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Exposure to polycyclic aromatic hydrocarbons (PAHs), mutagenic aldehydes and particulate matter during pan frying of beefsteak
  1. Ann Kristin Sjaastad,
  2. Rikke Bramming Jørgensen,
  3. Kristin Svendsen
  1. Department of Industrial Economics and Technology Management, Norwegian University of Science and Technology, Trondheim, Norway
  1. Correspondence to Ann Kristin Sjaastad, Norwegian University of Science and Technology, Department of HSE, Trondheim N-7491, Norway; ann.kristin.sjaastad{at}ntnu.no

Abstract

Objectives Cooking with gas or electric stoves produces fumes, especially during frying, that contain a range of harmful and potentially mutagenic compounds as well as high levels of fine and ultrafine particles. The aim of this study was to see if polycyclic aromatic hydrocarbons (PAHs) and higher mutagenic aldehydes which were collected in the breathing zone of the cook, could be detected in fumes from the frying of beefsteak.

Methods The frying was performed in a model kitchen in conditions similar to those in a Western European restaurant kitchen. The levels of PAHs (16 EPA standard) and higher aldehydes (trans,trans-2,4-decadienal, 2,4-decadienal, trans-trans-2,4-nonadienal, trans-2-decenal, cis-2-decenal, trans-2-undecenal, 2-undecenal) were measured during frying on an electric or gas stove with margarine or soya bean oil as the frying fat. The number concentration of particles <100 nm in size (ultrafine) was also measured, as well as the mass concentration of total particulate matter.

Results Levels of naphthalene were in the range of 0.15–0.27 μg/m3 air. Measured levels of mutagenic aldehydes were between non-detectable and 61.80 μg/m3 air. The exposure level of total aerosol was between 1.6 and 7.2 mg/m3 air. Peak number concentrations of ultrafine particles were in the range of 6.0×104–89.6×104 particles/cm3 air.

Conclusion Naphthalene and mutagenic aldehydes were detected in most of the samples. The levels were variable, and seemed to be dependent on many factors involved in the frying process. However, according to the present results, frying on a gas stove instead of an electric stove causes increased occupational exposure to some of the components in cooking fumes which may cause adverse health effects.

  • Cooking fumes
  • occupational exposure
  • number concentration
  • ultrafine particles
  • trans,trans-2,4-decadienal
  • hygiene/occupational hygiene
  • cancer
  • exposure monitoring
  • indoor air
  • polyaromatic hydrocarbons (PAHs)

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Introduction

Cooking fumes, especially from frying, contain fine and ultrafine particles and several specific agents which may cause adverse health effects in the lung.1–4

Cooking fumes have shown mutagenic activity and may be a risk factor in lung cancer.5 6 Emissions from high-temperature frying have recently been classified as “probably carcinogenic to humans (group 2A)” by the International Agency for Research on Cancer (IARC).7 An increased risk of respiratory tract cancer in cooks and bakers has been reported.8 Among the compounds which have been identified as mutagenic in cooking fumes are polycyclic aromatic hydrocarbons (PAHs), heterocyclic amines and higher aldehydes.9–11

Among the PAHs identified in fumes from the heating of different cooking oils are benzo(a)pyrene (BaP), dibenzo(a,h)anthracene, benzo(a)anthracene (BaA) and benzo(b)fluoranthene. These have been detected in fumes from corn oil, vegetable oil and safflower oil.9 In addition, BaP and BaA have been identified in fumes from soya bean oil, rapeseed oil and lard.12 BaP, dibenzo(a,h)anthracene and BaA are considered probable human carcinogens (group 2A) and benzo(b)fluoranthene is considered a possible human carcinogen (group 2B) by IARC.11

Naphthalene, the most volatile PAH, is classified as a possible human carcinogen (group 2B) by IARC,13 and has been identified in fumes from rapeseed oil (9.4–13 ng/m3), soya bean oil (11–14 ng/m3) and lard (15–16 ng/m3).12

The thermal stressing of cooking oils rich in polyunsaturated fatty acids generates various higher aldehyde species, such as trans-2-alkenals, trans,trans-alka-2,4-dienals and n-alkanals.14

In fumes from peanut oil heated to temperatures of about 100°C, the compounds identified as those with the strongest mutagenicity in the Ames test (in descending order) were: trans,trans-2,4-decadienal (t,t-DDE), trans,trans-2,4-nonadienal, trans-2-decenal and trans-2-undecenal.15 t,t-DDE has also been detected in cooking fumes from heating other oils such as rapeseed oil and soya bean oil, and is considered to be the major mutagenic and cytotoxic compound in oil fumes.16 A ROS-dependent mechanism for t,t-DDE-induced cell proliferation in human bronchial epithelial cells has been suggested.17

Exposure to ultrafine airborne particles (aerodynamic diameter <0.1 μm) has been identified as an important factor affecting human health.18 19 Such exposure is thought to cause oxidative stress in pulmonary cells,20 21 and to enhance allergic reactions and pulmonary inflammation.22 23

The aim of this study was to see if PAHs and higher mutagenic aldehydes could be detected in fumes, which were collected in the breathing zone of the cook, from the frying of beefsteak, and to see if there were differences between levels of PAHs, higher aldehydes and airborne particles when frying on an electric or a gas stove with two different frying fats (margarine and soya bean oil).

Methods

The measurements were performed during the frying of beefsteak following a standardised procedure representative of real-life conditions, that is, conditions similar to those in a Western European restaurant kitchen during the frying of beefsteak.

Materials

Beefsteak, margarine and soya bean oil of two different brands were purchased from a local grocery store. The margarine used contained soya bean oil, rapeseed oil, coconut oil, palm oil and vitamins A and D, and was without hydrogenated fats.

Location

The experiment was performed in a laboratory kitchen especially built for this study. The kitchen was 19 m2 (56.1 m3) and was equipped with a modern kitchen fume extractor (canopy hood) with the exhaust outlet outside the building, an electric stove and a gas stove. The canopy hood was mounted centrally on one of the walls. During the experiments, the stove being used was placed directly under the hood and 65 cm below it. During frying, the hood extracted 335 m3 air/h. Basic ventilation in the kitchen consisted of 119 m3/h air supply and 112 m3/h outlet (without kitchen hood ventilation).

Frying procedure

The beefsteak (400 g) was fried following a standard procedure in a pan with margarine or soya bean oil using a gas or electric stove, as described in detail elsewhere.24

All sampling was conducted continuously during 1 day of frying (214–229 min). The standard frying procedure (15 min) was repeated five times during each day of frying. The repetitions were separated by a 25 min break without ventilating the kitchen. There was also a 25 min break after the last repetition. The aim of this was to make each day of frying last at least 200 min, which was the lower limit for the lab to be able to detect PAHs in the samples.

PAH measurements

The levels of PAHs were measured by use of a glass fibre filter (37 mm) in a closed face filter cassette and two XAD(II) tubes (back-up and sampling tube: Supelco, Bellefonte, Pennsylvannia, USA) connected to a pump (SKC Sidekick; SKC, Eighty Four, PA). The sampling flow rate was 1 l per minute. The sampling was performed as personal measurements, with the glass fibre filter and the tubes placed on the left shoulder of the person frying the beefsteak (the cook).

The analyses were performed by a certified commercial laboratory with Danish accreditation no. 168 for a selection of PAH components (16 EPA standard), following a method of analysis which is a modified version of AMI L5, NIOSH 5515, ISO/CD 12884 and VDI 3873.25

Aldehyde measurements

The levels of higher aldehydes were measured by use of stainless steel tubes (ATD tubes: Markes International Ltd., Pontyclum, UK) with 220 mg Tenax TA (Absorbent Tenax TA 35/60 mesh: Alltech, Deerfield, Illinois, USA) and a pump (SKC Pocket pump) with a sampling flow rate of 100 ml/min. The sampling was performed as personal measurements, with the tubes placed on the left shoulder of the cook.

The analyses were performed by a certified commercial laboratory according to procedures described elsewhere.24

Sampling of total particles

The sampling of total particles was performed using preweighed, double Gelman AE glass fibre filters (37 mm Gelman AE-filter: Gelman Sciences Inc., Ann Arbor, Michigan, USA) placed in a closed face, clear styrene, acrylonitrile cassette connected to a pump (Casella Vortex standard 2: Casella CEL Ltd., Bedford, UK) with an air flow of 2 l/min. The filter cassette was placed on the right shoulder of the cook. Before and after sampling, the filters were conditioned in an exiccator for 24 h and the filters were analysed gravimetrically.

Registration of ultrafine particles

A TSI 3936 Scanning Mobility Particle Sizer (TSI, Shoreview, MN) system was used to measure the total number concentration of ultrafine particles.

The following settings were used for these measurements. The electrostatic classifier was fitted with a 0.0457 cm impactor nozzle with a flow rate of 0.3 l/min and a sheath flow rate of 3.0 l/min. This corresponds to a measurement range of 14.3–673.2 nm. Scanning time was 2 min 15 s. Sampling was started every 3 min and lasted throughout the entire frying period. Measurements were made during 1 day of frying for each of the different combinations of parameters (margarine on the electric stove, soya bean oil on the electric stove, margarine on the gas stove and soya bean oil on the gas stove). The samples were drawn through a flexible silicone tube (TSI conductive silicone tubing (TSI type 3001903) for particle transport). This tube fits the impactor of the electrostatic classifier optimally (1/4 inch). The length of the tube was 2.65 m. The inlet of the silicone tube was placed on the right shoulder of the cook.

Statistical analyses

All analyses were performed using SPSS v 16.0. The comparisons of means were calculated by univariate analyses in a general linear model.

Results

Polycyclic aromatic hydrocarbons

In this study, naphthalene was the only PAH registered in samples from all the different combinations of parameters tested during the frying of beefsteak. The mean levels of PAHs (μg/m3) measured under the different conditions are presented in table 1.

Table 1

Polycyclic aromatic hydrocarbons (μg/m3) and total particles (mg/m3) measured above detection limits in the breathing zone of the cook during the pan frying of beefsteak using an electric stove or a gas stove using margarine or soya bean oil as the frying fat

Levels of naphthalene were registered above the detection limit in 16 of 17 samples. The non-detectable value was substituted by L/21/2, where L is the detection limit.26

Aldehydes

Table 2 describes the quantity of the higher aldehydes measured in the breathing zone of the cook during frying with margarine or soya bean oil on the electric or gas stove.

Table 2

Higher aldehydes (μg/m3) measured in the breathing zone of the cook during the pan frying of beefsteak using an electric stove or a gas stove using margarine or soya bean oil as the frying fat

The group “alkanals” in table 2 consisted of nine different alkanals (butanal, pentanal, hexanal, heptanal, octanal, nonanal, decanal, undecanal and dodecanal), and the group “alkenals” of 2-heptenal, 2-octenal, 2-nonenal, 4-nonenal and trans,trans-2,4-heptadienal, all of which were present in various quantities.

Frying on the gas stove with margarine produced statistically significantly higher levels of t,t-DDE, 2.4-decadienal, c-2-decenal, 2-undecenal and alkanals than frying with margarine on the electric stove. Frying on the gas stove with soya bean oil gave statistically significantly higher levels of t,t-DDE, 2.4-decadienal, t-2-decenal, 2-undecenal, alkanals and alkenals than frying with soya bean oil on the electric stove.

Total particles

The mean mass concentrations of total particles measured in the breathing zone of the cook during a standard frying procedure under the different conditions are given in table 1.

Frying on the gas stove, both with margarine and soya bean oil, gave statistically significantly higher mean mass concentrations of total particles than frying on the electric stove.

Ultrafine particles

The particle size distribution for ultrafine particles at different times after the start of frying with the different combinations of parameters is described in figure 1. Note that the scale on the axis describing particle concentration (dN/dlog (Dp)) is not the same for cooking on a gas stove as for cooking on an electric stove.

Figure 1

Particle size distribution at different times after the start of frying when using a gas stove and soya bean oil as the frying fat (a) or a gas stove and margarine as the frying fat (b) and using an electric stove and soya bean oil as the frying fat (c) or an electric stove and margarine as the frying fat (d).

The peak number concentration of ultrafine particles measured during frying on the electric stove with margarine, on the electric stove with soya bean oil, on the gas stove with margarine and on the gas stove with soya bean oil was 6.0×104, 14.6×104, 89.6×104 and 89.3×104 particles/cm3, respectively.

Discussion

Polycyclic aromatic hydrocarbons

The levels of naphthalene and other PAHs measured in our study were low compared to the occupational exposure limit (OEL) for PAH (total PAH in Norway: 40 μg/m3)

BaP was detected in two of the 17 samples, both collected during frying with margarine on the gas stove. The OEL for BaP in some countries is 2 μg/m3 (Austria, Canada and Sweden)27 and the measured level was less than one tenth of this OEL.

In a Chinese study on air pollution in Chinese kitchens, it was found that naphthalene was the most predominant two-ring PAH.12 This was explained as partly being the result of oil fumes from cooking and indoor smoking, but was mainly attributed to evaporation from mothballs in bedroom wardrobes. However, our detection of naphthalene as the dominant PAH in cooking fumes in a kitchen and building where no mothballs were present may indicate that cooking may also be the main source of naphthalene in the Chinese study.

Aldehydes

Higher aldehydes were detected in all samples, and mutagenic aldehydes in most of the samples. The highest levels of mutagenic aldehydes were measured during frying on the gas stove.

Compared to results from a previous study,24 the aldehyde levels measured during the frying of beefsteak in the present study are high. This may be caused by degradation in the oil over time. Some of the soya bean oil used in the present study had been stored at room temperature in a plastic container for almost a year. Studies have shown that edible oils go through an oxidising process associated with the generation of hydroperoxides and their degradation, and the formation of secondary oxidation products.28 Among the secondary products detected from sunflower oil after oxidation in an oven at 70°C with circulating air for 11 days are t,t-DDE, t-2-decenal, t-2-undecenal and various other aldehydes.29 Some of these compounds were also detected in the headspace of sunflower oil after storage at room temperature for 112 months.30

PAHs and heterocyclic amines have previously been identified as the main mutagenic compounds in cooking fumes.1 10 However, a study on the mechanisms behind the association between exposure to cooking oil fumes (COF) and lung cancer indicates that COF induces anti-apoptotic effects, contributing to the cell survival and proliferation of A-549 lung cancer cells and that t,t-DDE from COF may make a more important contribution than PAHs (BaP) to this mechanism.31

Total particles

The mass concentration of total particles in the breathing zone of the cook was measured so that personal exposure during frying in the laboratory kitchen could be compared with the cooking fume exposure of professional cooks as measured in previous studies.

In a study conducted on professional cooks in restaurants in Norway, personal exposure levels were in the range 0.08–2.95 mg/m3.2 These measurements were made over 1.5–2.5 h during a work shift, with varying amounts of time spent frying meat and the use of various kinds of frying fats. During a working day in a restaurant kitchen, earlier studies have indicated that the mean time frying spent is 59% of the working hours for women and 56% for men.4 The time weighted average for these components of COF in the present study will thus be between 50% and 60% of the measured values, which gives good agreement with the previous study.

Ultrafine particles

The peak number concentrations registered during frying on the gas stove are considerably higher than during frying on the electric stove.

During frying on the gas stove, the peak number concentration consists of the smaller particles (Dp=40–60 nm) in the ultrafine size fraction, whereas the peak number concentration during frying on an electric stove consists of particles 80–100 nm in size.

Our study shows that using a gas stove instead of an electric stove results in higher levels of PAHs, aldehydes and particles. This is presumed to be due to the higher temperature of the gas flame resulting in more thermal degradation products. The higher level of ultrafine particles may also be due to the gas flame itself and not just a result of the cooking process.

Conclusions

The measured levels (time weighted average) of total particles and PAHs for the cooks in our study are far below the Norwegian OELs for nuisance dust (10 mg/m3) and total PAH (40 μg/m3). However, cooking fumes consist of a mixture of toxic and mutagenic compounds, including mutagenic aldehydes and heterocyclic amines with no known dose–response relationship, so exposure to cooking fumes should be reduced as much as possible.

What this paper adds

  • Occupational exposure to cooking fumes may cause adverse health effects.

  • Cooking fumes are known to contain mutagenic and carcinogenic compounds, but exposure levels during frying with different types of heating sources or different frying fats have not been studied.

  • Mutagenic compounds, such as polycyclic aromatic hydrocarbons (PAHs) and higher aldehydes are present in the breathing zone of the cook during the frying of beefsteak under real-life conditions.

  • Compared to frying on an electric stove, frying on a gas stove may cause increased occupational exposure to some of the hazardous components in cooking fumes.

  • Exposure to cooking fumes should be reduced as much as possible.

References

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Footnotes

  • Funding This study has been financed with the aid of EXTRA funds from the Norwegian Foundation for Health and Rehabilitation. The funding source had no involvement in the study design; in the collection, analysis, and interpretation of data; in the writing of the report; and in the decision to submit the paper for publication.

  • Competing interests None.

  • Provenance and peer review Not commissioned; externally peer reviewed.