Research Program Area: Health & Exposure
There is an increased concern facing federal and state health officials regarding the risk of public exposure to toxic air contaminants in indoor environments. The immediate interest concerns the indoor exposure to polycyclic aromatic compounds (PAC), many of which are potent carcinogens with known indoor sources. Current outdoor sampling and analytical techniques require collection of a large volume of air using a high volume sampler which is not appropriate for use indoors, since the high sampling flow rates required would substantially alter the indoor environmental conditions and thus introduce a large uncertainty into the assessment of the actual indoor concentrations. Thus, the California Air Resources Board has commissioned research to develop an indoor sampling and analysis method for airborne PAC. We developed a new sampler for measuring particulate and gas phase PAC in indoor environments. The sampler consists of a fan cooled acoustically insulated pump which draws air through a sampling cassette composed of a 47 mm TIGF filter followed by a sorbent cartridge packed with XAD-4 resin. It is relatively unobtrusive with a noise level comparable to a personal computer or refrigerator. The flow rate of the sampler in the field tests was set to approximately 34 liters per minute so that a 25 m3 sample volume could be collected in a 12-hour period. The 25 m3 sample volume is necessary to achieve the desired ng / m3 detection limit for PAC without significantly impacting the indoor concentrations.
A sampling and analytical method for gas-phase polycyclic aromatic hydrocarbons (PAH) was developed specifically for use in indoor air. Samples were collected on sorbent samplers containing two sections of XAD-4 resin, each weighing 2.5 g. The XAD-4 resin was extracted in dichloromethane in an ultrasonic bath, concentrated, and 14 PAH were analyzed for by electron impact gas chromatography-mass spectrometry. Perdeuterated internal standards for quantitation were added to the extracts immediately prior to the analyses. The limit of detection for compounds without measurable blank values was estimated to be -0.1 ng / m3 for a sample volume of 25 m3 . We also developed an analytical method for gas-phase nitro polycyclic aromatic hydrocarbons (nitro-PAH) in samples of indoor air. This method was used for the analysis of 1 -nitronaphthalene and 2 -nitronaphthalene in extracts of the front sections of sorbent samplers used to collect gas-phase PAH. An extraction and analysis method was developed for determination of particulate-phase PAH in indoor air using HPLC with gradient elution, flow programming and selective fluorescense detection. Twenty-one semi-volatile and particulate-phase PAH were determined, with levels of detection ranging from 0.28 ng / m3 for retene to 0.001ng / m3 for dibenzo(a, h)pyrene. The detection limit for benzo(a)pyrene was 0.018 ng / m3 . Two fluorescence programs were devised to determine closely-eluting and co-eluting pairs in two injections per sample.
The precision of this newly developed indoor PAC sampler was evaluated in a pilot field study conducted in three residences and two commercial buildings. The PAC sample pumps performed quietly and reliably throughout the PAC pilot field study. The indoor concentrations of gas-phase PAH were generally higher indoors than outdoors which is consistent with the presence of known indoor PAH sources in this study. In one residence without any indoor combustion sources, there were many gas-phase PAH with significantly higher indoor concentrations suggesting the presence of indoor sources not directly combustion related. The concentrations of particulate-phase PAH were not as different from the outdoor concentrations as were the gas-phase PAH. From this pilot PAC field study we have concluded that the indoor PAC sampler and analytical methods are ready for deployment in a larger field study for most of the gas-phase PAH measured in this study but not for the particulate-phase PAH or the gas-phase nitro-PAH. The analytical methods for these compounds will require some further development to improve measurement precision before deployment in a large indoor field study.
For questions regarding this research project, including available data and progress status, contact: Research Division staff at (916) 445-0753
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