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Monitoring Options for Detection of Airborne Asbestos. Dr. James Webber, Webber Environmental Health Consulting, LLC TASC Technical Advisor. Monitoring Options for Detection of Airborne Asbestos. Analytical Approaches. Fiber Dimension Considerations. - PowerPoint PPT Presentation
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Monitoring Options for
Detection of Airborne Asbestos
Dr. James Webber, Webber Environmental Health Consulting, LLC
TASC Technical Advisor
Monitoring Options for Detection of Airborne Asbestos
Analytical Approaches
Fiber Dimension Considerations
Previous Asbestos Assessments
at BoRit
Monitoring Options for Detection of Airborne Asbestos
Analytical ApproachesReal-time monitoringPhase contrast microscopyScanning electron microscopyTransmission electron microscopy
Monitoring Options for Detection of Airborne Asbestos
• Real-time monitoring– Patent application in 1988– Air passes through a column where
fibers are aligned to pass through a laser– A particle’s scattered light is collected by
a detector, which determines fibrosity– Counts are accumulated to determine
concentration
Monitoring Options for Detection of Airborne Asbestos
• Shortcomings of real-time monitoring– Cannot identify asbestos
• Numerous non-asbestos fibers• False positives
– Cannot detect thin fibers• False negatives
– No published evidence of comparison to accepted microscopical methods
– Not recognized by federal agencies
Monitoring Options for Detection of Airborne Asbestos
• Microscopical analysis is based on collection on MCE filters
Monitoring Options for Detection of Airborne Asbestos
• Collapsed MCE filter
Monitoring Options for Detection of Airborne Asbestos
• Phase contrast light microscopy (PCM)– Used for occupational monitoring since 1960s– Analyze filter at 400x magnification– Count as fibers:
• >5 µm• Aspect ratio (length/width) >3
Monitoring Options for Detection of Airborne Asbestos
Monitoring Options for Detection of Airborne Asbestos
• Disadvantages of PCM– Cannot identify asbestos
• False positives– Cannot detect fibers thinner than 0.25 µm
• False negatives
Monitoring Options for Detection of Airborne Asbestos
• Scanning electron microscopy (SEM)– 30 keV beam allows resolution of fibers
thinner than detected by PCM– Energy-dispersive X-ray analyzer (EDX)
yields chemical composition of fiber
Monitoring Options for Detection of Airborne Asbestos
Monitoring Options for Detection of Airborne Asbestos
Monitoring Options for Detection of Airborne Asbestos
• Disadvantages of SEM– Inconsistent resolution of thin fibers
• Instrumental variations• Viewing surface of fiber
– No determination of crystalline structure
– Not recognized in the U.S. for monitoring
Monitoring Options for Detection of Airborne Asbestos
• Transmission electron microscopy (TEM)– 80+ keV electron beam resolves thinnest
fibers– EDX yields chemical composition– Selected-area electron diffraction
characterizes crystalline structure• Recognized by federal agencies• About 75 accredited TEM laboratories
Monitoring Options for Detection of Airborne Asbestos
Monitoring Options for Detection of Airborne Asbestos
• TEM analysis methods– ISO
• Measures dimensions of all asbestos fibers– AHERA
• Divides asbestos fibers into:– >0.5 µm and <5 µm, or– >5 µm
– PCME• Counts only asbestos fibers longer than 5 µm, wider
than 0.25 µm, and aspect ratios >3– BC
• Counts only fibers longer than 10 µm and thinner than 0.4 µm
Monitoring Options for Detection of Airborne Asbestos
• Fiber Dimensions– Fiber dimensions are parameters that are
considered during asbestos risk assessment
– Risk assessment is beyond the scope of this report
– Nonetheless, fiber dimensions will be briefly reviewed because of their impact on analytical approach (ISO/AHERA/PCME/BC)
Monitoring Options for Detection of Airborne Asbestos
• Asbestos fibers with a diameter of less than 0.5 µm can reach the deep lungs
• The mineral durability of asbestos fibers keeps them from being dissolved in the lungs
• Risk-analysis conundrum• Largest database of asbestos diseases is from
workers exposed before the 1970s– High airborne concentrations– Decades-long latency period
• Measurements of their exposures were by PCM• TEM became available around the mid-1970s,
after exposures were greatly reduced• Therefore, very little information exists on fiber
dimensions that caused observed asbestos diseases in humans
Monitoring Options for Detection of Airborne Asbestos
Hypothesis: Longer fibers are more hazardous
Stanton MF, et al. 1981. Relation of particle dimension to carcinogenicity in amphibole asbestoses and other fibrous minerals J Natl Cancer Inst 67:965-975.The most “pathogenetically active” fibers are longer than 8 µm.
Loomis et al. 2010. Asbestos fiber dimensions and lung cancer mortality among workers exposed to chrysotile. Occup Environ Med 67:580-584. Long fibers are good predictors for lung cancer but not asbestosis.
Monitoring Options for Detection of Airborne Asbestos
Hypothesis: Short fibers are hazardous
Kane, A. 1991. Fiber Dimensions and Mesothelioma: A Reappraisal of the Stanton Hypothesis. Mechanisms in Fibre Carcinogenesis. NATO ASI Series V. 223: 131-141.“Both long and short crocidolite asbestos fibers are toxic.”
Suzuki et al. 2005. Short, thin asbestos fibers contribute to the development of human malignant mesothelioma: pathological evidence. Int. J Hyg. Environ. Health 208:439-44.“It is not prudent to take the position that short asbestos fibers convey little risk of disease.”
Monitoring Options for Detection of Airborne Asbestos
Hypothesis: Thin fibers are most hazardous
Stanton MF, et al. 1981. Relation of particle dimension to carcinogenicity in amphibole asbestoses and other fibrous minerals. J Natl Cancer Inst 67:965-975.The most “pathogenetically active” fibers are thinner than 0.25 µm.
Stayner et al. 2008. An epidemiological study of the role of chrysotile asbestos fibre dimensions in determining respiratory disease risk in exposed workers. Occup Environ Med 65(9):613-9. “The thinnest fibres were the strongest predictor of lung cancer or asbestosis mortality in this study.”
Monitoring Options for Detection of Airborne Asbestos
Stanton Hypothesis (1981)
The most “pathogenetically active” fibers:Longer than 8 µm
Thinner than 0.25 µm
“….but relatively high correlations were also noted with fibers in other size categories having diameters up to 1.5 micrometer and lengths greater than 4 micrometer.”
Monitoring Options for Detection of Airborne Asbestos
• Previous Asbestos Assessments at BoRit– Limited to TEM analysis of air
Monitoring Options for Detection of Airborne Asbestos
• Phase 1 ambient air monitoring – Chrysotile was the only asbestos detected
Method Detection in 58 Samples
AverageStructures/cc
ISO 4 0.00018
PCME 1 0.000017
ISO/PCME = 11
Monitoring Options for Detection of Airborne Asbestos
• Phase 2 ambient air monitoring – Chrysotile was the only asbestos detected
Method Detection in 98 Samples
AverageStructures/cc
ISO 17 0.00061
PCME 3 0.000028
ISO/PCME = 22
Monitoring Options for Detection of Airborne Asbestos
• Phase 2 ABS air monitoring • Chrysotile, amosite, crocidolite and actinolite were detected
Method Detected in 100 Samples
AverageStructures/cc
ISO 82 0.76
PCME 59 0.025
ISO/PCME = 30
Monitoring Options for Detection of Airborne Asbestos
Future Monitoring at BoRitIt is unlikely that monitoring will be able to determine whether any detected contamination is from the Ambler Piles or from the BoRit site.
Monitoring Options for Detection of Airborne Asbestos
ConclusionsReal-time monitoring would be confusing
False negativesFalse positivesNot validated with microscopyNot recognized in the U.S.
Monitoring Options for Detection of Airborne Asbestos
ConclusionsTEM would be the method of choice
Detects and identifies all asbestos fibers
Allows measurement of fiber dimensions
Methods recognized by federal regulators
Many accredited TEM laboratories
Monitoring Options for Detection of Airborne Asbestos
Turnaround TimeMethod 12 Hour 5 Day
AHERA $60 - $90 $35 - $70
ISO $175 - $400 $135 - $250
TEM Cost (per sample)
Monitoring Options for Detection of Airborne Asbestos
Questions?