NIOSH method 2549: volatile organic compounds (modified).
Since the 70s, research has found in Europe and in the United States that individuals spend between 70 and 90% of their time indoors. Health studies have found that exposures to a variety of air pollutants indoors can be substantially higher than outdoors, even in urban environment. Volatile Organic Compounds (VOCs) are often considered among the more important indoor pollutants, because of by their continue emission from many sources and their diffusion properties. With the aim to evaluate the occupants’ discomfort and health effects and in order to develop guidelines and standards, Indoor Air Quality (IAQ) assessment and control is an essential step. IAQ assessment will complain:
Sources: Identification and characterization of sources, as emissions from materials, products or activities, is best done under laboratory conditions; so it is possible measuring rates of emissions (especially chemicals such as VOCs). Exposure characterization is the second level of source identification; after the measurement of contaminants’ concentrations in controlled environment, characterised by known sources, adsorbing and absorbing surfaces, these data can be used in validation of current exposure models.
Sampling methods: In order to determine concentrations of VOCs and exposures of building occupants via inhalation, field studies can be carried out by sampling methods (and analysis) in accordance with existing official methods (EC, NIOSH, OSHA, ACGIH, etc.). This way may be expensive and cumbersome; in addition, it can be not exhaustive in predicting the discomfort and health impact. A greater number of perspectives are offered by using some “descriptors” that can be more adequate in characterizing anthropogenic pollution. Specific sampling methods may be reserved for contaminants with specific toxic effects (e.g., formaldehyde, benzene, monomers, etc.). Measurements of specific contaminants’ can be necessary for sources that cause high room concentrations for relatively short periods (e.g., in case of freshly applied coatings on walls, etc.). Currently, diffusion (passive) samplers are mainly used in order to evaluate long term exposures (days to weeks and more)
Analysis and data meaning: existing analytical methods are validated and generally show adequate limits of detection (LODs) and limits of quantification (LOQs) even in measuring subtoxic contaminants’ concentrations. Analytical methods for the more frequent indoor contaminants are presented and commented. More difficulties lie in the interpretation of results, due to the limited indications suggested by European and International Standards (such as EN, EN ISO, etc.) that will be discussed. The difficulty in data evaluation is growing depending on the simultaneous occurrence of contaminants at subtoxic concentration.
In this chapter, there will be presented the way to handle the problem in IAQ assessment, and some practical applications, in order to provide the logical pathway to face the majority of actual cases.
2. Indoor air quality and VOCs
Research on pollutant sources is needed to identify pollutants and emission levels from building materials and other products. Work in this area will serve two purposes: (1) providing measurement protocols and data to employ in exposure reduction actions, and (2) providing correlations between research on health effects and pollutant sources of contaminant critical levels. Finally, research is required to determine definition, causes of, and solutions to multiple chemical sensitivity (MCS). Identifying the physiologic nature of MCS is the first step in understanding whether and how IAQ eventually contributes to the syndrome. Maroni et al. (1995) recommended the following definitions that should be used in the description of indoor related complaints and illnesses:
Building-Related Environmental Complaints (BREC): Complaints of poor IAQ or poor indoor air environment. BREC are usually registered in the complaint (annoyance) part of questionnaire studies.
Building-Related Symptoms (BRS) or Building Related Health Complaints (BRC): The health complaints (subjective symptoms) reported by the single individual as occurring inside a building and usually subsiding shortly after leaving it.
Sick Building Syndrome (SBS): denotes a situation where a significant number of the occupants of a building complain of a typical group of general, unspecific, and irritating symptoms, including particularly headache, lethargy, dry eyes, blocked nose, and sore throat. The symptoms usually fade after the person has left the indoor environment but the specific cause is unidentified.
Building-Related Illness (BRI): clinical condition with defined symptoms and signs in which the cause (aetiology) is building-related and identifiable.
The difference between BRI and SBS is that the building problems are identified in the former and undiagnosed in the latter. The term "sick building" probably should not be used on its own, but it might be replaced with the expression "building with indoor climate problems" or "problem building."
VOCs are often more important in assessing IAQ because of their ubiquity; VOCs may be used like “descriptors” that can be more adequate in characterizing anthropogenic pollution. Specific sampling methods may be reserved for contaminants with specific toxic effects (e.g., formaldehyde, benzene, monomers, etc.). In many cases, investigations of the indoor air are carried out because of complaints about poor IAQ, which are made by persons living or working indoors. Such complaints may be perception of unknown or unpleasant odours, headache, irritation of the eyes, nose and throat, dryness of the skin or symptoms like tiredness, lack of concentration and unspecific hypersensitivity reactions. Investigations resulting from observed or suspected health problems of occupants are quite similar and require the same sampling strategy.
Identification of indoor pollutant sources may be very important; emission from point (or surface) sources generates a pronounced concentration gradient near the source. The existence of such concentration gradients can be used to trace the source in an indoor environment by a careful selection of sampling sites. This strategy can lead to recommendations on how to improve indoor air quality, e.g. removing identified materials and strong emitters.
Maroni et al (1995) proposed these recommendations concerning source control:
Manufacturers should be required to provide sufficient information for the evaluation of their products’ safety. Protection of legitimate confidentiality must not impede evaluation.
Standardization and harmonization of emission testing procedures must continue at international level. Meanwhile, research and application of different techniques and methodological intercomparison should be encouraged.
Labelling of products and their ranking for safety and emission properties should be encouraged to facilitate appropriate selection and use by consumers. The choice of process may vary according to the nature of the risk involved and the local priorities.
The growth of moulds and other microorganisms in the indoor environment should be avoided. This can be achieved effectively by elimination of moisture.
Good housekeeping and sanitation rather than the use of biocides are appropriate control measures also for mites.
Overall exposure to VOCs should be kept at the lowest possible level primarily by proper control of the emission sources.
Pending improved methods, the total volatile organic compounds concept is a useful tool for practical assessment of the overall quality of materials and of indoor air. However, at least the type of major VOC species must be known.
More research is recommended for the sensory effects of VOC mixtures and for some individual compounds typically present in indoor air mixtures for which little toxicological knowledge is available; this recommendation is strongly current, due to the growing interest in persistent organic pollutants (POPs) as endocrine disruptors, also in classic subtoxic concentrations.
4. Sampling methods
The primary objective of taking indoor air is to determine the quality of indoor air with the aim of assessing any risk to the health of the population and of individuals due to indoor air pollution. Monitoring is useful also in testing effectiveness of remedial actions, such as modifications to a building, its systems or equipment, aimed at reducing indoor air pollution. The measurements for testing their effectiveness are comparison measurements before and after the remedial actions. It is also important to record intermediate and long-term trends of indoor air pollution concentration. Respective analysis of trends will help to maintain, improve and establish abatement or risk management procedures. Finally, beside screening measurements, it can be very helpful to evaluate indoor air concentrations at abnormal or "worst-case" conditions of the indoor climate (temperature, humidity, ventilation etc.) and during particular activities. Sampling and analytical methods may be also used in validation of indoor pollution models.
To determine reference values of indoor air pollutants, the following elements of sampling strategy shall be used in addition to the basic information characterising every sampling method (EN 14412, 2004):
Time of sampling: to rule out any seasonal effects the individual sampling events shall be evenly distributed over the year. The time of individual sampling shall be fixed in a way that representative concentration values can be assessed. However, for sampling for ≥ one week, the choice of sampling time tends to be less important.
Sampling duration and sampling frequency: the duration of sampling has to be set in a way that the limits of determination for all compounds of interest are exceeded and that representative readings are obtained. It is necessary to maintain a sampling duration of one week or a multiple to achieve a maximum of representativity per sampling site. This is to assess all different pollution loads that occur on the different days of the week at least once. One sampling per site is adequate.
Sampling site and determinations with resolution in space. The sampling site shall be representative, e.g. the centre of the room most inhabited by all occupants shall be used.
General methods (like NIOSH, OSHA or similar) developed for industrial workplaces may be adapted for VOC determination in air; as an example, we report the synthesis of NIOSH Method 2549 (Table 1).
Helium, high purity
Organic compounds of interest for mass spectra verification (See Table 2).*
Solvents for preparing spiking solutions: carbon disulfide (low benzene chromatographic grade), methanol, etc. (99+% purity)
* See SPECIAL PRECAUTIONS
|SAMPLER:||THERMAL DESORPTION TUBE|
(multi-bed sorbent tubes containing graphitized carbons and carbon molecular sieve sorbents [See Appendix])
|FLOW RATE:||0.01 to 0.05 L/min|
|SHIPMENT:||Ambient in storage containers|
|SAMPLE STABILITY:||Compound dependent (store @ -10 °C)|
|BLANKS:||1 to 3 per set|
|ANALYTE:||See Table 1|
|INJECTION VOLUME:||Defined by desorption split flows (See Appendix)|
|TEMPERATURE||-DESORPTION:||300 °C for 10 min|
|-DETECTOR (MS):||280 °C|
|-COLUMN:||35 °C for 4 min; 8 °C/min to 150 °C,|
15 °C/min to 300 °C
|COLUMN:||30 meter DB-1, 0.25-mm ID,|
1.0-μm film (or equivalent)
|CALIBRATION:||Identification based on mass spectra|
interpretation and computerized library searches.
|ESTIMATED LOD:||100 ng per tube or less|
|PRECISION (Sr):||not applicable|
Sampler: Thermal sampling tube, ¼” s.s. tube, multi-bed sorbents capable of trapping organic compounds in the C3-C16 range. Exact sampler configuration depends on thermal desorber system used. See Figure 1 as an example.
Personal sampling pump, 0.01 to 0.05 L/min, with flexible tubing.
Shipping containers for thermal desorber sampling tubes.
Instrumentation: thermal desorption system, focusing capability, desorption temperature appropriate to sorbents in tube (~300° C), and interfaced directly to a GC-MS system.
Gas chromatograph with injector fitted with 1/4" column adapter, 1/4" Swagelok nuts and Teflon ferrules (or equivalent).
Syringes: 1-μL, 10-μL (liquid); 100-μL, 500-μL (gas tight).
Volumetric Flasks, 10-mL.
Gas bulb, 2 L.
NOTE: Prior to field use, clean all thermal desorption tubes thoroughly by heating at or above the intended tube desorption temperature for 1-2 hours with carrier gas flowing at a rate of at least 50 mL/min. Always store tubes with long-term storage caps attached, or in containers that prevent contamination. Identify each tube uniquely with a permanent number on either the tube or tube container. Under no circumstances should tape or labels be applied directly to the thermal desorption tubes.
Calibrate each personal sampling pump with a representative sampler in line.
Remove the caps of the sampler immediately before sampling. Attach sampler to personal sampling pump with flexible tubing.
NOTE: With a multi-bed sorbent tube, it is extremely important to sample in the correct direction, from least to maximum strength sorbent.
For general screening, sample at 0.01 to 0.05 L/min for a maximum sample volume of 6 L. Replace caps immediately after sampling. Keep field blanks capped at all times. Tubes can act as diffusive samplers if left uncapped in a contaminated environment.
Collect a "humidity test" sample to determine if the thermal adsorption tubes have a high water background.
NOTE: At higher sample volumes, additional analyte and water (from humidity) may be collected on the sampling tube. At sufficiently high levels of analyte or water in the sample, the mass spectrometer may malfunction during analysis resulting in loss of data for a given sample.
Collect a "control" sample. For indoor air samples this could be either an outside sample at the same location or an indoor sample taken in a non-complaint area.
Ship in sample storage containers at ambient temperature. Store at -10° C.
Allow samples to equilibrate to room temperature prior to analysis. Remove each sampler from its storage container.
Analyze "humidity test" sampler first to determine if humidity was high during sampling (step 10).
If high humidity, dry purge the tubes with purified helium at 50 to 100 mL/min for a maximum of 3 L at ambient temperature prior to analysis..
Place the sampler into the thermal desorber. Desorb in reverse direction to sampling flow.
Tune the mass spectrometer according to manufacturer’s directions to calibrate.
Make at least one blank run prior to analyzing any field samples to ensure that the TD-GC-MS system produces a clean chromatographic background. Also make a blank run after analysis of heavily concentrated samples to prevent any carryover in the system. If carryover is observed, make additional blank runs until the contamination is flushed from the thermal desorber system.
Maintain a log of thermal desorber tube use to record the number of times used and compounds found. If unexpected analytes are found in samples, the log can be checked to verify if the tube may have been exposed to these analytes during a previous sampling use.
Run spiked samples along with the screening samples to confirm the compounds of interest. To prepare spiked samples, use the procedure outlined in the Appendix.
See Appendix for conditions. MS scan range should cover the ions of interest, typically from 20 to 300 atomic mass units (amu). Mass spectra can either be identified by library searching or by manual interpretation (see Table 2). In all cases, library matches should also be checked for accurate identification and verified with standard spikes if necessary.
The method has been used for a number of field screening evaluations to detect volatile organic compounds. Estimate of the limit of detection for the method is based on the analysis of spiked samples for a number of different types of organic compounds. For the compounds studied, reliable mass spectra were collected at a level of 100 ng per compound or less. In situations where high levels of humidity may be present on the sample, some of the polar volatile compounds may not be efficiently collected on the internal trap of the thermal desorber. In these situations, purging of the samples with 3 L of helium at 100 mL/min removed the excess water and did not appreciably affect the recovery of the analytes on the sample.
|Compound/Synonyms||CAS# RTECS||Empirical Formula||MWa||BPb (°C)||VPc @ 25°C|
mm Hg kPa
|Characteristic Ions, m/z|
|Benzene /benzol||71-43-2 CY1400000||C6H6||78.11||80.1||95.2||12.7||78*|
|Xylene /dimethyl benzene||1330-20-7 ZE2100000||C8H10||106.7||91, 106*, 105|
|Toluene /toluol||108-88-3 XS5250000||C7H8||92.14||110.6||28.4||3.8||91, 92*|
|n-Pentane||109-66-0 RZ9450000||C5H12||72.15||36.1||512.5||68.3||43, 72*, 57|
|n-Hexane /hexyl-hydride||110-54-3 MN9275000||C6H14||86.18||68.7||151.3||20.2||57, 43, 86*, 41|
|n-Heptane||142-82-5 MI7700000||C7H16||100.21||98.4||45.8||6.1||43, 71, 57, 100*,41|
|n-Octane||111-65-9 RG8400000||C8H18||114.23||125.7||14.0||1.9||43, 85, 114*, 57|
|n-Decane /decyl hydride||124-18-5 HD6500000||C10H22||142.29||174||1.4||0.2||43, 57, 71, 41, 142*|
|Acetone /2-propanone||67-64-1 AL3150000||C3H6O||58.08||56||266||35.5||43, 58*|
|2-Butanone /methyl ethyl ketone||78-93-3 EL6475000||C4H8O||72.11||79.6||100||13||43, 72*|
|Methyl isobutyl ketone /MIBK, hexone||108-10-1 SA9275000||C6H12O||100.16||117||15||2||43, 100*, 58|
|Cyclohexanone /cyclohexyl ketone||108-94-1 GW1050000||C6H10O||98.15||155||2||0.3||55, 42, 98*, 69|
|Methanol /methyl alcohol||67-56-1 PC1400000||CH3OH||32.04||64.5||115||15.3||31, 29, 32*|
|Ethanol /ethyl alcohol||64-17-5 KQ6300000||C2H50H||46.07||78.5||42||5.6||31, 45, 46*|
|Isopropanol /1-methyl ethanol||67-63-0 NT8050000||C3H7OH||60.09||82.5||33||4.4||45, 59, 43|
|Butanol /butyl alcohol||71-36-3 E01400000||C4H9OH||74.12||117||4.2||0.56||56, 31, 41, 43|
|Butyl cellosolve /2-butoxyethanol||111-76-2 KJ8575000||C6H14O2||118.17||171||0.8||0.11||57, 41, 45, 75, 87|
|Diethylene glycol ethyl ether /Carbitol||111-90-0 KK8750000||C6H14O3||134.17||202||0.08||0.01||45, 59, 72, 73, 75, 104|
|Phenol /hydroxybenzene||108-95-2 SJ3325000||C6H5OH||94.11||182||47||0.35||94*, 65, 66, 39|
|Cresol||1319-77-3 G05950000||C7H7OH||108.14||108*, 107, 77, 79|
|Methylene chloride /dichloromethane||75-09-2 PA8050000||CH2Cl2||84.94||40||349||47||86*, 84, 49, 51|
|1,1,1-Trichloroethane /methyl chloroform||71-55-6 KJ2975000||CCl3CH3||133.42||75||100||13.5||97, 99, 117, 119|
|Perchloroethylene /hexachloroethane||127-18-4 KX3850000||CCl3CCl3||236.74||187 (subl)||0.2||<0.1||164*, 166, 168, 129, 131, 133, 94, 96|
|o-,p-Dichlorobenzenes||C6H4Cl2||147.0||146*, 148, 111, 113, 75|
|1,1,2-Trichloro-1,2,2- trifluoroethane /Freon 113||76-13-1 KJ4000000||CCl2FCClF2||187.38||47.6||384||38||101, 103, 151, 153, 85, 87|
|d-Limonene||5989-27-5 OS8100000||C10H16||136.23||176||1.2||68, 67, 93, 121, 136*|
|Turpentine (Pinenes)||8006-64-2||C10H16||136.23||156 to 170||4 @ 20"||93, 121, 136*, 91|
|Hexanal /caproaldehyde||66-25-1 MN7175000||C6H12O||100.16||131||10||1.3||44, 56, 72, 82, 41|
|Benzaldehyde /benzoic aldehyde||100-52-7 CU4375000||C7H12O||106.12||179||1.0||0.1|
|Nonanal /pelargonic aldehyde||124-19-6 RA5700000||C9H18O||142.24||93||23||3||43, 44, 57, 98, 114|
|Ethyl acetate /acetic ether||141-78-6 AH5425000||C4H8O2||88.1||77||73||9.7||43, 88*, 61, 70, 73, 45|
|Butyl acetate /acetic acid butyl ester||123-86-4 AF7350000||C6H12O2||116.16||126||10||1.3||43, 56, 73, 61|
|Amyl acetate /banana oil||628-63-7 AJ1925000||C7H14O2||130.18||149||4||0.5||43, 70, 55, 61|
|Octamethylcyclotetra- siloxane||556-67-2 GZ4397000||C8H24O4Si4||296.62||175||281, 282, 283|
|a Molecular Weight|
|b Boiling Point|
|c Vapour Pressure|
|*Indicates molecular ion|
Tube desorption temperature: 300°C
Tube desorption time: 10 min.
Valve/transfer line temperatures: 150°C
Focusing trap: Carbopack B/Carboxen 1000, 60/80 mesh, held at 27°C during tube desorption
Focusing trap desorption temperature: 300°C
Desorption flow: 50-60 mL/min.
Inlet split: off
Outlet split: 20 mL/min.
Helium: 10 PSI
DB-1 fused silica capillary column, 30 meter, 1-μm film thickness, 0.25-mm I.D. Temperature program: Initial 35°C for 4 min, ramp to 100°C at 8 /min, then ramp to 300°C at 15 /min, hold 1-5 min.
Run time: 27 min.
Transfer line: 280°C
Scan 20-300 amus, EI mode
EMV: set at tuning value
Solvent delay: 0 min for field samples; if a solvent-spiked tube is analyzed, a solvent delay may be necessary to prevent MS shutdown caused by excessive pressure.
Alternative methods may be obtained adapting, for instance, NIOSH Method 1500 (Hydrocarbons b.p. 36 – 216°C) or NIOSH Method 1501 (Hydrocarbons, aromatic).
Main differences – not fundamentals – may consist in: sorbent choice (charcoal tube), desorption technique (elution with CS2), sampling time (longer than in workplaces) and other. More important is the possibility of using diffusive (passive) samplers.
5. Passive sampling
The original purpose of the development on passive sampling (based on Fick’s laws) is to provide technology at low cost, enabling air quality surveys to be routinely executed at multiple locations within urban and rural areas, industrial sites and forests. This requires the examination of the performance characteristics of the diffusive sampler over long sampling periods, in comparison with established methods, and in practical applications of urban monitoring (Brown et al., 1994; Brown et al., 1999). Several authors proposed the use of different models of diffusive (passive) devices (Brown, 1993; Harper, 2000; Bertoni et al., 2001; Brown, 2002; Kot-Wasik et al., 2007) conceived for the determination of long-term averaged concentration of some airborne volatile and semi-volatile organic compounds, relevant on the human health protection (VOCs, polycyclic aromatic hydrocarbons and nicotine). The diffusive sampling technique is known to be the cheapest and easiest way to perform extensive sampling campaigns, both in temporal and spatial terms. Moreover, this is the only collection technique allowing the true separation of the vapour phase species from the particle bound fraction (Bertoni et al., 2004; Namiesik et al., 2005).
A lot of different models of passive sampler have been proposed by many researchers; in this chapter we can show only a “classic” sampler (Analyst, developed by the Italian National Research Council, IIA-CNR, Figg. 2 and 3) and a more recent sampler, based on radial diffusion principle (Ring, IIA-CNR, Fig. 4).
6. Data evaluation and exposure risk assessment
Studies have found that home levels of several organics average 2 to 5 times higher indoors than outdoors. During and for several hours immediately after certain activities, such as paint stripping, levels may be 1,000 folds background outdoor levels. Despite direct reading instruments can be used (like the IR used in indoor monitoring shown in Figure 5), as above mentioned, currently it is better to try to obtain very low LODs and LOQs by employing sampling methods as described.
Sometimes they are used Threshold Limit Values (TLVs) that are the guideline values set by the American Conference of Governmental Industrial Hygienists (ACGIH) to minimize workers exposure to hazardous concentrations as much as possible. The TLVs are published yearly for more than 700 chemical substances and physical agents (ACGIH, 2010). This use is incorrect and unauthorized by ACGIH, because the TLVs respect is not a warranty of no health effects, that is on the contrary a fundamental requirement in nonindustrial environment.
No standards have been set for VOCs in non-industrial settings. OSHA regulates formaldehyde, a specific VOC, as a carcinogen. OSHA has adopted a Permissible Exposure Level (PEL) of 0.75 ppm, and an action level of 0.5 ppm. Based upon current information, it is advisable to mitigate formaldehyde that is present at levels higher than 0.1 ppm. Recently the World Health Organization (WHO, 2010) provided health-based guidelines for 55 airborne inorganic and organic compounds for carcinogenic and non-carcinogenic health endpoints. The non-carcinogenic endpoints include development toxicity, reproduction toxicity, respiratory toxicity, neurotoxicy, hepatoxicity, hematoxicity, eye/nose/throat irritation, and odor annoyance. The lowest concentration at which effects are observed in humans, animals, and plants was used as a staring point for the non-carcinogenic endpoints. Uncertainty factors determined through scientific judgment in consensus and averaging time were also taken into account in determining the health endpoint for non-carcinogenic compounds. The classification by the international Agency for Research on Cancer (IARC) was used to determine a chemical as a carcinogen. The endpoint of carcinogen was determined by linear extrapolation from the high dose level, which is characteristic of animal experiments or occupation exposure with cancer responses.
This objective requires measurements for checking whether specified limit or guideline values are being exceeded. Examples of limit and guideline values (except workplace atmospheres and ambient air) for indoor environments are given in Table 3 and 4, established by the ad hoc committee of IRK/AOLG of Germany for organic chemicals.
|Tetrachloroethene||Germany||0.1 mg/m3||7 days|
|Pollutant||Country/Organisation||Guideline Value||Averaging Time|
|Formaldehyde||Germany||0.12 mg/m3||not specified|
|Nitrogen dioxide||Germany||60 μg/m3 a||7 days|
|Toluene||Germany||0.3 mg/m3 a||not specified|
|Styrene||Germany||0.03 mg/m3 a||7 days|
|Dichloromethane||Germany||0.2 mg/m3 a||24 h|
|TVOC||Germany||0.2 – 0.3 mg/m3||not specified|
|a Guideline value (RW I-value, "Richtwert I"= guideline value I) aimed at hygienic prevention.|