The Utilization of C, Cl and H Isotopes in Vapor Intrusion Studies as a Tool for Determining Sources of Indoor VOCs

摘要

There are many aspects to vapor intrusion studies but one extremely important issue is determination of the source of the indoor volatile organic compound(s) (VOCs). The source compounds (VOCs) in indoor air could be caused by both sub-surface (vapor intrusion) or indoor sources (i.e. household chemicals) making the source determination of the actual vapor intrusion hazard very complicated. Currently, the most common approaches for identification of indoor sources of VOCs during vapor intrusion investigations are: i) visual building surveys for known indoor sources; and ii) room-by-room measurements of VOC concentrations. Both of these approaches have limitations. Compound specific isotopic analysis (CSIA) will be presented as an alternative method of VOCs source discrimination. CSIA permits determination of isotope ratios of the contaminants of concern. CSIA provides direct means for direct individualization of the contaminants by their isotope ratios. Contaminants sourced from different feedstocks, different synthetic pathways and/or having different attenuation histories in many cases will have different isotopic signatures that can subsequently be used to differentiate sub-surface and indoor sources. CSIA of carbon, chlorine and/or hydrogen isotopes can be combined to provide more a powerful individualization tool. This paper presents the methodology and the principles of application of CSIA in vapor intrusion assessment. The first part will describe validation of vapor VOCs sample collection protocol. By application of active adsorbent sampling, VOCs at concentrations as low as 1 ug/m3 can be analyzed. Secondly, the actual methods for determination of C, H and Cl isotopes in VOCs will be discussed, followed by application of CSIA to selected cases studies. Utilization of stable isotopes is not necessarily the silver bullet to vapor intrusion studies but it provides a major step forward in identifying potential sources of indoor VOCs.