Exposure to airborne ultrafine particles from cooking in Portuguese homes

Abstract

Cooking was found to be a main source of submicrometer and ultrafine aerosols from gas combustion in stoves. Therefore, this study consisted of the determination of the alveolar deposited surface area due to aerosols resulting from common domestic cooking activities (boiling fish, vegetables, or pasta, and frying hamburgers and eggs). The concentration of ultrafine particles during the cooking events significantly increased from a baseline of 42.7 μm²/cm³ (increased to 72.9 μm²/cm³ due to gas burning) to a maximum of 890.3 μm²/cm³ measured during fish boiling in water, and a maximum of 4500 μm²/cm³ during meat frying. This clearly shows that a domestic activity such as cooking can lead to exposures as high as those of occupational exposure activities.

Implications:

The approach of this study considers the determination of alveolar deposited surface area of aerosols generated from cooking activities, namely, typical Portuguese dishes. This type of measurement has not been done so far, in spite of the recognition that cooking activity is a main source of submicrometer and ultrafine aerosols. The results have shown that the levels of generated aerosols surpass the outdoor concentrations in a major European town, which calls for further determinations, contributing to a better assessment of exposure of individuals to domestic activities such as this one.

Introduction

Indoor air quality has become a very important issue in recent years, as most people spend more than 80% of their time indoors (NRC, 1981). Considering domestic activities, cooking represents one of the most significant particle generation activities in household facilities (Buonanno et al., 2009; Kamens et al., 1991; Ozkaynak et al., 1996). In addition, ultrafine particles (UFP) emitted from cooking activities have also been associated with several respiratory diseases (Wallace et al., 2004). The adverse health effects of ultrafine particulate matter have been reported in numerous scientific studies (Buonanno et al., 2010; Pope, 2000). A number of epidemiological studies showed that adverse health effects are attributed not only to the size of UFP, but also to PM_2.5 (Pope and Dockery, 2006) and PM₁₀ (Loomis, 2000) particle size, as well as other factors such as UFP concentration number (Hauser et al., 2001), surface area (Driscoll, 1996), and overall exposure rate (Siegmann and Siegmann, 1998). Furthermore, Anastacio and Martin (2001) suggest that health effects from airborne particles are strongly associated with coexposure with other airborne pollutants, as particles can act as condensations nuclei for other hazardous airborne substances. Several studies have suggested that, considering similar mass concentrations, nanometer size particles can be more harmful than micrometer-size particles (Oberdorster, 2001; Oberdörster et al., 1995; Seaton et al., 1995), which can be due to the facts that the number of particles and particle surface area per unit mass increases with decreasing particle size and that pulmonary deposition increases with decreasing particle size. Therefore, the dose by particle number or the surface area will increase as the particle size decreases (Ramachandran et al., 2005).

Nanosized particles can enter the body via three main routes: (a) inhalation, (b) ingestion, and (c) dermal penetration. The detrimental health effects of inhaling fine aerosols were recognized long ago, and various attempts have been made to minimize exposure, such as the issuing of specific regulations on emissions and objectives for air quality. Current workplace and ambient air environmental exposure limits, which were established long ago, are based on particle mass. However, this criterion does not seem to apply when referring to nanosized particles, as these are, in fact, characterized by having very large surface areas, which has been pointed out as a distinctive characteristic that could even turn an inert substance into a toxic one, having the same chemical composition but exhibiting very different interactions with biological fluids and cells (Driscoll, 1996). Thus, a growing number of experts (Donaldson et al., 1998; Ramachandran et al., 2005) have claimed that surface area should be used for nano sized particle exposure and dosing. As a result, assessing workplace conditions and personal exposure based on the measurement of particle surface area is of increasing interest. If ultrafine particles can be deposited in the lung and remain there, and also have an active surface chemistry and interact with the body, then there is a considerable potential for exposure and dosing. The potential for adverse health effects is directly proportional to particle surface area (Driscoll, 1996). Regarding domestic activities, some previous studies were focused on the determination of fine particles concentration, expressed as number per cubic centimeter, in Espoo, Finland (Hussein et al., 2006), in Helsinki, Athens, Amsterdam, and Birmingham (Hoek et al., 2008), and in Windsor, Ontario, Canada (Kearney et al., 2011). However, none of these studies comprised the determination of surface area of indoor particles. Concerning indoor activities, several studies have attempted to measure the particle number concentration and size distribution of particles during cooking (Buonanno et al., 2009; He et al., 2004; Hussein et al., 2006; Li et al., 1993; Wallace et al., 2004). These studies provided valuable information on the characteristics of particles generated by different cooking methods. Among them, He et al. (2004) quantified the emissions of indoor particle sources in 15 houses in Brisbane, Australia, and found that indoor activities resulted in an increase of particle number concentration by 1.5–27 times the baseline concentrations, while Wallace et al. (2004) found out that cooking episodes (mostly frying) taking place on a house in Washington, DC, produced particles to the magnitude of 10¹⁴ after only 15 min of cooking, and more than 90% of the particles were in the ultrafine range. Buonanno et al. (2009) determined emission factors for cooking selected Mediterranean food using gas and electric stoves and discussed the observed difference; See and Balasubramanian (2008) analyzed the chemical characteristics of particles emitted during cooking activities, while Dennekamp et al. (2001) discussed the size and number of particles generated during cooking using gas and also electricity. Several studies have been done previously regarding emissions from cooking events, such as meat charbroiling, but these studies have been focused mainly on the determination of organic compounds emitted from these operations taking place outdoors, and on their influence on ambient air of cities (Mohr et al., 2009; 2011; Rogge et al., 1991; Schauer et al., 2002). Only the studies of Rogge et al. (1993) and Hildemann et al. (1991) determined the size distribution of particles emitted during meat frying, which was found to be in the range of 0.2–1 μm.

Regarding the assessment of exposure to nanoparticles, previous studies (Fissan et al., 2007) showed instruments such as a nanoparticle surface area monitor (NSAM), which is an instrument designed to measure airborne surface area concentrations that would deposit in the alveolar or tracheobronchial region of the lung. It was found that this instrument can be reliably used for the size range of nanoparticles between 20 and 100 nm, and also that the upper size range can be extended to 400 nm, where the minimum in the deposition curve occurs (Asbach et al., 2009). In fact, the size fraction below 20 nm usually contributes only negligibly to the total surface area and is therefore not critical. On the other end, a preseparator is needed to remove those particles above 400 nm. Particle material does not seem to have a noticeable impact, either on particle charging in the NSAM or on the deposition curves within the aforementioned size range, but particle hygroscopicity can cause the lung deposition curves to change somewhat, which cannot be mimicked by the instrument. It was also found that the tendencies of the particle deposition curves of a reference worker for alveolar, tracheobronchial, total, and nasal depositions share the same tendencies in the 20–400 nm size range and that their ratios are almost constant. By means of appropriate calibration factors, the NSAM can be used to deliver the lung deposited surface area concentrations in all these regions, based on a single measurement (Wilson et al., 2007). Therefore, NSAM equipment can be reliably used to supply information on the deposited surface area of UFP particles.

Also, it has been noticed that an important information gap that limits the use of data for epidemiological studies and quantitative risk assessment evaluations is the absence of quantitative exposure data from which to estimate the dose-response relationship (Mauderley, 1992), which is particularly true when referring to UFPs. Therefore, the main aim of this study is to assess exposure of individuals, based on surface area of generated aerosols, during the usual preparation of typical Portuguese domestic meals.

Materials and Methods

Sampling site

The experimental campaign was conducted in June 2011, in the actual kitchen of a mid-level (sixth floor) flat located in the center of Lisbon, Portugal. No mechanical ventilation was used during the study and the doors and windows were closed during all measurements, and it is considered that this campaign was not significantly affected by outdoor levels. Nevertheless, the baseline concentration indoors was always measured when cooking activities were not taking place. During measurements, the indoor kitchen temperature ranged from 19 to 21°C, no individuals were present except for the investigator, and no human activities were taking place in the house other than cooking in the kitchen. The kitchen has dimensions of 7.2 × 3 × 2.5 m, with counters 0.50 × 0.60 m facing walls, as depicted in Figure 1. The height of the bench from the floor is 0.85 m, and the sampling probe was located 20 cm above the stove, close to the breathing zone of the cook, as shown in Figure 2. The stove, which was the only potential source of particles present, was a TEKA SLP60 3G1P gas stove with one electric station (not used) and three natural gas stations, as shown in Figure 3. From those only two gas stations (numbers 1 and 3) were used at full power, 1500 W and 600 W, respectively. Above the stove there was a ventilation hood, which was not operating during measurements.

Figure 1. Layout of the residential kitchen.

Figure 2. Location of sampling probe.

Figure 3. Aspect of gas stove showing used stations for cooking.

Instrumentation

For estimating ultrafine particle exposure a nanoparticle surface area monitor (NSAM), TSI model 3550, was used, in alveolar mode. This equipment indicates the human lung-deposited surface area of particles expressed as square micrometers per cubic centimeter of air (μm²/cm³), corresponding to tracheobronchial (TB) or alveolar (A) regions of the human lung, according to the ICRP deposition model developed by the American Conference of Governmental Industrial Hygienists (ACGIH) (Phalen, 1999). This equipment is based on diffusion charging of sampled particles, followed by detection of the charged aerosol using an electrometer (Fissan et al., 2007). Using an integral pump, an aerosol sample is drawn into the instrument through a cyclone with a 1-μm cut point. The sample flow is split, with one stream going through a set of carbon and HEPA filters and an ionizer to introduce positively charged ions into a mixing chamber. The other aerosol flow stream is mixed with the ionized stream in a mixing chamber and charged aerosol, and excess ions move onto an ion trap. The ion trap voltage can be set to TB or A response. The ion trap acts as an inlet conditioner or a size-selective sampler for the electrometer, by collecting the excess ions and particles that are not of a charge state, corresponding to the TB or A response settings. The aerosol then moves on to the electrometer for charge measurement, where current is passed from the particles to a conductive filter and measured by a very sensitive amplifier, as shown schematically in Figure 4. The charge measured by the electrometer is directly proportional to the surface area of the particles passing through the electrometer. The equipment was set to alveolar response settings only, as this is the most significant metric.

Figure 4. Schematic showing the operation principle of a NSAM equipment (TSI, 2005).

It should be noted that this equipment does not actually measures total surface area of particles, but rather the surface area expected to be deposited in the lung region, according to the size-specific deposition fraction from the ICRP model (Phalen, 1999).

Execution of measurements

Measurement campaigns reproduced sequential operations for cooking two separate dishes, on the same meal. As the intention of this study is, in fact, to assess exposure of individuals during the usual preparation of typical Portuguese domestic meals, the measuring campaigns mimicked real-life cooking conditions, thus maintaining actual cooking times and also the sequence of operations for preparing a meal for two persons, consisting of a fish and also a meat dish. The measured levels are intended to be representative of the exposure experienced by a cook involved daily in the preparation of this type of domestic meals.

The first dish (fish) consisted of 700 g of cauliflower boiling in 1 L of water for 10 min, 100 g of catfish boiling in 500 mL of water for 20 min, a sauce using 150 g of cream and 50 g of margarine for 13 min by frying in a pan, and 700 g of broccoli boiling in 1 L of water for 15 minutes. The second dish (meat) consisted of frying 100 g of a meat hamburger for 8 min, frying 1 egg for 2 min, and 400 g of spaghetti boiling in 500 ml of water for 10 min. All water boiling used about 15 g of raw salt, and meat was cooked using salt and pepper. In the preparation of meals, two gas stations were used (as described previously) sequentially, and not simultaneously. The fish dish was first prepared at station 1, after which the meat dish was prepared at station 3.

Each measurement sequence was repeated three times. Prior to cooking the meals, a set of measurements was made in order to determine baseline conditions, which comprised no gas flame and no cooking, and also gas flame only but no cooking. These measurements of airborne particles levels produced during the burning of gas flame without the addition of foods were performed as emitted ultrafine particles can be due not only to the cooking operations but also to the gas combustion, as noticed by Dennekamp et al. (2001).

Results and Discussion

Measurement results, expressed as the average of three consecutive cooking operations are presented in Table 1, which also shows calculated values of time-weighted average (TWA) for 8-h periods, total deposited alveolar area, and dose per lung area. Table 1 also shows the total deposited area for the preparation of the whole meal, comprising the two dishes, and the total dose per lung area.

Table 1. Measurement results

Samplingconditions	Average deposited area (μm^2/cm^3)	TWA for 8 hr(μm^2/cm^3)	Total deposited area(μm^2)	Dose per lung area(μm^2/m^2) ^a
Baseline	73 ± 7.4	1.3	6.07 × 10^5	7.59 × 10^3
Boiling cauliflower	230 ± 9.9	9.6	4.60 × 10^6	5.75 × 10^4
Boiling fish	890 ± 38.3	37.1	1.78 × 10^7	2.23 × 10^5
Frying sauce	388 ± 8.3	11.2	5.37 × 10^6	6.71 × 10^4
Boiling broccoli	175 ± 7.5	13.0	6.26 × 10^6	7.83 × 10^4
Frying hamburger	100 ± 4.3	20.5	9.86 × 10^6	1.23 × 10^5
Frying egg	230 ± 10.2
Boiling spaghetti	120 ± 5.2	8.2	3.94 × 10^6	4.92 × 10^4
Total for meal preparation	—	18.8	4.78 × 10^7	5.98 × 10^5
Total for meal preparation discounting baseline	—	18.3	4.72 × 10^7	5.90 × 10^5
Note: ^aConsidering an average lung area of 80 m^2.

Figures 6 to 9 show the measured alveolar deposited surface area (ADSA) for some of the cooking operations described previously, where the occurrence of the cooking events is also depicted in the graphs, as follows. Except for Figure 6, all figures are presented with the scale 0.0–600.0 μm²/cm³ for ADSA. Figure 6 exhibits a peak of 1900 μm²/cm³, and this is why the scale for ADSA ranges from 0.0 to 2000 μm²/cm³. Figure 9 shows a reduced scale of 0.0–600.0 μm²/cm³ (b) and also an expanded scale (a) of 0.0–6000.0 μm²/cm³.

Figure 5. Measurements during baseline showing the evolution of alveolar deposited surface area (ADSA) with time: sample 1 (no cooking, no gas flame); sample 2 (no cooking but gas flame on station 3); sample 3 (no cooking but gas flame on station 1).

Figure 6. Measurements during cauliflower boiling with cooking events marked, showing the evolution of ADSA with time (indicators are described in Table 3).

Figure 5 shows the baseline obtained under three different conditions: (1) no cooking and no gas; (2) no cooking but gas burning in station 3; and (3) no cooking but gas burning in station 1. These measurements were performed sequentially, reproducing the sampling mode during cooking, and the average measured values are presented in Table 2. It can be noticed that gas burning in station 3 results in a small increase from the original baseline, while a more marked increase is observed during gas burning in station 1, which is, in fact, the accumulation from both stations.

Table 2. Baseline determination

	No cooking, no gas burning	No cooking, gas burning in station 3	No cooking, gas burning in station 1
Average deposited area (μm^2/cm^3)	42.7 ± 0.25	46.2 ± 4.39	72.9 ± 7.44
Minimum measured value (μm^2/cm^3)	42.1	42.3	60.5
Maximum measured value (μm^2/cm^3)	43.3	59.4	85.5
TWA for 8 hr(μm^2/cm^3)	0.98	0.91	1.27
Total deposited area(μm^2)	4.70 × 10^5	4.39 × 10^5	6.07 × 10^5
Dose per lung area(μm^2/m^2)*	5.88 × 10^3	5.48 × 10^3	7.59 × 10^3
*Considering an average lung area of 80 m^2.

6–9 show the evolution of ADSA during cooking events as follows:

Figure 7. Measurements during broccoli boiling with cooking events marked, showing the evolution of ADSA with time (indicators are described in Table 4).

Figure 8. Measurements during spaghetti boiling with cooking events marked, showing the evolution of ADSA with time (indicators are described in Table 5).

Figure 9. Measurements during hamburger and egg frying with cooking events marked: (a) expanded scale 0.0 to 6000 μm²/cm³; (b) reduced scale: 0.0 to 600 μm²/cm³, showing the evolution of ADSA with time (indicators are described in Table 6).

1.	Fish dish: (a) cauliflower boiling; (b) broccoli boiling.
2.	Meat dish: (a) spaghetti boiling; (b) hamburger and egg frying.

The exact description of events, depicted in those graphs by numeral indicators, is also presented in 3–6.

Table 3. Sequence of events during cauliflower boiling

Indicator	Time	Cooking phase: cauliflower boiling	ADSA (μm^2/cm^3)
1	18:53	Baseline	73
	18:55	Water and salt added	75
	19:00	Water starts boiling	100
2	19:02	Lid removed and cauliflower added	175
	19:03	Steam emitted entraining particles	1900
	19:04	Lid put onto saucepan	200
3	19:07	Lid partially uncovered	225
4	19:09	Lid removed	600
5	19:12	Heat turned off: cooking ready	850

Table 4. Sequence of events during broccoli boiling

Indicator	Time	Cooking phase: broccoli boiling	ADSA (μm^2/cm^3)
1	19:48	Baseline	30
	19:49	Water and salt added	35
2	19:51	Water starts boiling	70
3	19:56	Lid removed	130
4	19:57	Lid put onto saucepan	110
5	20:04	Broccoli added	190
	20:06	Broccoli boiling	240
	20:17	Broccoli boiling	310
6	20:19	Heat turned off: cooking ready	280
	20:22	After cooking emission (possible coagulation of emitted particles)	360

Table 5. Sequence of events during spaghetti boiling

Indicator	Time	Cooking phase: spaghetti boiling	ADSA (μm^2/cm^3)
	19:34	Baseline	30
	19:35	Water and salt added	35
	19:36	Water starts boiling	40
1	19:37	Spaghetti added	70
2	19:45	Spaghetti boiling	130
	19:53	Heat turned off: cooking ready	120
	19:55	Spaghetti taken out	110
3	20:00	After cooking emission (possible coagulation of emitted particles)	80

Table 6. Sequence of events during cooking of the meat dish

Indicator	Time	Cooking phase: meat dish	ADSA (μm^2/cm^3)
		Baseline	40
	16:10	Margarine and cream added	45
1	16:13	Hamburger starts to fry	45
	16:15	Hamburger frying	50
2	16:18	Hamburger cooked	100
	16:20	Heat is turned off: hamburger removed	100
3	16:51	Heat is turned on	50
	16:52	Egg starts to fry	4500
	16:54	Heat is turned off: egg cooked	110
4	16:55	Egg is removed	160
	17:00	After cooking emission (possible coagulation of emitted particles)	230
	18:00	Baseline levels reached again

Regarding cauliflower boiling (which takes place at station 1), it can be noted that ADSA starts slightly increasing from the baseline value when steam starts to be emitted. However, the ADSA values continue to increase when cauliflower is added to the boiling water and the outcoming steam entrains small particles, resulted in a high concentration peak observed just after indicator 2 (1900 μm²/cm³). After cooking is ready, and the heat is turned off, a decrease on emissions can be observed. However, the boiling of another vegetable (broccoli) exhibits a different emission profile: ADSA increases from the baseline levels after steam emission, but steam does not seem to entrain particles as quickly as in cauliflower boiling. ADSA continues to increase during boiling and even some minutes after the heat is turned off, possibly corresponding to coagulation of emitted particles. Altogether, the ADSA evolution exhibited during broccoli boiling rises more gradually during the whole process, while during cauliflower boiling, very high concentration peaks were noted.

During spaghetti boiling a gradual evolution profile, more similar to broccoli boiling, could be observed. Again, some concentration peaks continue to be observed after heat is turned off, possibly due to coagulation phenomena.

Table 6 describes the cooking events during the preparation of the meat dish, which consisted on hamburger and egg frying. There. Very high concentration peaks were noticed when frying of the meat and egg takes place, reaching a maximum of 4500 μm²/cm³, just after indicator 3 in Figure 9.

Globally, measured ADSA are higher during frying than during boiling, as previously noted by See and Balasubramanian (2008). However, in terms of average values shown in Table 1, boiling fish exhibits the highest value.

It can be noticed that these measurements showed differentiated patterns for the selected cooked dishes, as previously noted by Li et al. (1993) and Buonanno et al. (2009). All the cooking events resulted in the generation of ultrafine aerosols. The generated aerosols result in significant increases from the measured baseline (from 2 to 62 times more, in terms of ADSA), which indicates important exposure levels for person cooking that cannot be regarded only as an occupational hazard, as a considerable percentage of individuals not engaged in professionally preparing food are also exposed in domestic activities.

As previously mentioned, some authors performed studies on the emissions resulting from cooking operations, which were mainly focused on the nature of organic compounds emitted from frying meat and charbroiling in outdoor appliances (Mohr et al., 2009; 2011; Rogge et al., 1991; Schauer et al., 2002). Only Rogge et al. (1993) and Hildemann et al. (1991) measured the size distribution of particles emitted during meat cooking, which was found to be in the range of 0.2–1 μm.

Other authors measured levels of deposited surface area of aerosols in the urban environment of major towns, and found maximum outdoor concentrations ranging from 30 to 45 μm²/cm³ in Dusseldorf, Germany (Kuhlbusch et al., 2004); 38 to 71 μm²/cm³ in Los Angeles, CA (Ntziachristos et al., 2007) ;and 34 to 89 μm²/cm³ in Lisbon, Portugal (Albuquerque et al., 2012). However, it should be noted that the composition of traffic-generated particles (such as gasoline and diesel combustion, metals from brake wear, tire and road surface wear, resuspended dust) is substantially different from cooking particles, which are mainly salt or mineral particles generated from boiling water, oil droplets, and pyrolyzed meat or protein generated during frying. Nevertheless, as some authors pointed out (Schauer et al., 2002), several organic compounds in the range C₁ to C₂₇ can easily result from meat cooking and frying (usually at temperatures somewhat higher than the ones used for cooking in this study), and it is also well known that very fine aerosol particulate, in the range 0.2–1 μm, can act as condensation nuclei for such organic compounds (Mohr et al., 2009). Therefore, a full assessment of the toxicity regarding these generated aerosols must take this into account.

Meanwhile, this study shows that the tested cooking events result in deposited surface areas of aerosols that are considerably somewhat higher than the order of magnitude of measured outdoor levels, which are, of course, highly dependent on automobile traffic. Also significantly high values of total deposited area (4.72 × 10⁷ μm²) and dose per lung area (5.90 × 10⁵ μm²/m²) were determined during the preparation of the whole meal.

It is expected that during cooking the presence of higher humidity and emitted organic vapors tend to induce the smaller aerosols to disappear by coagulation (Li et al., 1993). During the execution of the second meal it was also decided to continue measuring ADSA levels after the cooking event until recovery of the previously observed baseline concentration, in order to obtain an estimation of the recovery rate. This was made calculating the first derivative on the measured curve, as shown in Table 7. The obtained values indicate that increased ADSA verified as a result of each cooking event do not result only in increased instantaneous ADSA but remain in the atmosphere for some time as a result of condensation and agglomeration processes occurring in the nearby atmosphere, as noted also by Li et al. (1993). The recovery rate does not seem to be dependent on the magnitude of the maximum obtained ADSA due to the event, but possibly on the relative size of generated particles (Li et al., 1993).

Table 7. Calculated concentration recovery rate

Sampling conditions	Average deposited area (μm^2/cm^3)	Recovery time until baseline (min)	Recovery rate(μm^2/cm^3 min)
Frying hamburger	100.0	14:30	4.0
Frying egg	230.0	60:00	3.0
Boiling spaghetti	120.0	30:00	1.7

Conclusions

Previous studies (Albuquerque et al., 2012; Fissan et al., 2007; Kuhlbusch et al., 2000; Ntziachristos et al., 2007) confirmed evidence that diffusion chargers are useful and reliable instruments for measuring aerosol concentrations in different environments and that their signal can be combined with the number concentration to provide an estimate of the mean electrical mobility diameter in real time.

Using this equipment, domestic cooking was found to be a main source of ultrafine aerosols from gas combustion in stoves, from boiling fish, boiling vegetables, and frying hamburgers and eggs. The measured alveolar deposited surface area (ADSA) of the ultrafine particles during the cooking events significantly increased from a baseline of 72.9 μm²/cm³ to a maximum of 890.3 μm²/cm³ measured during fish boiling in water, and up to 4500 μm²/cm³ during frying of meat. The values measured during the tested cooking events are also significantly higher than the maximum outdoor levels measured in other major towns, ranging from 50 to 70 μm²/cm³. This clearly shows that a domestic activity such as cooking can lead to exposures higher than those derived from automobile traffic in a major European town. Also, significantly high values of total deposited area (4.72 × 10⁷ μm²) and dose per lung area (5.90 × 10⁵ μm²/m²) were determined during the preparation of a whole meal composed of two dishes.

It should be noted that although measured parameters such as the alveolar deposited surface area and the dose per lung area are elevated when compared with baseline values, they cannot, at this stage, be ascertained as toxicity indicators. Nevertheless, they point to important contamination by potentially hazardous aerosols released from cooking activities.

Also, it should be noted that if exposure, as determined by this study, is quite high during domestic activities, a prolonged exposure to more intense activities that occur during a work shift in restaurants and other cooking preparation establishments can be quite damaging to health, without taking appropriated individual protection measures, and this shows the need for further studies and investigations.

Data obtained in this study are basic information allowing us to understand the relationship between exposure to ultrafine particles in indoor atmospheres and health effects, which should be the basis for epidemiologic studies.

Further research is needed in order to provide a better understanding of potential exposures in the indoor microenvironment, by measuring also the size distribution of ultrafine particles, number of particles per air volume, and also the chemical composition and information on the shape and crystalline nature of these particles, bearing in mind the development of appropriate exposure of preventive/reductive strategies, as pointed out by Buonanno et al. (2010).