Contamination of firefighter protective clothing by phthalates

2.1 Materials

The study involved two types of firefighter protective clothing, each consisting of a jacket and trousers. Both types of clothing were made from a three-layer material configuration: an outer shell, a middle moisture barrier membrane, and an inner thermal barrier layer. The two types of firefighter protective clothing, designated as A and B, differed in terms of the composition of the materials used (Table 1).

2.2 Use procedure for firefighter protective clothing

Prior to testing, firefighter protective clothing was subjected to preliminary use under controlled conditions in a fire training chamber. The clothing was deployed during training drills at the Firefighting Academy of Warsaw Training Base for Testing Grounds and Rescue Innovation in Nowy Dwór Mazowiecki. Two items of protective clothing were provided for use, including one item fabricated from a material configuration designated as A and one item from a material configuration designated as B (Figure 1).

Figure 1

Photographs of firefighter protective clothing type B after use in a live-fire training simulator (a – jacket, b – trousers).

The firefighter protective clothing was worn on ten occasions, exposing it each time to smoke and chemical emissions from fires, notably those involving chipboard and furniture materials. Each fire event lasted between 40 and 120 min. Following each use, the clothing was washed using a water-based process in accordance with the manufacturer’s recommendations.

2.3 Cleaning procedure for firefighter clothing after multiple uses

Water-based washing of firefighter protective clothing was conducted in accordance with the maintenance protocol outlined in the user manual supplied by the manufacturer. The process employed a specialized laundry machine, Touch Plus Control (Fagor, Poland). The washing temperature for clothing made from two types of material systems (configuration A and type B) was uniform, set at 60°C. The total duration of the washing cycle was approximately 50–60 min. Drying was conducted at a consistent temperature of 60°C using a TS4175 WW cabinet dryer (Electrolux, Sweden), with a drying time of 180 min.

The washing agents used in our procedure were identical to those used by the participating fire and rescue units. They consisted of a detergent specifically formulated for use with the washing equipment and, at the same time, firefighter protective clothing. All these specialized detergents were produced by a single company.

To minimize cross-contamination:

1. each garment was washed separately in the washing machine;

2. each garment underwent washing in the same machine;

3. the washing machine was cleaned between washing cycles for different garments by conducting a standard washing cycle;

4. directly prior to each washing cycle, an empty run was performed using water and washing agents.

2.4 Sampling procedure

Samples were cut from protective clothing items that had been worn ten times and exposed to harmful chemical substances, both before and after washing. For these two variants, three sets of samples were cut from the protective clothing element after use (before washing) and after the last tenth washing. A single set of samples consisted of three samples of the following layers: an outer shell, a middle moisture barrier membrane, and an inner thermal barrier layer. The dimensions of the samples were 0.02 m × 0.02 m. Additionally, tests on new protective clothing were conducted for an additional item of protective clothing. The total number of individual samples was 54 (18 for new clothing, 18 for clothing after use before washing, and 18 for clothing after washing). The study on clothing after use and washing was performed on separated clothing elements such as trouser legs (right and left components). The right-side elements were used for sampling from the worn (contaminated) protective clothing, while the left-side elements underwent a washing process according to the manufacturer’s instructions (Figure 1). Samples for analysis were cut from areas above the knee in trousers.

To prevent damage during washing, protective clothing elements were hemmed with an overlock machine before the washing process and then reinforced with a lockstitch for added strength.

2.5 Chemicals

The following reagents were used in the study: acetonitrile, dichloromethane (J. T. Baker, USA), MilliQ ultrapure water (Millipore, Germany), and a collection of certified PAE standards – EPA 506 Phthalate Esters Mix, which included a concentration of 1,000 µg mL⁻¹ of a six-phthalate standard (Sigma-Aldrich Supelco, USA).

3.1 Determination of PAEs

3.2 SEM analysis

The surface morphology of the samples was examined using a Hitachi SU8010 (Hitachi, Japan) cold field emission scanning electron microscope (FE-SEM). Observations were conducted at an accelerating voltage of 5 kV with a magnification of ×50. To prepare the samples for surface analysis, they were vacuum-coated with gold to improve surface conductivity using a Quorum Technologies Q150ES sputtering device operated under a protective argon atmosphere at a pressure of 0.3 bar. Additionally, nitrogen was introduced to purge the sputtering chamber, facilitating a clean and stable environment for the coating process.

3.3 FTIR analysis

FTIR analysis was performed using a system consisting of an IRSpirit FTIR spectrophotometer equipped with a single-reflection attenuated total reflectance (QATR-S) accessory for direct measurement of solid samples and LabSolutions IR software used for instrument control and data analysis (Shimadzu Corporation Analytical & Measuring Instruments Division, Japan). FTIR spectra were recorded for each sample at three randomly selected locations in the wavenumber range from 4,000 to 500 cm⁻¹.

For FTIR analysis, samples were cut from firefighter protective clothing of types A and B. Tests involved new membrane samples after ten uses (before the tenth washing cycle) and after the tenth washing cycle.

3.4 Statistical analyses

The resultant PAE concentration data were subjected to statistical analysis using Statistica version 10.0 software (StatSoft, Poland).

Statistical analysis of the study results was conducted to assess the significance of the impact of material configuration type on the total phthalate concentrations and the effectiveness of the washing process.

Measurable variables (phthalate concentration and washing effectiveness) were characterized using the mean, standard deviation, and median, as well as minimum and maximum values.

To examine the significance of differences between two groups (independent samples), the following tests were used:

• t-test – when the conditions of normal distribution and homogeneity of variance were met,

• Cochran-Cox test – when the condition of normal distribution was met but the condition of homogeneity of variance was not.

The statistical significance threshold was set at α = 0.05. Results were deemed statistically significant if the probability value was p ≤ 0.05.

Detailed statistical analysis values are presented in Supplementary Materials (Tables S4–S6).

4.1 Phthalate content in contaminations of firefighter protective clothing

Chemical analysis of contaminations in firefighter protective clothing revealed phthalates (PAEs) in all material layers (outer fabric, membrane, and internal thermal barrier) after repeated use (Figures 2 and 3). Among the six compounds analyzed, the presence of BBP, bis(2-ethylhexyl) phthalate, DBP, and DNOP was pronounced; these substances are classified as category 3 or 1 endocrine-active substances.

Figure 2

Concentrations of individual PAEs in knee samples from three layers of firefighter protective clothing type A after ten uses during live-fire enclosure training and ten washing cycles (error bars indicate standard deviations).

Figure 3

Concentrations of individual PAEs in knee samples from three layers of firefighter protective clothing type B after ten uses during live-fire enclosure training and ten washing cycles (error bars indicate standard deviations).

Analysis of the study results indicates that for firefighter protective clothing made from two different material configurations (A and B), the influence of the type of configuration used and the resultant material composition on the concentrations of individual phthalates varied by the material layer (fabric, outer, membrane, and thermal barrier). For the outer fabric and internal thermal barrier, higher phthalate concentrations were observed in configuration B (Figure 4). Conversely, for the middle membrane layer, a higher phthalate content was noted in configuration A (Figure 2).

Figure 4

Washing effectiveness for total PAEs across the three layers of firefighter protective clothing (outer shell, membrane, and thermal barrier).

Considering the function of the material, the highest concentrations of individual phthalates were determined in the middle layer of the material configuration – the moisture barrier membrane. Prior to washing, concentrations of individual phthalates in the membrane of material configuration A (clothing A) reached up to 313 µg g⁻¹ for bis(2-ethylhexyl) phthalate (Figure 2), while in the membrane of configuration B, concentrations of the same phthalate were approximately 20 µg g⁻¹ (Figure 3). Lower concentrations, reaching up to 10 µg g⁻¹, were recorded for all other phthalates in the thermal barrier of material configuration A and in both the outer fabric and thermal barrier of configuration B.

The final, tenth water washing cycle of the protective clothing, which had been frequently used in training chambers, revealed that four or five of the six phthalates studied were still present, depending on the type of material configuration used. It was observed that protective clothing subjected to ten full cycles of use and washing exhibited varying phthalate concentrations based on the material configuration employed in its manufacture (Figures 2 and 3).

For the outer fabric, elevated phthalate concentrations were observed in the external material of configuration B (clothing B), with the content of BBP, bis(2-ethylhexyl) phthalate, and DBP being 11.1, 10.8, and 10.8 µg g⁻¹, respectively (Figure 3).

For the middle layer, the vapor-permeable membrane, it was observed that, irrespective of the material configuration used, completing ten washing cycles did not result in significant changes in phthalate concentrations. Similarly, less favorable outcomes were recorded for material configuration A compared to pre-washing. Concentrations of bis(2-ethylhexyl) phthalate, DNOP, BBP, and DBP in the membrane from configuration A were several times higher (from 2 to 7 times) than those in the membrane from configuration B (Figures 2 and 3). The largest observed discrepancy, a sevenfold difference, was recorded for DNOP: 148.2 µg g⁻¹ in the membrane of configuration A compared to 20.4 µg g⁻¹ in the membrane of configuration B. Furthermore, it was observed that for the membrane of material configuration A, the concentrations of di-n-butyl and DNOPs were higher after washing than before. This suggested the occurrence of secondary membrane contamination.

Following the completion of the tenth washing cycle of firefighter protective clothing, the internal thermal barrier layer exhibited phthalate concentrations at levels comparable to those before washing. The differences were minimal, below 0.5 µg g⁻¹, and this was observed in both material configurations A and B (Figures 2 and 3).

Alexander and Baxter [11] conducted studies on the chemical content of firefighter protective clothing after use in fires, specifically focusing on phthalates among other contaminants [11]. They used jackets (sleeves and hoods) and gloves from firefighter protective clothing for their research, extracting chemicals using methylene chloride and analyzing them using the EPA 8270 method for semi-volatile contaminants, including 20 PAHs and 6 phthalate esters. Their findings indicated that 22 chemical substances were detected in at least 1 sample of clothing. Notably, di-(2-ethylhexyl) phthalate (DEHP), a plasticizer added to polyvinyl chloride to enhance flexibility, was identified in every sample, with the highest concentrations found in hood material (340 µg g⁻¹) and sleeve material (220 µg g⁻¹), which were 52–875 times higher than any measured PAH. Similarly, the current study also found high DEHP levels in firefighter protective clothing materials, particularly in the middle layer (membrane) of clothing type A after ten uses and before the tenth wash, where DEHP concentrations reached nearly 320 µg g⁻¹. These measurements suggest that firefighters were exposed to high levels of DEHP, a probable carcinogen to humans, significantly above most of the previously studied levels [11,15]. Therefore, firefighters’ exposure to phthalate esters warrants further investigation, as exposure to semi-volatile organic compounds could occur through inhalation or by deposition on equipment and clothing, which subsequently contacts the skin, posing a risk of dermal absorption. Given their highly lipophilic nature, Alexander and Baxter [11] suggested that phthalate diesters could be readily absorbed through the skin, especially under the elevated temperatures typical in firefighting scenarios.

Poutasse et al. [17] tested the developed markers for assessing chemical exposures of firefighters. They conducted concentration tests of harmful chemicals, including phthalates, to determine the effect of duty time, number of calls, and firefighter rank on exposure to chemicals. The results showed that concentrations of individual phthalates were usually higher in markers used during duty compared to those used off duty. This included phthalates analyzed in our study, such as DEHP and DBP, as well as others like DIBP, di-n-nonyl phthalate, and guaiacol. The highest concentration, similar to our findings, was recorded for DEHP, at approximately 550 nmol g⁻¹ for markers used by firefighters off duty and about 950 nmol g⁻¹ for markers used on duty. Comparing with our results, it was observed that DEHP was also present in protective clothing materials for firefighters in large quantities (11.23 µg g⁻¹, outer shell clothing A before washing). Poutasse et al. [17] concluded that phthalate concentrations increased slightly with years spent in the fire service, which was also visible for PAHs. Therefore, prolonged firefighting service may increase exposure to chemicals.

Research has also been conducted on other chemicals released during fires. A study on the occupational hazards of firefighters in Great Britain related to carcinogenic substances released during fires was conducted by Stec et al. [18]. Samples for testing were taken from the skin surface (jaw, throat, and hands), personal protective equipment, and the work environment (office and fire station). A group of 16 PAH compounds (including benzo(a)pyrene, and 7,12-dimethylbenz(a)anthracene) were determined in materials before and after 60 min of exercises in a shipping container. PAH concentrations, similar to those of phthalates, were high, reaching a maximum of 2,000 mg m⁻² for clothing and 6,000 mg m⁻² for masks.

4.2 Influence of clothing type on total phthalate concentration

Studies have demonstrated a varied influence of material composition on the determined total concentration of the analyzed phthalate group in clothing materials worn in a live-fire training simulator. For configuration A, considerably higher phthalate concentrations were observed in the membrane (548 µg g⁻¹; Table 3). For configuration B, the total PAE concentration was about eight times lower (69 µg g⁻¹). Statistical analysis showed significant differences (p = 0.0120). Meanwhile, configuration B materials exhibited a higher phthalate level in the outer shell (38 µg g⁻¹) compared to configuration A materials (p = 0.0001). The fabric configuration did not affect total phthalate content in the internal layer of protective clothing, i.e.`, in the thermal barrier, where, regardless of the fabric type and composition, comparable amounts were accumulated (32–33 µg g⁻¹). In this case, statistical analysis did not show any significant differences (p = 0.6948).

It was observed that the process of washing firefighter protective clothing after use had minimal impact on the total phthalate content across nearly all the material layers (outer shell, membrane, and thermal barrier), regardless of the material configuration used (A or B). A notable exception occurred in the membrane of configuration A, where total phthalate concentration substantially decreased from 548 to 275 µg g⁻¹ after ten washing cycles. For the remaining materials in both configurations, no significant reduction in phthalate concentration was observed post-washing (Table 3).

In the case of the outer shell of material configuration A, characterized by a twill weave, the total PAE concentration was about 7–8 times lower, both before and after washing, compared to the concentration determined for the outer shell of configuration B with a plain weave (Table 3). In the case of thermal barriers, the type of weave was the same (plain), but it was not important because total PAE concentrations were similar for material configurations A and B.

Research conducted by Rabajczyk et al. [19] on the sorption of another group of chemicals, 18 PAHs, in firefighter protective clothing materials showed the highest total concentration of 2.11 µg g⁻¹ in samples taken from the armpit area of the jacket and from the buttock area of the trousers. The lowest total PAH concentration of 0.01 µg g⁻¹ was found in gloves, the inner cuff of the forearm, and trousers (samples taken from the thigh). It was observed that the distribution of PAH concentrations was uneven in the case of the jacket and trousers made of aramid fibers. The total PAH concentrations determined by Rabajczyk et al. [19] were much lower than those in our case, which reached several hundred µg g⁻¹. What was noticeable here was the influence of the type of chemicals accumulating in firefighter clothing, as well as the amount of exposure to chemicals.

The materials employed in the various configurations varied in composition (membrane and lining) or fiber type (outer fabric). The outer fabric of configuration B comprised 58% para-aramid, 40% polybenzimidazole (PBI), and 2% antistatic fiber, whereas the outer fabric of configuration A contained a significantly higher proportion of meta-aramid fibers (98% meta-aramid and 2% antistatic fibers; Table 1). The reduced aramid fiber content in the outer fabric of configuration B, alongside the presence of PBI fibers, may have contributed to greater absorption of hazardous chemical substances. The surface mass of both outer fabrics A and B was comparable, at 210 and 205 g m⁻², respectively.

Among a plethora of aromatic polyamides, (para-)aramid fibers are particularly notable for their practical application and significance. Constructed from linear, stiff, and regularly arranged paraphenylene terephthalamide molecular chains, these fibers exhibit a highly structured lattice. The macromolecules of poly-(p-phenylene terephthalamide) are aligned linearly along the axis, forming a highly ordered structural layer interconnected by robust hydrogen bonds. It is the regularity of this semi-crystalline structure that imparts exceptional physico-mechanical properties to para-aramid fibers [20,21]. However, the high chemical stability of the aromatic rings, linked by robust amide bonds, ensures thermal resistance and durability. Meta-aramid fibers PMIA display superior flame resistance compared to para-aramid fibers. In addition, meta-aramid fibers show substantial resistance to a wide range of chemical agents. They withstand most high-concentration inorganic acids and maintain good resistance to alkaline conditions at room temperature. PBI is an organic fiber noted for its flame-retardant properties [20,21].

The membrane incorporated into configuration B also featured a composition with half the amount of meta-aramid and twice the amount of polytetrafluoroethylene (PTFE) laminate compared to other configurations (Table 1). The membrane in configuration B was composed of 25% meta-aramid, 25% para-aramid, and 50% PTFE laminate. In turn, the membrane in configuration A consisted of 50% meta-aramid, 25% para-aramid, and 25% PTFE laminate. The differing proportions of meta-aramid and PTFE laminate in these configurations may have led to a greater accumulation of phthalates in the membrane of configuration A.

The varying concentrations of meta-aramid fibers within the thermal barrier of both material configurations (A and B) did not influence the differential accumulation of phthalates in the clothing materials, nor did they affect the varied removal of chemical substances during the washing process. Similar quantities of phthalates accumulated in the thermal barriers of both configurations. The thermal barrier of configuration A comprised 50% aramid and 50% FR viscose in the lining and 85% meta-aramid with 15% para-aramid in the felt. Conversely, the thermal barrier of configuration B contained a lining of 93% meta-aramid, 5% para-aramid, and 2% antistatic fiber, with the felt consisting of 67% meta-aramid and 33% para-aramid. Both thermal barrier types had comparable surface weight of approximately 170 g m⁻².

4.3 Effectiveness of washing in reducing PAE concentrations

The effectiveness of the washing process in reducing PAE concentrations was quantified for the three distinct layers of protective clothing (outer shell, membrane, and thermal barrier) using the following equation [15]:

where c ₀ is the PAE concentration in pre-wash samples and c ₁ is the PAE concentration in post-wash samples.

The effectiveness of washing was computed separately for each PAE, with consideration given to the type of clothing and the composition of the materials used.

Research demonstrated that, as a result of washing, phthalates were removed to a low or moderate extent from the various materials of firefighter protective clothing that had been subjected to multiple uses (Figure 4). For configuration A materials, washing effectiveness for samples collected from the knee area was 32% for the outer shell, 48% for the membrane, and 10% for the thermal barrier. On the other hand, washing effectiveness for configuration B materials showed substantially lower rates, with 0.7% for the outer shell, 2.3% for the middle membrane, and a negative 0.3% for the thermal barrier.

Under identical conditions of firefighter protective clothing use in a training chamber, a higher washing effectiveness was observed for configuration A materials compared to configuration B. Due to the large variation in results for the outer shell and thermal barrier, the differences in washing effectiveness for configurations A and B were not significant (p-values of 0.1448 and 0.1998, respectively). Statistical analysis confirmed the significance of differences between configurations A and B only for the membrane (p = 0.0051). The highest washing effectiveness was recorded for the membrane layer in both configurations A and B, ranging from 2% in configuration B to 48% in configuration A. This variability was also noted in the effectiveness of phthalate removal from the outer shell and thermal barrier in configurations A and B (Figure 4). Washing effectiveness for the outer shell varied from 1% in configuration B to 32% in configuration A (Figure 4). For the thermal barrier, the observed washing effectiveness ‎was the lowest, ranging from −0.3% (configuration B) to 10% (configuration A). In one case, potentially due to secondary contamination of the thermal barrier in configuration B, a negative washing effectiveness (−0.3%) was recorded.

The authors attribute the variability in washing effectiveness for protective clothing material configurations A and B to the differing responses of these materials during the washing process.

The outer shell of configuration A (Figure 5b and h), after use in an exercise chamber by firefighters and ten washing cycles, showed a smaller degree of deterioration (number of torn fibers) compared to the outer shell in configuration B (Figure 6b and h), which was especially visible under ×1,000 magnification. In both configurations of firefighter protective clothing materials in new condition, an almost perfect membrane without any creases was observed. However, numerous creases appeared following use and the washing process. A loosening of the weave was also observed, characterized by larger pores than those present before the washing process (Figures 5d and j and 6d and j).

Figure 5

SEM images of firefighter protective clothing materials in configuration A: (a and g) new outer shell; (b and h) outer shell after ten uses and washing; (c and i) new membrane; (d and j) membrane after ten uses and washing; (e) new thermal barrier; and (f) thermal barrier after ten uses and washing. Magnification: ×50 (a–f) and ×1,000 (g–j).

Figure 6

SEM images of firefighter protective clothing materials in configuration B: (a and g) new outer shell, (b and h) outer shell after ten uses and washing, (c and i) new membrane, (d and j) membrane after ten uses and washing, (e) new thermal barrier, and (f) thermal barrier after ten uses and washing. Magnification: ×50 (a–f) and ×1,000 (g–j).

It was observed that degradation of the material structure did not contribute to higher washing effectiveness. The outer fabric, membrane, and thermal barrier of configuration B exhibited greater damage during use and washing, along with significantly lower effectiveness in phthalate removal.

Considering the foregoing, the authors posited that the composition and fabrication methods of materials used in both configurations A and B could influence the level of phthalate removal during washing. The study demonstrated that configuration A materials ‎were more amenable to removing phthalate compounds accumulated on their surfaces, thereby facilitating higher washing effectiveness.

Figures 7 and 8 show representative FTIR spectra for membranes used in material configurations A and B. The FTIR spectra reveal characteristic absorption bands corresponding to the structural components of the membrane used, namely aramid polymers and PTFE. The obtained spectroscopic data were consistent with previously reported results, particularly those presented by Khandare [22] and Kobayashi et al. [23].

Figure 7

FTIR spectra for the membrane in material configuration A (N, new membrane; 10U, after ten uses; 10 W, after ten washing cycles).

Figure 8

FTIR spectra for the membrane in material configuration B (N, new membrane; 10U, after ten uses; 10 W, after ten washing cycles).

Comparative analysis of the FTIR spectra for the membrane in various use conditions indicates changes in band intensities and slight shifts in characteristic peaks. These variations can be interpreted as evidence of phthalate adsorption on the surface or within the structure of the membrane material. Notably, significant changes were observed in the spectral range of 2,810–3,010 cm⁻¹.

For membrane A, two absorption bands at 2,970 and 2,980 cm⁻¹, which are typically assigned in the literature to ═C–H stretching vibrations in aromatic rings (characteristic of aramid polymer structures) disappeared after ten uses (Figure 7). The disappearance of these bands may indicate partial coverage or chemical modification of the existing functional groups due to phthalate adsorption or the presence of other organic compounds in the working environment. In contrast, the appearance of a new band at 2,960 cm⁻¹ in membrane B can be attributed to the presence of –CH₃ or –CH₂– groups, associated with the alkyl chains of phthalate compounds (Figure 8).

Although laundering leads to a slight decrease in the intensity of the aforementioned bands, it does not result in their complete removal. This suggests that phthalates may form relatively stable physicochemical interactions with the membrane material. This could be due to both surface adsorption and the diffusion of phthalates into the polymer structure at the molecular level, which significantly hampers their removal under standard washing conditions.