Written by:
Prism Analytical Technologies, Inc.
Reprinted with permission of Indoor Environment Communications.
Excerpted from Volume 8, Issue 10 • August 2007
Copyright © 2007. All Rights Reserved.
In the somewhat tumultuous history of the science of indoor air quality, homeowners, business owners and the general public have been beset by alarms one after the next. There always seems to be a crisis du jour. References to poor IAQ date back to ancient Greece and Rome but the problem probably existed back to the time of the cavemen; however, the recorded history for this period is sparse. Of late, IAQ issues have included, among other things, formaldehyde in carpets and foam insulation, asbestos, air "ionization," ozone insertion, radon, mold, soil vapor and now volatile organic compounds in general. Some of these issues are real, some imagined, some handled scientifically and expeditiously, some exaggerated and most exploited in some way or another by hysteria-mongering charlatans. The objective of this discourse is to shed some light on the issue of VOCs from a chemist's perspective to help dispel some of the myths surrounding them and to help IAQ investigators tackle this dimension of their work.
Even the term "volatile organic compounds" sounds rather daunting to an individual without a degree in chemistry or a lot of experience because measurement and interpretation of VOCs is wholly different from nearly all other IAQ measurements. Radon, CO2, humidity, etc. are just what they say they are and no interpretation is required. Not so with VOCs. What is measured are chemical compounds with strange sounding names like geraniol, citronellyl formate and limonene, which must be translated into Japanese Beetle attractant, rose scent and citrus, respectively. Even after the translation has been made, interpretation is required to answer questions such as: "What is a normal level for this compound?" "Is this level hazardous?" and "Do I need to do something to manage it and, if so, what?" As complex as this issue appears, it can be simplified by understanding a few basic concepts.
There are many "hand-held" on site monitors that can be useful on occasion, but they have limited utility, especially in addressing odor problems. The most effective way to assess VOCs is to take a sample and send it to a laboratory for analysis, usually performed using gas chromatography-mass spectrometry (GC-MS). This technique has the advantage of separating the VOCs from each other and then using the MS fingerprints (cracking patterns) of the compounds to determine their identity. While GC-MS is the principal workhorse for this analysis, Fourier transform-infrared (FT-IR) Spectrometry has also been used effectively to augment the GC-MS analysis because of its wide dynamic range and its effectiveness at identifying simple organics that do not have a singular, well-defined mass spectral fingerprint.
The first step in understanding VOCs is to get a feel for total VOCs, or TVOCs,, the sum of all VOCs present. TVOC should not to be confused with the simple sum of all identified compounds in the chromatogram. Many sources of VOCs produce a vast array of low-level overlapping peaks that, when viewed in a chromatogram, appear to be a "hump" as shown on the right hand side of Figure 1. The most common sources of these "humps" include fuels (gasoline, kerosene, or diesel), paints and varnishes, natural gas, low-quality solvents, decaying organic matter and rotting flesh. These "humps" can make up a very significant fraction of the TVOC load and should not be ignored.
Setting aside the impact of individual compounds for now, the TVOC load can have significant deleterious effects on building occupants. Currently, there is no specific U.S. standard for the permissible exposure level for TVOC. Even though research and opinions have been published for more than 30 years, questions regarding safe levels or whether or not methane, ethane and similar low molecular weight compounds should be included still remain and are currently being debated. However, it is still possible to establish reasonable, workable limits for TVOCs. The LEED (Leadership in Energy and Environmental Design, USGBC) has set the standard for Green Buildings at less than 500 nanograms per liter. The European Community has established a TVOC limit of 300 ng/L with no single compound contributing more than 10 percent of the total. One U.S. chemical company uses the standard of less than 500 ng/L as their target for nonmanufacturing areas, 500.- 1,000 ng/L as their "action level" and greater than 1,000 ng/L as their "immediate action level." The literature generally seems to agree that less than 300 ng/L represents an "acceptable" TVOC level and that greater than 3,000 ng/L represents a "hazardous" TVOC level; however, few seem to want to address the hazards involved with levels between 300 and 3000 ng/L.
The recognized symptoms above 3,000 ng/L generally include drowsiness, eye and respiratory irritation, general malaise, headache, nausea and exacerbation of symptoms of respiratory ailments. Some data suggest that high TVOC levels amplify the hazardous effects of specific harmful VOCs. In addition, there is some empirical information from industrial hygienists who perform medically driven environmental investigations that indicates typically acceptable levels are too high by a factor of two or more for chemically sensitive individuals.
Table 1 was developed using available literature, data from numerous companies and industrial hygienists active in the IAQ field, together with empirical data from many personal investigations. It provides a workable definition of the limits and effects of C3-C15 TVOC concentrations and has proven to be a good predictor of the level of expected symptoms of non-chemically sensitive people. The next step in understanding VOCs is to consider collections of compounds that give indications of the five most common VOC problems: gasoline, paint, odorants, personal care and lifestyle.
Gasoline has six marker compounds associated with it. They are benzene, toluene, ethylbenzene and the three xylene isomers. The source of gasoline can be ambient air (especially in urban environments), but it is generally the office occupants themselves who supply the contamination. Remember that for every gallon of gas pumped into an automobile, one gallon of air saturated with gasoline vapor is dumped into the lap of the person filling the tank. This person then goes to the office and off gasses the rest of the day. The gasoline levels in homes are generally higher than in offices because, in addition to the personal off gassing, the most common source of gasoline vapors is the collection of gas cans, mowers, trimmers, etc. in the attached garage.
Paints are very complex and can have several different markers, but they typically include methylcyclohexane, substituted cyclics, butylcellosolve, substituted alcohols, unsaturated C9-C12 hydrocarbons and the straight-chain hydrocarbons nonane (C9) through dodecane (C12). Paint VOCs can linger at significant levels for as long as 18months after application; however, even though the paint may be fully cured, leaking paint cans often contribute to the VOC load for years.
Odorants are chemicals that are supposed to smell good. They are in air fresheners, potpourri, scented oils, perfumes/colognes and nearly all cleaning and personal care products. In a typical office, especially in an office or home where an IAQ problem exists that the occupants think they can eliminate by covering it up, odorants can make up a significant fraction of the TVOC load. These odorants include many aldehydes, alcohols, ketones, pinenes and complex esters.
Personal care products are the primary sources of acetone, typically associated with nail care (nail polish remover is nearly 100 percent acetone). Other compounds associated with personal care include the C2-C5 acetates (nail care), isopropanol and ethanol (cosmetics and hair spray) and menthol, camphor, and methylsalicylate (topical ointments).
Lifestyle chemicals are many and varied, but the three primary compounds are ethanol from antiseptic wipes (although the occasional leaking bottle of scotch cannot be ruled out), tetrachloroethylene or PCE from garments that have been dry cleaned and 1,4-dichlorobenzene from mothballs.
What has been presented thus far serves as a primer of sorts but covers only 25-50 percent of the problems that will be encountered in the real world. The rest are far more complex and require close cooperation between the laboratory and the investigator. For example, consider a four-story apartment building constructed in the early 1920s in which sulfur dioxide is indicated in the analysis. When it was built, the apartment was equipped with centrally pressurized refrigerant, which was piped to each apartment to cool the refrigerator. Guess what was used as the refrigerant. After electric refrigerators became commonplace, the compressor and piping were sealed off and walled over. Corrosion due to a water intrusion event formed a pinhole in one of the pressurized pipes, releasing sulfur dioxide into the building. Or consider the asthmatic child of a wealthy couple. The plasticizer used in the hordes of plastic toys with which the child was playing was causing his asthma attacks.
When assessing VOC contamination, the general tendency is to run a USEPA TO-15 or TO-17 analysis; however, experience has shown that this type of analysis will solve fewer than 10 percent of the VOC problems typically encountered because fewer than 75 compounds are typically reported (at many laboratories, fewer than 50 compounds) and they are mostly substituted benzenes and halogenates. By far, the better analysis is a full spectrum analysis. Thermal desorption tubes generally provide the best collection medium for this purpose because of their small size, long shelf life, broad versatility and low acquisition, storage and shipping costs. In addition, they can be applied to other analytical techniques such as FT-IR. Recent advances in FT-IR technology coupled with the fact that VOCs from 40 L of air can be trapped on a tube and desorbed into a 1 L IR cell work together to expand the effective range of FT-IR down to the 1-10 ppb range. But by far the most attractive attribute of thermal desorption tubes is their ability to quantitatively trap compounds that are generally considered to be semivolatiles. These include the diesel/kerosene markers (naphthalene and the methylnaphthalene isomers), medicinal compounds (camphene, menthol and methylsalicylate), phenolics (including the cresols) and many characteristic odors and scents including compounds like citronellyl acetate (rose), eugenol (clove), cedrol (cedar or sandalwood), geosmin (fungal and musk), á- Cedrene (exotic woods) and skatole (fecal material).
NIOSH 2549 is an excellent method for thermal desorption tube analysis. A great deal of credit goes to NIOSH for writing a performance-based method rather than a detailed cookbook that is outdated before it is promulgated. In addition to the compounds they report quantitatively, most laboratories that use this method to perform a full spectrum analysis will determine many of the compounds they report semiquantitatively - i.e., the concentration is estimated rather than based on a calibration curve. Usually, though, this level of accuracy is sufficient to determine the source(s) of VOC contamination.
At this point, a discussion is warranted as to how the identification of compounds reported semiquantitatively is made. There is a distinct difference between running a computer-generated library search to identify compounds in a full spectrum analysis and having the analysis performed by a competent chemist well trained in mass spectral interpretation and who has available a large in-house collection of reference compounds. Any laboratory can produce a report based on a computer generated library search in under a minute. Virtually no operator training is required. However, what appears to be an effective application of computer technology frequently results in incorrect compound identification. Misidentification causes several problems. When a hazardous compound is erroneously cited, it can mandate unnecessary and expensive follow-up testing, cause grave concern when it is unwarranted and embarrass the investigator. Equally problematic is failing to correctly identify critical compounds. Misidentification arises primarily because every computer generated library search routine selects a single best match - oftentimes, the second best match, which may be the correct compound, is only minutely lower in search quality. Also, different search criteria result in different best matches, or the computer may select an outlandish compound totally inconsistent with the retention time, fail to account for distorted mass spectra or fail to differentiate overlapping compounds. This uncertainty is seldom, if ever, transmitted to the submitter as part of the analytical report. As a result, the submitter has no idea whatsoever of the validity of the results.
A good laboratory report should give the name of the compound, synonyms, the concentration determined in weight/volume as well as ppb, comments by the analyst (including uncertainty in identification), the molecular weight of the compound and the Chemical Abstract Service (CAS) number. The CAS number is critical when searching the Web for information on a specific compound. For example, 4-methyl-2- pentanone can be called MIBK, or methyl isobutyl ketone, but it has only one CAS number, 108-10-1. Then, the only problem in searching the Web will be sorting through a few old hockey win/loss records. In addition, the laboratory report should include hydrocarbons, even if their exact structure cannot be determined, because their presence constitutes a hydrocarbon fingerprint that is very useful in chemical profile interpretation and comparisons among samples.
With all the intricacies of sampling (media, sampling parameters), laboratory analysis (type of instrument, choices of analytical parameters), translation (translating chemical compounds into substances, materials and products) and chemical profile interpretation (figuring out what the analysis means in practical terms), it is critical that a laboratory be selected that is capable of working with the investigator in all phases of the project, including everything from planning the very start of the project through the chemical profile interpretation. Choose your laboratory carefully!
