INVESTIGATION OF DUST MIGRATION CAUSED FROM THE TRANSPORTATION OF SAMPLES
Abstract No:
1715
Abstract Type:
Student Poster
Authors:
G Erekaife1, E Lee2
Institutions:
1West Virginia University, Morgantown, WV, 2NIOSH, Morgantown, WV
Presenter:
Mr Godwin Erekaife
West Virginia University
West Virginia University
Faculty Advisor:
Dr Eun Gyung (Emily) Lee
NIOSH
NIOSH
Description:
Aerosol samples collected from occupational environments are often transported to a laboratory for gravimetric analysis by placing covers on the samplers or placing filters in filter containers. Depending on the sampling media and sampler type, either filter (e.g. closed-face cassette [CFC]) or capsule (e.g. Accu-CAP™) can be weighed. However, the amount of dust migrated to the cover of sampler or the surface of filter container is not accounted for during the gravimetric analysis. One exception is the IOM sampler, where users can measure the whole capsule with its cover. The present study investigated an effect of dust migration caused from the transportation of samples collected for gravimetric analysis. Wood dust was generated in an environmentally controlled chamber and collected with four samplers: 37-mm CFC, 37-mm Accu-CAP, 25-mm disposable inhalable sampler, and 25-mm IOM sampler. The samples were divided into two groups, each transported by air or land, and the returned samples were analyzed gravimetrically.
Results indicate that the mode of transportation has a significant effect on the amount of dust migrated to the cover of samplers and the magnitude of migration varies depending on the sampler type. This study suggests that modest but important adjustments should be considered for occupational professionals when handling and analyzing wood dust samples in practice.
Results indicate that the mode of transportation has a significant effect on the amount of dust migrated to the cover of samplers and the magnitude of migration varies depending on the sampler type. This study suggests that modest but important adjustments should be considered for occupational professionals when handling and analyzing wood dust samples in practice.
Situation/Problem:
Prior investigations of aerosol sampling have addressed high proportions of particle deposition on the interior walls of samplers during sampling and/or transporting of samples. For example, Puskar et al. (1991) found that only 22% of the active ingredient of the pharmaceutical dust sampled settled on the filters, with 78% depositing elsewhere. Mark (1990) reported significant amounts of the sampled aerosol deposited to the samplers' internal walls ranging from 5% to 50%. As a result, several measures have been enacted to accommodate these concerns. The Occupational Safety and Health Administration currently requires that sampler cassettes be wiped thoroughly to include even invisible particles not collected on the filters when evaluating metals (Hendricks et al. 2009). The National Institute for Occupational Safety and Health (NIOSH) also recommends wiping of internal walls for metal analysis in their Manual of Analytical Methods (5th Edition, Chapter AE) and in published methods (e.g. NIOSH 7302 and 7303).
However, little attention has been given to particles that could settle on the sampler covers during the sample transportation. This migration, if not adequately accounted for, would create the same concerns (i.e. underestimation) as do unaccounted particles on internal sampler surfaces. Thus, the purpose of this study is to investigate the effect of dust migration caused during the transportation of samples.
However, little attention has been given to particles that could settle on the sampler covers during the sample transportation. This migration, if not adequately accounted for, would create the same concerns (i.e. underestimation) as do unaccounted particles on internal sampler surfaces. Thus, the purpose of this study is to investigate the effect of dust migration caused during the transportation of samples.
Methods:
Birch wood dust was collected in an environmentally controlled chamber, where a sander equipped with a P120-grit sandpaper to perform sanding of a wooden log. Four types of inhalable or total dust samplers were used: 37-mm closed-face cassette (CFC; SKC Inc.), 37-mm Accu-CAP™ (SKC Inc.), 25-mm disposable inhalable sampler (DIS; Zefon International), and 25-mm IOM sampler (SKC Inc.), with each sampler loaded with a polyvinylchloride (PVC) filter with 5 µm pore size. All samplers were run at a nominal flowrate of 2 LPM. Sampling flowrates before and after sampling were checked with a mass flowmeter to ensure the flowrate was within ± 5% of the nominal flowrate. We generated four mass levels of wood dust (0.5, 1, 2, and 3.5 mg) based on the ranges of filter loadings recommended by NIOSH 0500 and 0501 methods. For each sampler type, a total of 32 samples were collected.
Prior to the sample collection, PVC filters for CFC and IOM samplers and internal capsules for Accu-CAP and DIS samplers were equilibrated in an environmentally controlled weighing room (temperature at 26 ± 2°C and relative humidity of 50 ± 2 %) for 48 hours. Pre-weights were then taken using a microbalance with a 0.00001 mg sensitivity. In addition, pre- weights were recorded for the covers of samplers to determine the dust migration to the sampler cover during transportation. Six blank samples were prepared for each sampler using the same procedure.
After sampling, all 128 samples (32 samples/sampler type x 4 masses) were divided into 2 groups, along with the blank samples for air and land transport. For the first group, the sample box was shipped to Florida, USA and returned by a priority overnight commercial airfreight. An approximation of the chain of custody is as follows: the courier service picked up the box from Morgantown, WV, drove it to an airport where the box was flown approximately 900 miles to its destination and driven to the receiving facility, which returned the box in the same manner. For the second group, the sample box was driven in a personal vehicle, and thus the conditions of its transit were more controlled. It was driven to its destination 300 miles away and returned in the same manner for a total of 600 miles round-trip. The terrain was mostly interstate paved road with mild turns and an easy gradient resulting in about 800 feet difference in elevation between the departure and destination.
After transportation, the samples were set to equilibrate in the weighing room for 48 hours and post-weights for the sampling media and sampler covers were taken with the same microbalance used for the pre-weights. In order to minimize the variation by different analysts, the same person conducted both the pre- and post-weights.
Prior to the sample collection, PVC filters for CFC and IOM samplers and internal capsules for Accu-CAP and DIS samplers were equilibrated in an environmentally controlled weighing room (temperature at 26 ± 2°C and relative humidity of 50 ± 2 %) for 48 hours. Pre-weights were then taken using a microbalance with a 0.00001 mg sensitivity. In addition, pre- weights were recorded for the covers of samplers to determine the dust migration to the sampler cover during transportation. Six blank samples were prepared for each sampler using the same procedure.
After sampling, all 128 samples (32 samples/sampler type x 4 masses) were divided into 2 groups, along with the blank samples for air and land transport. For the first group, the sample box was shipped to Florida, USA and returned by a priority overnight commercial airfreight. An approximation of the chain of custody is as follows: the courier service picked up the box from Morgantown, WV, drove it to an airport where the box was flown approximately 900 miles to its destination and driven to the receiving facility, which returned the box in the same manner. For the second group, the sample box was driven in a personal vehicle, and thus the conditions of its transit were more controlled. It was driven to its destination 300 miles away and returned in the same manner for a total of 600 miles round-trip. The terrain was mostly interstate paved road with mild turns and an easy gradient resulting in about 800 feet difference in elevation between the departure and destination.
After transportation, the samples were set to equilibrate in the weighing room for 48 hours and post-weights for the sampling media and sampler covers were taken with the same microbalance used for the pre-weights. In order to minimize the variation by different analysts, the same person conducted both the pre- and post-weights.
Results / Conclusions:
Although we intended to investigate the effect of dust migration by mass level, due to the spatial variation of masses at each level, the results presented here are based on the combined data. The median mass (standard deviation [SD]) for the CFC, Accu-CAP, DIS, and IOM was 0.7 mg (SD=1.1), 0.6 mg (SD=2.6), 1.5 mg (SD=0.7), and 3.8 mg (SD=4.2), respectively, for the land transported samples and 0.4 mg (SD=0.9), 0.9 mg (SD=0.8), 1.5 mg (SD=0.7), and 1.0 mg (SD=2.0), respectively, for the air transported samples. Note that the mass reports the dust collected on the sampling media and the covers of all samples.
The percentage of dust migrated to the covers during the land transportation ranged from 0 to 3.5% (median=1.0%), 1.1 to 36% (median=9.4%), 0 to 31% (median=12%), and 0.2 to 87% (median=33%) for the CFC, Accu-CAP, DIS, and IOM, respectively. Similarly, for the air transportation, percentages ranged from 2.5 to 62 % (median=10%), 0 to 80% (median=6.5%), 0 to 16% (median=1.3%), and 10 to 93% (median=63%) for the CFC, Accu-CAP, DIS, and IOM, respectively.
Statistically significant differences were observed for the IOM and CFC samplers when comparing the proportion of dust migrated to the sampler covers between the air and land transport, while no differences were observed for the others. When the comparison was made among different sampler types, regardless of the mode of transportation, only the IOM samplers showed a significant difference compared to the others.
The findings of this study demonstrated that the mode of transportation for wood dust samples affects its subsequent weighing analysis, and the magnitude of dust migration varies depending on the type of samplers. Special caution should be given to samplers having wide inlet diameter (e.g. IOM) due to its greater vulnerability to particles bouncing to the sampler covers. For example, the IOM sampler having wider opening area showed considerably higher percentage of dust migrated to the cover compared to others. It is noteworthy that this phenomenon was not observed in the DIS sampler even though it shares a similar inlet diameter with the IOM sampler. The difference might be caused from the non-conductive plastic body of the DIS sampler that restricts the particle migration, making it more likely to stick to its capsule. The manufacturer of the IOM sampler suggests weighing of the sampler cover as an option. However, we strongly suggest that practitioners include the cover in the weighing analysis to prevent potential loss of dust from the sample transportation.
One limitation of this study is our inability to predict the precise nature of material handling of the shipment box during the transportation of the samples. Thus, the proportion of dust migrated to the covers reported in this study might be subjective and could be different depending on the conditions of sample handling (e.g. road condition, handlers' characteristics, travelling distance).
The percentage of dust migrated to the covers during the land transportation ranged from 0 to 3.5% (median=1.0%), 1.1 to 36% (median=9.4%), 0 to 31% (median=12%), and 0.2 to 87% (median=33%) for the CFC, Accu-CAP, DIS, and IOM, respectively. Similarly, for the air transportation, percentages ranged from 2.5 to 62 % (median=10%), 0 to 80% (median=6.5%), 0 to 16% (median=1.3%), and 10 to 93% (median=63%) for the CFC, Accu-CAP, DIS, and IOM, respectively.
Statistically significant differences were observed for the IOM and CFC samplers when comparing the proportion of dust migrated to the sampler covers between the air and land transport, while no differences were observed for the others. When the comparison was made among different sampler types, regardless of the mode of transportation, only the IOM samplers showed a significant difference compared to the others.
The findings of this study demonstrated that the mode of transportation for wood dust samples affects its subsequent weighing analysis, and the magnitude of dust migration varies depending on the type of samplers. Special caution should be given to samplers having wide inlet diameter (e.g. IOM) due to its greater vulnerability to particles bouncing to the sampler covers. For example, the IOM sampler having wider opening area showed considerably higher percentage of dust migrated to the cover compared to others. It is noteworthy that this phenomenon was not observed in the DIS sampler even though it shares a similar inlet diameter with the IOM sampler. The difference might be caused from the non-conductive plastic body of the DIS sampler that restricts the particle migration, making it more likely to stick to its capsule. The manufacturer of the IOM sampler suggests weighing of the sampler cover as an option. However, we strongly suggest that practitioners include the cover in the weighing analysis to prevent potential loss of dust from the sample transportation.
One limitation of this study is our inability to predict the precise nature of material handling of the shipment box during the transportation of the samples. Thus, the proportion of dust migrated to the covers reported in this study might be subjective and could be different depending on the conditions of sample handling (e.g. road condition, handlers' characteristics, travelling distance).
Primary Topic:
Aerosols
Secondary Topics:
Exposure Assessment Strategies
Sampling and Analysis
Co-Authors
Please add your co-authors below. Co-authors are listed for professional courtesy and will not be communicated with regarding the decision notification or any on-site logistics, if accepted. Only the primary presenter listed is expected to attend and present the content on-site.
Eun Gyung Lee: Physical Research Scientist, National Institute for Occupational Safety and Health (NIOSH), Health Effects Laboratory Division (HELD), Exposure Assessment Branch
Michael L. Kashon: Statistician, National Institute for Occupational Safety and Health (NIOSH), Health Effects Laboratory Division (HELD), Bioanalytics Branch
Acknowledgements and References
List any additional people who worked on the project or provided guidance and support along with details on the role they played in the research. (Please include first name, last name, organization, city, state and country).
Practical Application
How will this help advance the science of IH/OH?
Special caution should be given to samplers having wide inlet diameter (e.g. IOM) due to its greater vulnerability to particles bouncing to the sampler covers. For example, the IOM sampler having wider opening area showed considerably higher percentage of dust migrated to the cover compared to the other samplers used in the study although it is noteworthy that this phenomenon was not observed in the DIS sampler even though it shares a similar inlet diameter with the IOM sampler. The difference might be caused from the non-conductive plastic body of the DIS sampler that restricts the particle migration, making it more likely to stick to its capsule.
The manufacturer of the IOM sampler suggests weighing of the sampler cover as an option. However, we strongly suggest that practitioners include the cover in the weighing analysis to prevent potential loss of dust from the sample transportation.