Abstract
Stir bar sorptive extraction (SBSE) was compared with standardized pump sampling regarding the prospects to assess airborne levels of polycyclic aromatic hydrocarbons (PAHs) in indoor environments. A historic railway water tower, which will be preserved a technical monument for museum purposes, was sampled with both approaches because built-in insulation material was suspected to release PAHs to the indoor air. The 16 PAH on the US EPA list were quantified using gas chromatography with mass selection detection in filters from pump sampling after solvent extraction and on SBSE devices after thermal desorption. SBSE was seen to sample detectable PAH masses with excellent repeatability and a congener pattern largely similar to that observed with pump sampling. Congener patterns were however significantly different from that in the PAH source because release from the insulation material is largely triggered by the respective congener vapor pressures. Absolute masses in the ng range sampled by SBSE corresponded to airborne concentrations in the ng L-1 range determined by pump sampling. Principle differences between SBSE and pump sampling as well as prospects of SBSE as cost-effective and versatile complement of pump sampling are discussed.
Keywords: PAH, adsorption, sampling, stir bar, extraction, GC-MS
Correspondence to: Roland Becker
roland.becker@bam.de
Introduction
The permissible concentration of harmful substances such as polycyclic aromatic hydrocarbons (PAH) in indoor air is regulated1,2. Obvious sources for such compounds are normally tackled by insulation, a ventilation regime or are removed altogether. In the context of displaying industrial heritage to the public in a museum setting there is reason to retain technical installations in their original form. This can lead to contaminant sources that require careful handling in compliance with the regulation in place. In the concrete case a water tower constructed in 1904 near Berlin, Germany, and operated until 1987 for boiler feedwater supply for steam trains is being conserved in the found condition as industrial monument with the aim to admit visitors. During operation of the tower water was pumped through steel pipes from a well under the tower into the reservoir above the third floor. Pipelines and fittings were insulated with jute fabric and cardboard soaked with a bituminous material. Consequently, the insulation material contains PAH in considerable amounts which leads inevitably to the release of PAH to the indoor air. Therefore, the PAH concentration in the air is relevant to manage the admission of museum visitors. Indoor concentrations of naphthalene and benzo[a ]pyrene are regulated and should not exceed 10 mg m-3 and 1 ng m-3, respectively1,2. A number of procedural variants most based on pump sampling for the determination of airborne PAH levels have been reported3. Usually, concentration levels are determined following the pump sampling procedure laid down in ISO 16000-124.
No visitors other than technical staff were admitted to the water tower during the restoration period. The third floor below the water reservoir tank, which is called “Tropfboden” (literally: “drip floor”, due to dripping of condensed moisture), was chosen as a point of central museum interest, because of the tank and its special distribution of pipelines. According to the safety habits of the time of construction, the drip floor is accessed via an exceptionally steep, long steel ladder. As a result, the transport of the pump sampling equipment was impeded. This situation was used to explore a rapid and easily applicable passive sampling approach regarding its proficiency as a complement to pump sampling. A straight-forward option for facile sampling is stir bar sportive extraction (SBSE) that is based on exposure of coated magnetic bars to environmental compartments and has been used over than 20 years for a variety of analytes5. While the focus has been on extraction from aqueous phases stir bar extraction from open air has been reported for phosphorous flame retardants6 and as headspace SBSE for determination of volatiles form food7,8 and in forensic applications9,10. Regarding PAH so far nearly exclusively application of SBSE for trace concentration determinations in water has been reported11,12,13,14,15,16,17,18. Meanwhile, the use SBSE for the assessing the effect of coal combustion on indoor airborne PAH levels was reported19. SBSE displays straight forward and easy application as devices may be exposed for different periods of time, easily transported after collection, stored over prolonged periods of time and analysed under repeatability conditions. Thus, a proof of concept study was performed to explore SBSE as tool to provide a rapid estimate of PAH concentration levels in order to assess the significance for more complex standardized sampling procedures.