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.