Human Exposure Assessment for Airborne Pollutants Advances and Opportunities (1991) / Chapter Skim
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3 Sampling and Physical-Chemical Measurements
3 Sampling and Physical-Chemical Measurements
Pages 53-114
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From page 53... ...
In assessing human exposures to airborne pollutants, numerous factors besides the contaminant must be measured especially if the assessment is based on fixed-site sampling or modeling. Accurate estimates in these instances depend not just on concentration measurements from f~xed-site monitors in various locations, but also ore knowledge of numerous factors that influence the environments where the exposures occur (see Chapter 2~.
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From page 54... ...
Emissions of various airborne contaminants can be time dependent. For example, at a manufacturing site, time of day and day of week can influence emission rates and, consequently, the airborne concentrations of various species.
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From page 55... ...
For environmental measurements, QC comprises operational activities that are carried out before and during the measurement process that are intended to ensure that data are of sufficient quality~ata whose precision and accuracy are known and are sufficient to meet the needs of ~ study. Examples of QC are calibration procedures, maintenance of constant line voltage and temperature, use of blank and spiked samples, and use of traceable standard reference materials.
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From page 56... ...
56 3 Cal _' 4 o C)
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From page 57... ...
Site-Selection Errors The representativeness of the sampling site refers to selection for appropriate spatial and temporal definition. For example, a study to determine compliance with ~ ambient air~qu;ality steward for ~ given pollutant would require air samplers to be placed at community sites that represent typical outdoor air and to have the same measurement time as the standard.
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From page 58... ...
Although passive samplers might seem to alleviate many of these problems, an outer garment over the device seriously reduces sampling capability. Therefore, the design of personal samplers should include provisions to minimize their misuse and to ensure that they have been used properly.
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From page 59... ...
Designing a measurement strategy for a field study seems straightforward, but designing one that minimizes the errors almost always is difficult. Further, designing a good QA program for environmental field measurements might be more difficult than one designed for laboratory experiments.
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From page 60... ...
The partitioning can result from the adsorption of a vapor-phase compound onto the surfaces of airborne particles, in which case the contaminant distribution is a function of the compound's liquid-phase (or subcooled liquid phase if the compound is a solid at ambient temperature) vapor pressure and also the surface area of airborne particles per unit volume of air (Pankow, 1987; Bidleman, 1988; Junge, 1977; Ligocki and Pankow, 1989~.p,p'-Dichlorodiphenyltrichloroethane is an example of an ambient contaminant commonly partitioned in this manner.
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From page 61... ...
are integral to a thorough evaluation of the health effects of certain pollutants. The water content of airborne particles can affect partitioning of an inorganic gas between the vapor and condensed phases.
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From page 62... ...
It is also important to ensure that the measurement procedure does not alter the water content. However, in some situations, protocols might require that the measurement be made at a specified RH.
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From page 63... ...
63 g ._ as o v g ·_ a: o : o Ct o .
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From page 64... ...
However, chromatographic separations can be time consuming and require each analysis to be discrete. For example, in a continuous analysis for total aromatic compounds, the compounds can be fed directly into a photoionization detector (PID)
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From page 65... ...
, then shorter sampling times can be used to achieve the necessary temporal resolution. This approach must be tempered with the knowledge that subsequent analyses are expensive, and the cost of the total analyses might be prohibitive.
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From page 66... ...
The unit should also be rugged, because it might need to endure extreme conditions of heat, humidity, and shock. In addition to personal sampling, there is a continuing need for portable methods for air analysis that could be deployed in a variety of field settings (e.g., portable gas chromatography and mass spectrometers)
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From page 68... ...
In many analytical procedures, two of the rings overlap; the overlap most frequently encountered is between separation and detection. For example, in GC with flame-ionization detection, one instrument combines the separation step (GC)
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From page 69... ...
Passive sampling sometimes referred to as diffusive samplin~relies on diffusion to deliver airborne contaminants to the collection medium.
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From page 70... ...
-sample collection devices can be sent and returned in this fashion. Passive samplers are favored for personal monitoring; they are lighter, smaller, and less likely to interfere in daily activities than are active samplers.
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From page 71... ...
. Active Sampling Although passive sampling is well suited to vapor-phase pollutants, active sampling can be used for this as well as condensed-phase contaminants.
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From page 72... ...
of ambient air and ambient air from which ozone has been removed selectively. The latter uses light scattering to monitor the number concentration versus diameter of airborne particles.
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From page 73... ...
However, the size of airborne particles is an important factor in estimating potential human exposures, which argues for including size-fractionation as part of any procedure that samples airborne particles. Furthermore, chemical composition and biological activities are related to particle size (Phalen et al, 1986~; these size ranges are based on the inhalation of particles by humans.
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From page 74... ...
Sampling of airborne particles in more than two size ranges usually is conducted with a cascade impactor. This device is simply a set of impactors, operating in series, arranged in order of decreasing cutoff size.
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From page 75... ...
Separation Chromatography Chromatography is a separation process often used to isolate airborne contaminants from other compounds that might interfere in detection of specified contaminants. Chromatography involves the simple partitioning of analytes between mobile and stationary phases.
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From page 76... ...
Because the separation process involves compounds in the gas phase, GC is ideal for the analysis of many airborne contaminants. The National Institute for Occupational Safety and Health (NIOSH)
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From page 77... ...
has led to techniques to sample automatically from several gas containers (Blacha et al., 1988~. Furthermore, the combination of GC with mass spectrometry has made this a very popular tool for both the qualitative and quantitative analysis of a wide range of airborne contaminants.
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From page 78... ...
This increases instrument cost and, in some cases, increases its size and weight, making it less portable, although portable gas chromatography now are available that are capable of limited temperature programming. As chromatography become smaller alla smaller, a "gas chromatograph on a microchips could be fashioned (Angell et al., 1980; Overton et al., 1988~.
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From page 79... ...
IC is used routinely to identify and quantify the major anions and cations associated with airborne particles, including sulfate, nitrate, chloride, ammonium, sodium, potassium, magnesium, and calcium. For all types of LC, the analyses of interest are dissolved in the mobile phase and then pass through a column packed with the stationary phase.
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From page 80... ...
TLC,s main application to the analysis of airborne contaminants is for the analysis of semivolatile compounds present on airborne particles that are small enough to be taken into the lung. A typical application would be for the separation of polycyclic aromatic hydrocarbons (PAHs)
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From page 81... ...
LC needs a universal detector comparable to the GC flameionization detector. Techniques are available to interface LC to mass spectrometry, and their development and application will complement, but not replace, GC as the primary chromatographic tool for the analysis of airborne contaminants.
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From page 82... ...
Packed columns suffered from limited resolution, and the high mobile phase flow rates made detector interfacing difficult. SFC has been successfully interfaced to numerous detectors, including GClike detectors, such as flame ionization, flame photometric, thermionic, microwave plasma, and electron capture detectors, as well as mass spectrometers, and Fourier transform IR spectrometers.
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From page 83... ...
These materials often are used in particulate sampling devices, as protectors or limiters for passive sampling devices, and in electrochemical sensors to keep the electrolyte in but allow exposure to a gaseous analyte. Nonporous Teflon membranes are used in oxygen sensors to separate oxygen from a variety of potential interferents.
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From page 84... ...
Supercntical Fluid Extraction Supercritical fluids can be used to desorb trapped airborne contaminants from various absorbents. VOCs and semivolatile organic compounds
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From page 85... ...
Thus, the Resorption process can also become a selective extraction process. The use of supercritical fluids for extraction and chromatography deserves greater research attention in the assessment of airborne contaminants.
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From page 86... ...
This method of sample preparation is extremely thorough and shows the degree of sample preparation steps that may be necessary to analyze airborne contaminants. It also illustrates how simple LC and the more elaborate HPLC can be used for the preparation of samples for subsequent analysis.
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From page 87... ...
O CO2 or water, which makes it ideal to analyze trace-level organics in ambient air.
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From page 88... ...
The nitrogen hall respond to TID, but any Interfering compounds that are not derivatized uphill not respond to TID unless they originally contained nitrogen. This provides enhanced sensitivity and selectivity for the desired analyte.
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From page 89... ...
GC-MS is particularly well suited to the analyses of airborne contaminants, but is limited by requiring that the analyses be thermally stable and volatile under GC conditions. This restricts the usefulness of GC-MS when analyzing metals, metal salts, high molecular-weight compounds and compounds susceptible to thermal decomposition.
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From page 90... ...
The mass spectrometer is capable of distinguishing these surrogates from the original analyte, because the surrogates differ in mass. The surrogates are particularly useful for accurate quantitation (Lewin et al., 1987~.
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From page 91... ...
Many of these features are incorporated into a new type of mass spectrometer, the ion trap mass spectrometer. This new and innovative device might resolve many of the disadvantages of present MS units.
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From page 92... ...
The ion trap detector (ITD) is a new type of MS system.
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From page 93... ...
The IMS has the advantage of operating at atmospheric pressure, which eases the operational problems associated with mass spectrometers, which normally operate at reduced pressures. The IMS has shown sensitivities of less than 1 ppb and good response times (0.1 to 10 seconds)
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From page 94... ...
Miniature, inexpensive, microfabricated ion-sensitive devices have also been introduced (Lauks and Zemel, 1979) , and combination of the field effect transistor (FET)
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From page 95... ...
materials in the field or laboratory Their use in exposure assessment is not widespread. Amperomet~y Amperometric defies have been used in exposure assessment studies as personal monitors and area monitors (Hartwell et al., 1984; Leslie et al., 1990~.
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From page 96... ...
These characteristics make electrochemical approaches ideal for field use and direct measurement of human exposure to airborne pollutants. The challenge for electrochemical crevices is the attainment of adequate analytical performance in a practical field situation; combined sensitivity, selectivity, stability, lifetime, and ruggedness are needed.
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From page 97... ...
A number of simple and inexpensive luminescence techniques have been developed recently and applied to the analyses of airborne pollutants. These include synchronous luminescence and room-temperature phosphorescence (RTP)
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From page 98... ...
GC-matrix-isolation/FTIR is being used for the qualitative analysis of airborne contaminants (Childers et al., 1987~. The technique complements qualitative GC-MS analyses by providing additional structural information about matrix-isolated compounds.
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From page 99... ...
Capacitive sensors for humidity are also possible using a device called the charge flow transistor. The SAW (surface acoustic wave elements)
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From page 100... ...
Spectral "fingerpnnt" Surface-enhanced Raman spectromet~y Electromagnetic properties sensors: active Nonlinear behavior, including frequenter doubling Fluorescence Source: Developed from a presentation made by J Zemel at the "Workshop on Advances in Assessing Human Exposure to Airborne Pollutants," Yale University, October 19-20, 1988.
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From page 101... ...
~ addition to chemical sensing, advances ~ microengineering Include mecllanical devices such as pumps, balances, gears, wheels, springs, valves, motors, and similar mechanical structures that are micron-dimension. The application to small field samplers and exposure assessment in the future seems appropriate, but these new technologies have not been applied toward use in exposure measurements.
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From page 102... ...
From the physical size and density, an aerodynamic diameter can be calculated. Thus, the CCSEM provides size, shape, and elemental composition data for each particle.
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From page 103... ...
, and environmental samples (water, airborne particles, street dust, and fly ash)
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From page 104... ...
is another common multielement method for aerosol samples. A good discussion of XRF applied to the analyses of airborne particles is presented in Malissa and Robinson (1978~.
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From page 105... ...
The radon is adsorbed on the carbon and acc~nulates over time. After the sampling period is over, the canister is sealed, and the decay products build up in the container.
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From page 106... ...
The decay-product behavior is quite complex because of the ability to attach to airborne particles, as well as to indoor surfaces such as walls, ceilings, and furnishings. The particle size determines the ability of the radioactivity to be deposited in the room and In the respiratory system.
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From page 107... ...
One immediate application is in the analysis of data from several sensors, where qualitative and quantitative analysis can be performed on the air sample (Stetter, 1986~. These methods can be used to resolve and quantitate the components of mixtures that the separation methods do not separate fully.
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From page 108... ...
When applied to resolving sources of airborne particulate matter or applications to interpreting airborne mutagenicity, chemometric methods commonly are called receptor models and are discussed more fully in Chapter 6. SUMMARY In assessing human exposures to airborne pollutants, numerous factors besides the contaminant must be measured, especially if the assessment is based on fixed-site sampling or modeling.
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From page 109... ...
is the most direct approach for assessing human exposure to airborne pollutants. However, the portability requirement of this technique typically decreases method sensitivity compared with stationary microenvironmental monitoring.
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From page 110... ...
Some contaminants are not distributed uniformly over the surfaces of airborne particles. To evaluate health effects properly, particulate analyses
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From page 113... ...
These include more portable, reliable, and rugged gas chromatographs, gas chromatograph/mass spectrometers, and ion trap mass spectrum eters. Sampling methods, instruments, and software that interfaces with such instruments are also needed to permit unattended sample collection and analyses in field settings.
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