Breathing Zone Exposure Assessment - Aerosols: Measurement, Dosimetry, and Health Effects - page 37

Occupational compliance is rarely of concern, since carrying a BZ monitor periodically is usually
deined as a requirement of the job. Technologies are currently available to monitor wearing compli-
ance using activity sensors (e.g., Lawless, 2003). Laboratory tests with controlled movements of the
BZ sampler are used to set a threshold movement level below which the monitor can reasonably be
assumed to be stationary and not being worn. Rodes et al. (2010) found that approximately 50% of
the adult participants in a general population residential study wore the monitor less than 60% of the
protocol-deined sampling time. Two of the 35 participants wore the monitor less than 25% of the
time. For these participants, the levels of exposure misclassiication bias would be extremely large,
dependent upon the representativeness of the location where the monitors were left. Burden levels
(weight, inconvenience) are typically the largest contributing factors to poor compliance. Rodes
et al. (2010) reported similar results (1/3 of the participants wore the monitor <50% of the time)
for a 3 year, general population study in metro Detroit, MI. However, a comparable fraction of the
cohort was essentially fully compliant, suggesting that person-to-person wearing compliance, espe-
cially for general population cohorts is dificult to quantify without applying some level of wearing
compliance monitoring.
While it is dificult to extrapolate broadly from these data, the indings strongly suggest that
compliance can deinitely be an important factor in personal exposure studies. When the monitor
is not being worn as prescribed, it becomes a ixed-location monitor, resulting in data that are not
representative of personal exposures. Some likely locations for leaving the BZ monitors (e.g., on the
seat or in the trunk of a car) could seriously bias the contaminant levels, when only the monitor was
being exposed. In settings with strong point sources, the distinction between personal and ixed-
location monitors can be dramatically different. It is strongly recommended that efforts be made
in any BZ study where burden might be construed to be a compliance factor, to assess the degree
of compliance. While this may be as simple as asking follow-up questions, this approach may be
inadequate for some participants.

2.3 DEFINING THE BREATHING ZONE

2.3.1 r ationale
A relevant consideration here is the physiological deinition of the “breathing zone.” Occupational
exposure studies almost always require that the inlet be placed in the BZ to capture Bees but the
rationale and speciics for that recommendation are not always provided. Baron (2003) recom-
mended that personal exposure inlets sample air that would “most nearly represent that inhaled
by the employee” for occupational assessments. Fortunately, most participants in occupational
studies (a) are healthy adults, (b) are required to participate as part of the job, and (c) only need
to wear the monitor for 8 h periods. This simpliies the complexity design requirements for moni-
toring technologies applied from the perspective of the total burden (weight, size, obtrusiveness).
Nonoccupational studies, on the other hand, often include unhealthy, elderly adults and children,
utilize voluntary participants, and often require 24 h assessment periods. This places a premium on
the burden imposed on the study participants. Ideally, miniature passive badge samplers that can
unobtrusively be attached to the lapel are most effective. These have been developed for a number of
gases, and most recently efforts have been made to address aerosol collections passively (Brown and
Monteith, 2001; Wagner and Leith, 2001). The size and weight of active (pumped) sampling systems
for personal exposure pose substantial burden concerns for these classes of participants. The most
common locations for the inlets in or near the BZ are clipped to a coat, vest lapel, or shoulder strap,
or using a vest pocket.
Simplistically, the air parcel immediately in front of the nose and mouth from which the inhala-
tion volume is withdrawn might could be construed as the BZ. Deining the boundaries of this parcel
is not simple and varies with many factors including the inhalation/exhalation rate, microenviron-
mental air velocity and turbulence, nose versus mouth breathing, walking/running speed, etc. Often