1. Introduction
Polycyclic aromatic hydrocarbons (PAHs) are organic compounds containing only hydrogen and carbon that are composed of two or more fused aromatic rings [
1]. They are abundant in soils and marine sediments, fresh water, and in the atmosphere, where they are predominantly bound to fine particles [
2]. PAHs are persistent compounds, having a wide range of toxicity with all environmental elements. In 1983, the United States Environmental Protection Agency (USEPA) declared 16 PAHs as priority pollutants due to their high concentration, long persistence and toxicity [
3]. Several PAHs exhibit carcinogenic activity: benzo[a]pyrene is carcinogenic to humans (Group 1); cyclopenta[c,d]pyrene, dibenz[a,h]anthracene and dibenzo[a,l]pyrene are probably carcinogenic (Group 2A); and naphthalene, benz[j]aceanthrylene, benz[a]anthracene, benzo[b]fluoranthene, benzo[j]fluoranthene, benzo[k]fluoranthene, benzo[c]phenanthrene, chrysene, dibenzo[a,h]pyrene, dibenzo[a,i]-pyrene, indeno[1,2,3-cd]pyrene and 5-methylchrysene are possibly carcinogenic (Group 2B) [
4]. The carcinogenicity of PAHs in humans has been evidenced in cases of colon, skin, lung, bladder and kidney cancer [
5]. Studies have shown that the risk of developing multiple myeloma and prostate, colon, rectum, bladder, skin, lung and testicular cancer is higher in firefighters than in other professional groups [
6,
7,
8,
9,
10,
11]. PAHs are also considered to be mutagenic, teratogenic, genotoxic and endocrine-disrupting chemicals, and they have important cardiovascular implications [
4,
12,
13,
14].
The sources of PAH pollution are anthropogenic and natural emissions [
15,
16,
17], mainly combined with incomplete combustion [
17,
18,
19,
20,
21]. The phenomenon of incomplete combustion occurs during all fires and can release significant quantities of harmful substances such as trace gases and particulate matter into the atmosphere [
20,
22,
23]. Large fires, both those resulting from industrial accidents and natural fires, especially wildfires, often deteriorate air quality in large areas leading to noticeable health and environmental effects [
24,
25,
26,
27]. Depending on the type of materials burned (e.g., wood, grass, cars, buildings with all equipment incl. flooring, upholstery, paints and coatings, bedding, draperies, etc.), and the conditions and phase of the fire, the type and amount of the produced substances may differ significantly [
7]. Additionally, the smoke produced during a fire is a mixture of many compounds, and its toxicity is very diverse because each combustion condition and type of material burnt generate a unique composition [
7,
20,
24].
Toxic and carcinogenic substances such as heavy metals or organic compounds, including both gaseous-phase and PM-bound PAHs, are released during combustion [
24]; thus, firefighters are at risk of inhaling them during fire suppression. These compounds also deposit on firefighters’ clothing and personal protective equipment (PPE) and are then released into the air in fire vehicles, and later, in fire brigade buildings. Firefighters inhale these hazardous compounds long after the end of firefighting activities while on duty at the fire station [
6,
12,
13,
22,
28,
29,
30,
31,
32]. Moreover, in fire stations, diesel exhaust fumes may occur [
33,
34], especially when garages do not have appropriate ventilation systems and contaminants are deposited on equipment used during rescue operations, e.g., rescue spreaders, saws, and cutters. Thus, firefighting is considered a very high-risk profession and carcinogenic PAHs are an occupational health hazard for firefighters [
4,
31,
35,
36,
37,
38,
39,
40,
41].
Unfortunately, firefighters’ risk of exposure to PAHs is likely to increase, as new compounds such as modern synthetic materials produce PAHs when burned. Moreover, firefighters are not only exposed to PAHs through inhalation, but also through dermal contact with PAHs from a build-up of soot and debris [
42]. However, there is little research on the types and sources of PAHs in fire stations and it is insufficient for a comprehensive risk assessment.
The PAH pollution level has become a significant issue due to health concerns, particularly in fire stations, where the risk of human exposure to atmospheric PAHs appears to be higher. PAHs in the particulate phase pose the greatest threat to health in fire brigades’ garages [
41]. Studies indicated that PAHs with the highest toxicity equivalent factor (TEF), containing 5–6 rings, are mainly in the solid phase [
15,
43,
44,
45]. Therefore, this study aimed to: (1) measure concentrations of different PM fractions in a fire station unit garage, (2) characterize PAH air pollution in PM4 and TSP and (3) evaluate the associated firefighters’ carcinogenic risks. Identification of possible emission sources of PAHs using statistical analyses is an additional goal of the research.
2. Materials and Methods
2.1. Sampling Site
The fire station is located in southwest Poland (51.520044; 17.286005) beyond the central zones of a small town with a population of 11,500 and was considered an urban–rural community. The atmospheric air quality in the studied municipality is better than the average in Poland and is mainly shaped by emissions from households and individual conventional heating sources. Outdoor air quality around the nearest firehouse is influenced by traffic emissions from the national road passing through the town. The expressway is about 25 km away.
The firefighting and rescue unit (FRU) is located in a building with two aboveground stories. On the first floor, there are FRU garages, a hall, a control station, a police station and utility rooms. The social rooms of the FRU are located on the upper floor above the garages. The garage hall is about 45 m in area. The height of this room is about 5 m. There are 8 vehicles in the garage and hangers for the firefighters’ special clothes.
The fire station is ventilated by a compulsory mechanical system that opens doors on departure/arrival and, if needed, opens windows. Smoking is prohibited in the entire area of the fire station. During the sampling, records of potential emission sources were recorded (vehicle arrivals/departures, vehicle and equipment maintenance, exercises, etc.).
2.2. PM Sampling
Optical and gravimetric measurements were performed simultaneously. Measurements were carried out in the fire station garages from August to December 2021, 10 times every month. Each 24 h long air test started in the morning at shift change and finished the next morning. For optical tests (PM1, PM2.5, PM4, PM7, PM10 and TSP), the particulate matter monitor Met One Aerocet LS 531 was used. The device was programmed to repeat 1 min measurements every 15 min. In the methods based on optical detection, aerosol particles are illuminated by a light beam, which scatter this light in all directions. Some of this light is absorbed at the same time. The difference between the incident and the transmitted light is converted into an electrical signal and recorded in the meter’s memory.
In the gravimetric method, all PM samples were collected within 24 h in the garage of the fire station after the day the firefighters had participated in a firefighting operation. PM sampling was carried out simultaneously using two GilAir-3 personal aspirators: one with a respirable fraction (PM4) collection head, and the other with an inhalable fraction (TSP) collection head. The airflow was 2 L/min for TSPs and 2.2 L/min for PM4. Glass filters with a diameter of 25 mm were placed in the heads, on which PM4 or TSP particulate matter was deposited, depending on the mounted head. Before the measurements, the filters were conditioned for 48 h at 22 °C and 38% humidity and weighted. After PM collecting, filters were again conditioned and weighted.
PM gravimetric sampling in the garage was performed at the same time as the optical measurement method.
Health legislation does not include demands for particles above 10µm, whereas the exposure to PM in the occupational environment is based on the concentration of particles not larger than 4 µm [
46,
47,
48,
49]. For this reason, our studies took into account PM4. TSP are not considered a health risk factor as they are filtered out through the nose and throat. However, TSP cover the full range of particle sizes including PM10, PM7, PM4, PM2.5 and smaller, which pose hazards such as severe respiratory and circulation problems; therefore, they were also included in our research.
2.3. Chemical Analysis
The PAH fractions were extracted from 88 filters by ultrasonification with dichloromethane three times for a total of 45 min. The obtained extract was cleaned up using a column with sodium sulfate, activated silica and activated alumina. The final extracts were concentrated under a helium stream.
Chemical characterization of the collected PM samples was performed to determine the concentration of PAHs by the GC/MS method. The apparatuses used for gas chromatography with mass spectrometry analysis were the Agilent GC 6890A and MS 5973. For the separation of the compounds, an HP–5ms (5%-phenyl)-methylpolysiloxane column that is 30 m × 0.25 mm and 0.15 μm was used. The injection volume was 2.0 µL and the injector temperature was 275 °C. The GC oven temperature program started from 50 °C (hold 1 min) and went to 150 °C at 25 °C/min; next, it went from 150 °C to 280 °C at 5 °C/min (hold 9 min). The carrier gas was helium with a flow of 1.4 mL/min.
For the analysis, selective ion monitoring (SIM) mode was used. An external standard (M–610A, AccuStandard Inc., New Haven, USA) was used in every analysis. The external standard mixture also included the compounds in the internal standard. Possible sample losses that occurred in the evaporation or the other phases of the sample handling were managed by using the relation of the response factors of a native compound and a deuterated compound analyzed in the external standard mixture in the quantitative analysis. Recoveries of PAH internal standards were 78 ÷ 92%. Limits of detection (LOD) and limits of quantification (LOQ), calculated as three times the standard deviation for the blanks, were 0.005 ppb and 0.015 ppb, respectively. PAH concentration in blanks was below the detection limit for all targeted compounds.
2.4. Health Risk Analysis
Health risk assessment was performed based on the 15 PAHs listed as priority by the US EPA [
50]. Their carcinogenic potency was estimated as toxic equivalency factors (TEFs), of which the values are specified in
Table 1. To evaluate the toxicity and assess the risks of a mixture of structurally related chemicals, the toxicity or toxic equivalent (TEQ) of the carcinogenic PAHs can be determined for each day by multiplying the concentration of the individual PAH (C
PAHn) with its toxic equivalent factor (TEF
PAHn); values given by the US EPA were chosen for calculations [
3]:
The obtained TEQ values depend not only on the concentration of pollutants but also on the adopted TEF coefficients, which may have the values presented in
Table 1. The toxicity equivalent (TEQ) was calculated by adding together the TEQ values obtained for the individual PAHs.
Additionally, the incremental lifetime cancer risk (ILCR) and the non-cancerogenic hazard quotient index (HQ) from PAH inhalation over the period of professional activity (Equations (2) and (4), respectively) were calculated [
54,
55].
EC is the exposure concentration, UR is the cancer inhalation unit risk (8.7 × 10
−2 µg/m
3 [
56]), C is the PAH concentration, ED is exposure duration in years, EF is exposure frequency in days/year, AT is the number of days over which the exposure is averaged, EDI is the estimated daily intake of PAHs, IR is the inhalation rate (16 m
3/day), RfD is the reference and BW is body weight (75 kg). Due to the fact that occupational exposure is investigated, a 4 h period of exposure to PAHs lasting 3 days a week (EF—26 days) for 20 years of work (ED) was assumed (a firefighter spends only part of the working day in a garage). For the calculations, life expectancy was assumed to be 70 years (AT).
2.5. Calculations and Data Analysis
Statistical analysis was performed. For data evaluation and presentation, the basic statistical functions of mean, minimum and maximum values of obtained results were used. Additionally, factor analysis was applied to interpret results and explain variations in the data. Median values of individual and Σ-PAHs were compared to calibration curves including standards of analyzed PAHs. The correlation coefficients for the concentration range ranged from 0.98 to 0.99. Statistical significance was defined as p ≤ 0.05.
4. Conclusions
Our study presents the results of occupational exposure to PM and PM-bound PAHs for firefighters in the workplace when performing tasks other than firefighting or rescue operations. The obtained data on the PM fractions and PAH concentrations indicate the existing occupational exposure of firefighters due to bad air quality in fire stations. The occupational exposure of firefighters was assessed in an urban–rural commune, where outdoor air pollution is relatively low and the number of departures was small compared to large cities and highly urbanized areas. The conducted research allows identifying several problems impacting the air quality in garages of fire brigades. One of them is the introduction to a firehouse of contamination deposited on vehicles, equipment and clothes of firefighters. Particles present on the surface of vehicles, equipment, clothes and flooring could be resuspended as a result of the movement of people during the maintenance of PPE or technical rescue equipment. This phenomenon is related, among others, to the number of departures and arrivals of the crew while on duty, which causes a temporary increase in the PM concentrations. Air pollution in the fire brigade unit influenced the occupational exposure of firefighters. Health hazard indices such as the total toxicity equivalent concentration (TEQ), the incremental lifetime cancer risk (ILCR) and the non-cancerogenic hazard quotient (HQ) indicated that firefighters are a group with very high health risk exposure, especially to neoplastic diseases caused by inhalation of carcinogenic PAHs.
Taking into account the significantly increased risk of certain cancers in the professional group of firefighters, research should be continued on the determination of the sources of harmful pollutants, the effectiveness of the methods used to eliminate them, and more accurate and in-depth exposure assessments.