The Application of TO-15 to Naphthalene Measurements in Indoor Air
Naphthalene has recently become a compound of concern in many vapor intrusion investigations as a result of its reclassification to a carcinogen by California EPA and its proposed change to a 'likely carcinogen' by the USEPA. Naphthalene is commonly found in petroleum-based fuels and may be present at former manufactured gas plants. To assess the health risk of naphthalene vapor migrating from fuel-contaminated sites into nearby buildings, measurements of naphthalene concentrations in the indoor air may be required. Due to the carcinogenic classification of naphthalene, the California human health screening levels (CHHSLs) for indoor air are in the sub-part per billion by volume (ppbv) range. Screening levels of 0.014 ppbv and 0.023 ppbv are listed for residential and commercial sites respectively1.
Several analytical approaches described in the EPA Compendium of Methods for the Determination of Toxic Organic Compounds in Ambient Air have been applied to air-phase naphthalene measurements. Two of the methods include Method TO-17. which uses a sorbent mbe for sample collection, and Method TO-15. which is a whole air canister sampling method. Method TO-15 is often the preferred approach for indoor air measurements due to the ease of sample collection and its applicability to a wide range of volatile organic compounds. However, the low vapor pressure of naphthalene and sub-ppbv screening levels raise questions as to the appropriateness of Method TO-15. With a vapor pressure of 0.089 Ton', naphthalene falls slightly below the 0.1 Ton* lower limit listed in the method. In addition, the reporting limits required to meet CHHSLs are more than one order of magnitude less than those described in Method TO-153. To apply Method TO-15 to naphthalene measurements in indoor air. careful evaluation of the collection and analytical procedures is necessary to insure defensible results are generated.