopolskie provinces) and central regions (łódzkie and mazowieckie provinces) of Poland (Fig. 1). In małopolskie and śląskie provinces, the average concentration of PM10-bound B(a)P in the period 2010–2015 was 9.09 and 7.9 ng/m3, while the provinces lying in the north (like pomorskie and kujawsko-pomorskie) those concentrations were 3.54 and 2.98 ng/m3. In terms of B(a)P concentrations, łódzkie and opolskie provinces overtake the Górnośląska Agglomeration (so-called Upper Silesia), which is the European hot spot area in terms of PM air pollution (Gnauk et al. 2011; Kiesewetter et al. 2015; Petit et al. 2017).
When comparing the mean multi-annual ambient levels of B(a)P within different geographic areas (averaged within 16 provinces: 4.86 ± 2.74 ng/m3, averaged within 12 agglomerations: 4.31 ± 2.82 ng/m3, and averaged within 18 cities: 3.65 ± 1.61 ng/m3), it also turns out that Polish provinces (in fact urban suburbs or villages) are slightly more polluted by PM10-bound B(a)P compared to the biggest cities and agglomerations (Figs. 5, 6, 7). On the other hand, the mean concentrations of B(a)P over 2010–2015 in the remaining areas are not significantly higher (t test, p > 0.05) compared to those measured in agglomerations or cities. This urges the conclusion that the ambient concentration of B(a)P in the Polish area is rather homogenous. According to the estimates by the National Centre for Emission Management (http://www.kobize.pl/), up to 87% of carcinogenic PAHs originate from domestic furnaces and it is associated with the heating of buildings. In fact, burning of solid fuels (coal and wood) in domestic stoves and fireplaces is a major source of carcinogenic PAHs in Poland (Rogula-Kozłowska et al. 2012b; 2013). In small towns and villages, most buildings are heated using individual furnaces: stoves fireplaces and household boilers that do not meet any emission standards and additionally are fueled by of low-quality fuels and (most probably) rubbish (Rogula-Kozłowska et al. 2012a; 2014; 2016). Instead, in big cities, buildings are connected to more eco-friendly heating systems (electrical, natural gas) and coal- or oil-fired heating plants (Majewski and Rogula-Kozłowska 2016). Therefore, even a huge amount of B(a)P emission sources (like cars or factories) most densely concentrated within large cities and agglomerations may not contribute to the excess B(a)P levels to the same extent as small, dispersed municipal sources in urban suburbs or villages. A city with the highest average concentration of B(a)P in the period 2010–2015 was Legnica (6.72 ng/m3) (Fig. 7)—the biggest city in the industrial complex of the Legnica-Głogów Copper District. Similarly, high average concentration of B(a)P over 2010–2015 was found in śląskie cities (for example, in Katowice—6.74 ng/m3, or Zabrze—10.13 ng/m3) and in Kraków (7.20 ng/m3) but also in cities located in the mountain valleys, both in the Carpathians (Zakopane—8.99 ng/m3) and in the Sudeten Mountains (Nowa Ruda—14.73 ng/m3), where the dispersion of pollutants due to topography is rather limited.
According to Fig. 7, none among 18 cities meets the B(a)P target value (annual mean concentration: 1 ng/m3; Directive 2004/107/EC). The best in terms of air pollution by B(a)P are cities located in the zachodniopomorskie, warmińsko-mazurskie, and kujawsko-pomorskie regions, such as Koszalin (mean concentration of PM10-bound B(a)P in the period 2010–2015: 1.6 ng/m3), Olsztyn (1.86 ng/m3), and Toruń (1.78 ng/m3). However, even in those locations, mean concentrations of B(a)P in the period 2010–2015 were almost two times higher than the target value (1 ng/m3).
In fact, in each region of Poland, the concentrations of B(a)P many times exceed those normally meet in other European countries (Rogula-Kozłowska 2015). In Poland, as in the majority of central-eastern European countries, the dependence of economy on coal is still higher than in western European countries. It is because hard coal and lignite amount for approximately 45.5 and 36.7% in the structures of electricity production in Poland (KOBIZE, 2015). In the 80s and 90s, the concentrations of B(a)P in Poland were the highest one recorded in Europe, and perhaps in the world. In some Silesian cities, annual mean concentrations of B(a)P far exceeded 200 ng/m3 (e.g., Ruda Śląska—521 ng/m3, Rogula-Kozłowska et al. 2012b). A comparison against target values and the state of air pollution by B(a)P between Poland and UK indicate that in UK, only 6% of all monitoring stations measured annual mean B(a)P concentration above the EC target value of 1 ng/m3, while in Poland, this number was 96% (CIEP 2016; Tompkins et al. 2016). Despite the existence of the EC standards for ambient B(a)P (Directive 2004/107/EC), in fact, the real threshold concentration of B(a)P below which no adverse health effects will occur cannot be normalized and even very small concentrations of this pollutant can be dangerous for humans (a reference level of 0.12 ng/m3, corresponding to an additional lifetime cancer risk of 1 × 10−5 is the matter of concern) (Guerreiro et al. 2016). In general, results from this study indicate that Polish population exposed to the concentrations of B(a)P typically found in the agglomerations and big cities are at higher risk compared to the exposures found in the remaining areas (urban suburbs or villages) (Figs. 5,6,7). This is in good agreement to the popular opinion that regions characterized by enormous concentration of industry and roads like, for example, cities in the Silesia or Masovian region are more “health detrimental”. In other words, areas of high population density correspond to areas of a potentially high health effects. Similar conclusion was drawn by Zhang et al. (2009) who quantify the inhalation exposure to ambient polycyclic aromatic hydrocarbons and lung cancer risk among Chinese population and found that population of major cities had a higher risk of lung cancer than those residing the rural areas. It must be, however, remembered that in this work, the Polish-wide population exposure to B(a)P was calculated as the population-weighted exposure, i.e., the average exposure per hypothetical inhabitant across specific geographic region. Therefore, the obtained lung cancer risk is directly related to the population density and in general higher in areas of higher density. Taking into account diverse population density and most pessimistic scenario, the risk averaged within cities ranged from 7.3E−04 in Zielona Góra to 8.6E−03 in Legnica (Fig. 7), while within remaining areas from 1E−04 in Warmińsko-Mazurskie to 9.1E−04 in Łódzkie (Fig. 5). After exclusion, the influence of the demographic factor (more strictly: population density) from our calculations was found that the greatest risk will be faced by people settled in the remaining areas because of the highest average concentrations of B(a)P. In fact, in countries like Poland, where domestic stoves and furnaces for fossil fuel and biomass make the greatest contribution to PM and PM-bound PAHs emission, the difference in the ambient concentrations of B(a)P between urban, suburban, and rural areas will be hardly observable or even higher in smaller towns, where old and inefficient boilers or furnaces represent the two largest categories of heating systems used. The lowest risk was found in case of regional background sites (Table 1), in the range of 7.15E−07 to 2.41E−04 (pessimistic scenario). The number of additional cancer occurrence in the background sites was still beneath the values found in provinces, approximately by one order of magnitude. When analyzing the standardized number of lung cancer incidences in Polish provinces among man and woman (Polish National Registry of Cancer data, Table 2) for the period 2010–2014, it was found that man’s group dominate in terms of the total cases. Standardized incidence rates differ not only in terms of individual sex-sensitivity, but also in terms of spatial variability. The rates of lung cancer incidences reach top values in the kujawsko-pomorskie, pomorskie, and warmińsko-mazurskie provinces, while the lowest in the podkarpackie, podlaskie, and mazowieckie provinces. By comparing those numbers with the calculated most pessimistic risk values, we found that the estimated multi-annual (2010–2015) incidence of B(a)P-related lung cancer, resulting from the exposure to the B(a)P concentrations averaged within polish provinces (cities, agglomerations, and remaining areas) was 523 cases per million people, and therefore, the contribution of B(a)P inhalation to the total lung cancer cases including smokers in those areas would be approximately 10.8% (among males) and 31.5% (among females) (Table 2, Fig. 8).
This analyses support claims that B(a)P exposures in Polish provinces account for even ~ 31% of the total lung cancer occurrence. Calculated risk is similar to the B(a)P-related cancer risk modelled for whole European population by Guerreiro et al. (2016). Those researchers found that the exposure to the ambient air levels of B(a)P in Europe leads to an estimated 370 lung cancer incidences per year, for the 60% of the whole European population included in the estimation. While extending the analysis to the whole modelled domain, by including regions with a high relative uncertainty of estimated B(a)P concentration (i.e., above 60%), the estimate of lung cancer incidences increases to about 550.