Midget Impinger Research Articles

Evaluation of methylene diphenyl diisocyanate as an indoor air pollutant and biological assessment of methylene dianiline in the polyurethane factories

Today many raw materials used in factories may have a dangerous effect on the physiological system of workers. One of them, which is widely used in the polyurethane factories, is diisocyanates. These compounds are widely used in surface coatings, polyurethane foams, adhesives, resins, elastomers, binders, and sealants. Exposure to diisocyanates causes irritation to the skin, mucous membranes, eyes, and respiratory tract. Methylene dianiline (MDA) is a metabolite of methylene diphenyle diisocyanate (MDI), an excretory material of worker's urine who are exposed to MDI. Around 100 air samples were collected among five factories by the Midget Impinger, which contained DMSO absorbent as a solvent and Tryptamine as a reagent. Samples were analyzed by high-performance liquid chromatography with an EC\\UV detector using the NIOSH 5522 method of sampling and analysis. Also, fifty urine samples were collected from workers by using William's biological analysis method. The concentration of MDI in all air samples was more than 88 μg/m3, showing a high concentration of the pollutant in the workplaces in comparison with the NIOSH standard, and all the worker's urine was contaminated by MDA. The correlation and regression tests were used to obtain statistical model for MDI and MDA that is useful for prediction of diisocyanates pollution situation in the polyurethane factories.

Evaluation of a Methodology for Quantifying the Effect of Room Air Ultraviolet Germicidal Irradiation on Airborne Bacteria

As a result of the recent resurgence in tuberculosis (TB) and the increasing incidence of multidrug-resistant TB, there has been renewed interest in engineering controls to reduce the spread of TB and other airborne infectious diseases in high-risk settings. Techniques such as the use of lamps that produce ultraviolet germicidal radiation may reduce exposure to infectious agents by inactivating or killing microorganisms while they are airborne. We designed and evaluated a test method to quantitatively estimate the efficacy of germicidal lamps, in conjunction with dilution ventilation, for reducing the concentration of viable airborne bacteria. Bacterial particles were generated in a 36m3 room and collected with midget impingers at 5-7 locations. The effectiveness of the control technique was determined by comparing concentrations of culturable airborne bacteria with and without the control in operation. Results for a single, 15 W germicidal lamp showed reductions of 50% for Bacillus subtilis (B. subtilis) and Micrococcus luteus (M. luteus); tests with Escherichia coli (E. coli) showed nearly 100% reduction (E. coli were isolated only from the sampler nearest the aerosol source when the lamp was operating). The addition of louvers to a lamp greatly reduced its efficacy. Decay experiments showed that roughly 4-6 equivalent air changes per hour were achieved for B. subtilis with one or two lamps operating. These preliminary experiments demonstrated that this methodology was well suited for these evaluations and identified factors that could be modified to refine the study design for future work.

Airborne thermal degradation products of polyurethene coatings in car repair shops.

A methodology for workplace air monitoring of aromatic and aliphatic, mono- and polyisocyanates by derivatisation with di-n-butylamine (DBA) is presented. Air sampling was performed using midget impinger flasks containing 10 ml of 0.01 mol l(-1) DBA in toluene and a glass-fibre filter in series after the impinger flask, thereby providing the possibility of collecting and derivatising isocyanates in both the gas and particle phases. Quantification was made by LC-MS, monitoring the molecular ions [MH]+. Air samples taken with this method in car repair shops showed that many different isocyanates are formed during thermal decomposition of polyurethane (PUR) coatings. In addition to isocyanates such as hexamethylene (HDI), isophorone (IPDI), toluene (TDI) and methylenediphenyl diisocyanate (MDI), monoisocyanates such as methyl (MIC), ethyl (EIC), propyl (PIC), butyl (BIC) and phenyl isocyanate (PhI) were found. In many air samples the aliphatic monoisocyanates dominated. During cutting and welding operations, the highest levels of isocyanates were observed. In a single air sample from a welding operation in a car repair shop, the highest concentrations found were: MIC, 290; EIC, 60; PIC, 20; BIC, 9; PhI, 27; HDI, 105; IPDI, 39; MDI, 4; and 2,4-TDI and 2,6-TDI 140 microg m(-3). Monitoring the particle size distribution and concentration during grinding, welding and cutting operations showed that ultrafine particles (< 0.1 microm) were formed at high concentrations. Isocyanates with low volatility were mainly found in the particle phase, but isocyanates with a relatively high volatility such as TDI, were found in both the particle and gas phases.

Collection Efficiency for Submicron Particles of a Commonly Used Impinger

The collection efficiency for submicron particles of an all-glass impinger, under conditions commonly used by industrial hygienists, was studied by measuring the removal of particles from a polydisperse polystyrene aerosol. Collection efficiencies for water and dimethylformamide as sampling liquids at flow rates of 0.7, 1.0, and 2.0 L/min were determined. The collection efficiency at a flow rate of 1.0 L/min was found to be less than 20% for particles with a diameter between 0.02 and 0.7 µm. When thermally generated particles are a part of the exposure pattern and air measurements are made using the all-glass midget impinger as the collection device, the particulate contribution to the exposure could be severely underestimated due to poor collection efficiency in the submicron range.

A Combined Fluorochrome Method for Quantitation of Metabolically Active and Inactive Airborne Bacteria

To better understand the ecology of microorganisms in the environment and to quantify the concentrations of airborne microorganisms, methods are needed to count all microbial cells that are present and differentiate between those that are metabolically competent and those that are nonviable as they exist in situ. We developed and tested a direct epifluorescent method to estimate the quantity and activity of airborne bacteria aerosolized into full-scale rooms. Midget impingers, filled with the fluorescing redox dye 5-cyano-2, 3-ditolyl tetrazolium chloride (CTC), were used to capture and stain metabolically active bacteria from room air. Both active and inactive bacteria were counterstained with a fluorescein derivative and counted with an epifluorescent microscope. The choice of fluorochrome stains allowed concurrent identification of active and inactive bacteria in the same microscopic field. Airborne bacterial numbers determined by epifluorescence microscopy were compared to standard, nonselective colon...

Particle Generation Method for Toxic Substances and Collection Efficiency of o-Tolidine Particles by Midget Impinger

Particle Generation Method for Toxic Substances and Collection Efficiency of o-Tolidine Particles by Midget Impinger

Determination of complex mixtures of airborne isocyanates and aminesPart 4.† Determination of aliphatic isocyanates as dibutylamine derivatives using liquid chromatography and mass spectrometry

An LC–MS method is presented for the determination of aliphatic isocyanate [hexamethylene diisocyanate] (HDI), isophorone diisocyanate (IPDI), biuret and isocyanurate] adducts of HDI as their dibutylamine (DBA) derivatives. The method is based on sampling in midget impinger flasks containing 10 ml of 0.01 mol l–1 DBA in toluene (see parts 1–3 of this series†). The excess reagent and the solvent are removed by evaporation. The enriched samples are then analysed using LC–electrospray MS. Quantification of HDI–DBA and IPDI–DBA was effected by monitoring the molecular ion [MH]+. Linear calibration graphs were obtained in the range 50–500 nmol l–1 with correlation coefficients of 0.9965–0.9997. The RSD for samples spiked at a concentration of 1 nmol l–1 was 1.7 and 2.9% for the two IPDI–DBA isomers (n = 8) and 1.2% for HDI–DBA (n = 8). On injecting 4 µl of the 0.5 ml sample, the instrumental detection limit was about 20 nmol l–1, which corresponds to about 0.1 µg m–3 for HDI and 0.2 µg m–3 for IPDI for a 15 l air sample.No degradation was observed after storage of the derivatives for up to 4 months in acetonitrile or toluene. No losses were seen when the derivatization reaction took place in the presence of interferents such as morpholine, hexamethylenediamine, isophoronediamine and phenol corresponding to concentrations of 10 ppm in air for a 15 l air sample. The influence of water was studied by spiking with volumes corresponding to a relative humidity of 80% at 30 °C in 15 l of air. The reaction rates of HDI and IPDI with DBA were found to be 2–3 times faster than those for 1-(2-methoxyphenyl)piperazine.

Determination of complex mixtures of airborne isocyanates and amines. Part 5. Determination of low molecular weight aliphatic isocyanates as dibutylamine derivatives.

A method is presented for the determination of low molecular weight aliphatic isocyanates, methyl isocyanate (MIC), ethyl isocyanate (EIC), propyl isocyanate (PIC) and butyl isocyanate (BIC), as their dibutylamine (DBA) derivatives. The method is based on sampling in midget impinger flasks containing 10 ml of 0.01 mol l-1 DBA in toluene (as in Parts 1-4 in this series). The samples are analysed using liquid chromatography-electrospray mass spectrometry (LC-ESP-MS) or gas chromatography-mass spectrometry using chemical ionisation with ammonia, monitoring positive ions (GC-PCI). Quantification was effected by monitoring the molecular ions MH+. Aliquots of 10 ml of toluene solutions containing 0.01 mol l-1 DBA were spiked with 0.03-0.85 microgram of MIC-, EIC-, PIC- and BIC-DBA. The correlation coefficients for LC-ESP-MS were in the range 0.9952-0.9999 (n = 14). The repeatability (RSD) was in the range 0.37-1.2% (0.12-0.34 microgram ml-1, n = 10). The instrumental detection limit for MIC was about 15 micrograms l-1, which corresponds to about 0.5 microgram m-3 in a 15 l air sample. The correlation coefficients for GC-PCI were in the range 0.9913-0.9990. The repeatability (RSD) was in the range 1.1-4.9% (0.12-0.34 microgram ml-1, n = 10). The instrumental detection limit for MIC was about 0.2 microgram l-1, which corresponds to about 0.05 microgram m-3 in a 15 l air sample. Using electron ionisation, the instrumental detection limit for MIC was about 10 micrograms l-1. No derivatisation reaction losses were seen when the derivatization reaction between PIC and DBA took place in the presence of morpholine, propylamine, ethanol, phenol and water. When mineral wool with a phenol-formaldehyde-urea resin was thermally degraded, 0.1% m/m of MIC was released. In air samples taken on top of a new electric oven insulated with mineral wool, MIC was found in the range 0.1-3 mg m-3. No MIC in air was found from a pre-heated oven.

Air and biological monitoring of toluene diisocyanate in a flexible foam plant.

Comparative air measurements of toluene diisocyanate (TDI) were performed in a 5.6 m3 standard atmosphere and at a TDI flexible foam plant. Air samples were collected in midget impinger flasks containing 9-(N-methyl-amino-methyl)-anthracene (MAMA) in toluene and on 13-mm glass-fiber filters impregnated with MAMA and glycerol analyzed by LC-UV and with filter-tape instruments. In the laboratory study the average amounts of the TDI-MAMA derivatives determined were higher for filters compared to impingers when tested at concentrations between 16 and 150 micrograms/m3 (n = 29). At the TDI foaming plant the amount of TDI-MAMA collected on the filters compared with impingers showed higher TDI values at low concentrations and lower values at higher concentrations. The same was seen for the filter-tape measurements, but for two samples at very low concentrations the response was much lower. The average air concentration was 29.8 micrograms/m3 (12.5-79.9; n = 12). The highest exposure peak measured was approximately 3 mg TDI/m3. 2,4- and 2,6-toluene diamine (TDA) in urine (U-TDA) and in plasma (P-TDA) from four exposed workers and one volunteer were determined after strong acid hydrolysis as their pentafluoro-propionic anhydride derivatives using gas chromatography-mass spectrometry. The ions monitored were the M-20 ions (M = molecular weight) of the TDA and trideuterium labeled TDA as the internal standard. The P-TDA among the workers varied between 1-38 micrograms/L and between 7-24 micrograms/L for 2,4- and 2,6-TDA, respectively. The individual plasma levels among the workers over the 3-day periods varied between 7-73%. For the volunteer, P-TDA reached a maximum about 24 hours after the last exposure. The half-time of P-TDA for the volunteer was about 10 days. The urine levels (U-TDA) varied greatly with time and exposure. High peaks were found during or shortly after the exposure. No clear correlation between air levels of TDI measured with the filter-tape instruments and levels of TDA in hydrolyzed urine and plasma was seen, but the U-TDAMax followed the exposure in time as measured with the filter-tape instruments.

Air and Biological Monitoring of Toluene Diisocyanate in a Flexible Foam Plant

Comparative air measurements of toluene diisocyanate (TDI) were performed in a 5.6 m3 standard atmosphere and at a TDI flexible foam plant. Air samples were collected in midget impinger flasks containing 9-(N-methyl-amino-methyl)-anthracene (MAMA) in toluene and on 13-mm glass-fiber filters impregnated with MAMA and glycerol analyzed by LC-UV and with filter-tape instruments. In the laboratory study the average amounts of the TDI-MAMA derivatives determined were higher for filters compared to impingers when tested at concentrations between 16 and 150 μg/m3 (n=29). At the TDI foaming plant the amount of TDI-MAMA collected on the filters compared with impingers showed higher TDI values at low concentrations and lower values at higher concentrations. The same was seen for the filter-tape measurements, but for two samples at very low concentrations the response was much lower. The average air concentration was 29.8 μg/m3 (12.5−79.9; n=12). The highest exposure peak measured was approximately 3 mg TDI/m3.2,4- and 2,6-toluene diamine (TDA) in urine (U-TDA) and in plasma (P-TDA) from four exposed workers and one volunteer were determined after strong acid hydrolysis as their pentafluoro-propionic anhydride derivatives using gas chromatography-mass spectrometry. The ions monitored were the M-20 ions (M=molecular weight) of the TDA and trideuterium labeled TDA as the internal standard. The P-TDA among the workers varied between 1–38 μg/L and between 7–24 μg/L for 2,4- and 2,6-TDA, respectively. The individual plasma levels among the workers over the 3-day periods varied between 7–73%. For the volunteer, P-TDA reached a maximum about 24 hours after the last exposure. The half-time of P-TDA for the volunteer was about 10 days. The urine levels (U-TDA) varied greatly with time and exposure. High peaks were found during or shortly after the exposure. No clear correlation between air levels of TDI measured with the filter-tape instruments and levels of TDA in hydrolyzed urine and plasma was seen, but the U-TDAMax followed the exposure in time as measured with the filter-tape instruments.

Comparison Between Solid Sampler and Impinger for Evaluation of Occupational Exposure to 1,6-Hexamethylene Diisocyanate Polyisocyanates During Spray Painting

This study evaluated two air sampling methods for monitoring the level and the variability of a painter's exposure to HDI polyisocyanates while spraying Tolonate-based paints in typical autobody repair shop paint booths. Personal air samples were collected by midget impingers containing 1-(2-methoxyphenyl)piperazine (MPP) absorber solution and MPP-impregnated filters. HDI biuret and isocyanurate, the principal polyisocyanates in Tolonate paint systems, were analyzed concurrently by two different laboratories. Potential exposure to HDI polyisocyanates measured by impinger devices ranged from 0.25 to 3 mg/m3. Impregnated filters significantly underestimated atmospheric concentrations of HDI polyisocyanates in the painter's breathing zone. The use of an appropriate half-face mask with 90% efficiency was recommended, since it reduced the residual exposure well below the STEL (1 mg/m3) now proposed in a few countries and recommended by manufacturers of polyisocyanates.

Determination of complex mixtures of airborne isocyanates and amines. Part 2. Toluene diisocyanate and aminoisocyanate and toluenediamine after thermal degradation of a toluene diisocyanate–polyurethane

An LC–MS method is presented for the determination of thermal decomposition products of polyurethane. The method is based on the collection of air samples in midget impinger flasks containing 0.01 mol l–1 dibutylamine (DBA) dissolved in toluene. DBA reacts with isocyanates to give urea derivatives. The amines simultaneously collected were derivatized with ethyl chloroformate (ET) to give urethane derivatives. Two isomers of toluene diisocyanate (2,4-and 2,6-TDI), toluene-2,4-and-2,6-diamine (TDA), three isomers of toluene aminoisocyanates and oligomers with two and three aromatic rings were determined in air containing thermal decomposition products of TDI–polyurethane. LC with gradient elution, at 0.5 ml min–1 starting with acetonitrile–water (46 + 54) and ending after 14 min with acetonitrile–water (77.5 + 22.5) and atmospheric pressure ionization monitoring of positive ions demonstrated highly sensitive and selective determinations. Quantification was performed by monitoring the molecular ion [M + 1]+ of TDI–DBA and TDA–ET derivatives. The instrumental detection limit was 1 nmol l–1 of TDI–DBA and 2 nmol l–1 of TDA–ET. Linear calibration curves were obtained and the correlation coefficient was 0.9981–0.9996 for 50–500 nmol l–1(n= 14). The over-all precision for samples spiked at a concentration of 500 nmol l–1 of 2,4-and 2,6-TDA–ET and 2,4-and 2,6-TDI–DBA was 1.7, 1.6, 1.8 and 1.9%(n= 11), respectively.

Formaldehyde Exposure in the Funeral Industry

Abstract An assessment of formaldehyde exposure was conducted among embalmers in the funeral industry in the province of Manitoba, Canada. The occupational exposure limit is defined by the American Conference of Governmental Industrial Hygienists' threshold limit value-ceiling of 0.37 mg/m3 (0.3 ppm). Personal and area midget impingers were used to monitor the embalming procedure. Samples were analyzed according to the National Institute for Occupational Safety and Health Method 3500. Thirty-six embalmings were monitored in 18 chapels. Personal formaldehyde exposures of embalmers during an intact body preparation (< 1 hour) ranged from 0.12 to 5.64 mg/m3 [arithmetic mean (AM) = 0.78, standard deviation (SD) = 1.06, number (N) = 24]. During an autopsy preparation (<2 hours >), exposures ranged from 0.11 to 4.13 mg/m3 (AM = 0.80, SD = 0.96, N = 24). Student's t-test did not present a significant difference (p > 0.05) between the two types of body preparations. Concentration for area samples ranged from 0.05 to 8.37 mg/m3 (AM = 0.61, SD = 1.24, N = 72). Health effects identified by some embalmers included irritation of the mucous membranes and chest tightness. Most embalmers are immunized with the hepatitis B vaccine. Universal precautions against infectious agents were not strictly adhered to in most embalmings. An upgrading of engineering controls, improved work practices, and use of personal protective equipment was required in the majority of funeral chapels. The principle of down-draft ventilation was adapted to some existing morgue tables. Compliance under the Canadian Workplace Hazardous Materials Information System Legislation was reviewed. In conclusion, the majority of embalmers operating funeral chapels in Manitoba were being overexposed to airborne formaldehyde according to the standard.

A survey of airborne HDI, HDI-based polyisocyanate and solvent concentrations in the manufacture and application of polyurethane coatings.

This study summarizes the results of industrial hygiene surveys performed between 1979 and 1987 in paint manufacturing and application operations using polyurethane coatings containing hexamethylene diisocyanate (HDI) and HDI-based polyisocyanates (trade name Desmodur N). A total of 466 Desmodur N and 457 HDI samples were collected from 47 operations most of which were in application. The application surveys covered manufacture and refinishing of transportation vehicles, painting of large military and civilian equipment, industrial finishing operations, and maintenance and construction operations. The primary objective of the surveys was to assess the potential exposure to HDI and HDI-based polyisocyanate. In more than 60% of the surveys, concentrations of airborne organic solvents also were monitored. Isocyanates were sampled using toluene/nitroreagent in midget impingers, and solvents were collected using charcoal tubes. They were analyzed using high pressure liquid chromatography and gas chromatography, respectively. The data from these workplace situations show there is some potential for isocyanate overexposure of unprotected workers and that it is greater in spray than in nonspray operations.

Sampling efficiencies of all-glass midget impingers

Midget impingers are used to sample mists, sprays and bioaerosols for occupational hygiene measurements. This report describes measurements of the sampling efficiency of two midget impingers for airborne liquid droplets in the size range 2–40 μm in calm air. Although impingers were found to be at least 70% efficient in collecting droplets larger than 5 μm, there was a fall in efficiency for smaller droplets.

Aerosols Created by Some Surgical Power Tools: Particle Size Distribution and Qualitative Hemoglobin Content

Abstract Prompted by concerns about exposure to blood and other body substances, the possible generation of blood-containing aerosols in orthopaedic surgical practice was investigated. Common surgical power tools were operated in the laboratory to simulate the aerosols typically generated in common orthopaedic procedures. A bone saw, a Hall drill, a Shea drill, and an electrocautery were used on bone or tendon while blood was slowly dripped over the operative surface. Particle size distribution was evaluated with a low-pressure cascade impactor, and the presence of hemoglobin in inspirable particles was evaluated with the aid of a midget impinger. Particle size distribution depended on the type of power tool used, but most of the particles collected were in the respirable range. Hemoglobin was detected in all samples. Personal sampling is indicated to determine whether inspirable blood aerosols are present in the surgeon's breathing zone during an operation.

Analysis of 1,3-butadiene and other selected gas-phase components in cigarette mainstream and sidestream smoke by gas chromatography-mass selective detection

An analytical procedure was developed for the analysis of 1,3-butadiene, acrolein, isoprene, benzene and toluene in the gas phase of cigarette smoke and environmental tobacco smoke (ETS) utilizing cryogenic gas chromatography-mass selective detection (GC-MSD). The MSD was operated in the selective ion monitoring (SIM) mode. The compounds of interest eluted in less than 15 min. The gas phase of freshly generated mainstream smoke was introduced into the GC-MSD via a 10-port gas sampling valve on a puff-by-puff basis. This method minimizes the ageing of tobacco smoke. The levels of 1,3-butadiene in the mainstream smoke ranged from 16 to 75 micrograms/cigarette. The gas phase of sidestream smoke was trapped in methanol using three midget impingers at -78 degrees C. The amount of 1,3-butadiene in the sidestream smoke ranged from 205-361 micrograms/cigarette. The concentration of 1,3-butadiene in ETS in a smoke-filled bar amounted to 2.7-4.5 micrograms/m3.

The Efficiency of Air Pollutant Sampling by Midget Impingers with Amines as Model Compounds

A theory is developed for air sampling with impingers which expresses the collection efficiency as a function of the equilibrium partition coefficients involved and of the kinetics of the mass transfer from the gas phase to the absorbing solution. The theory also gives a value of the error which arises from an estimation of the sampling efficiency by the common procedure of connecting two impingers in series rather than measuring the difference in pollutant concentration in the inlet and outlet of the sampling device. The difference between theory and experimental results obtained previously by other authors can be explained reasonably with the theory developed here. The theory has been evaluated with amines of different chain lengths and basicity as model substances and with acidic aqueous solutions and toluene as absorbing solutions. When sampling short-chained amines in acidic aqueous solutions, where the amines are protonated immediately, the efficiency is limited by the rate of mass transfer. The efficiency thus varies with flow rate but is independent of sampling volume and also, essentially, of acid concentration. For long-chained amines, which are less soluble in water, sampling should be performed in organic solvents, which leads to fast kinetics. In this case, however, the sampling is based on a reversible equilibrium and the sampling efficiency will depend mainly on the magnitude of the partition coefficient and on the sampling volume. In practice, under typical sampling conditions, at least 95% sampling efficiency can be obtained for all amines studied.

The Efficiency of Air Pollutant Sampling by Midget Impingers with Amines as Model Compounds

A theory is developed for air sampling with impingers which expresses the collection efficiency as a function of the equilibrium partition coefficients involved and of the kinetics of the mass transfer from the gas phase to the absorbing solution. The theory also gives a value of the error which arises from an estimation of the sampling efficiency by the common procedure of connecting two impingers in series rather than measuring the difference in pollutant concentration in the inlet and outlet of the sampling device. The difference between theory and experimental results obtained previously by other authors can be explained reasonably with the theory developed here. The theory has been evaluated with amines of different chain lengths and basicity as model substances and with acidic aqueous solutions and toluene as absorbing solutions. When sampling short-chained amines in acidic aqueous solutions, where the amines are protonated immediately, the efficiency is limited by the rate of mass transfer. The eff...

Determination of benzene, toluene and 1,3-butadiene in cigarette smoke by GC-MSD

An analytical procedure was devised for the determination of selected gas phase constituents in cigarette smoke utilizing capillary gas chromatography and mass selective detection (GC-MSD); the MSD was used in the selective ion monitoring mode (SIM). The gas of freshly generated mainstream smoke was analyzed via a 10-port gas sampling valve on a puff-by-puff basis. Benzene, toluene, and 1,3-butadiene were found in the range of 6–73, 5–88, and 16–75 μg/cigarette, respectively. The gas phase of sidestream smoke was trapped in methanol using 3 midget impingers at −78°C. Benzene in sidestream smoke was found in the range of 490–840 μg/cigarette; toluene and 1,3-butadiene levels were 1,090–1,690 and 300–470 μg/ cigarette, respectively. Environmental tobacco smoke (ETS), sampled in a smoke-filled bar, was analyzed using the cold trap method. The concentrations of benzene and toluene in this indoor air were found to be 26–36 and 41–80 μg/m 3, respectively, while 1,3-butadiene was present at 3.3–4.5 μg/m 3.