Monitoring Options for Detection of Airborne Asbestos Dr. James Webber, Webber Environmental Health...

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


Analytical ApproachesReal-time monitoringPhase contrast microscopyScanning electron microscopyTransmission electron microscopy


• 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


• 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


• Microscopical analysis is based on collection on MCE filters


• Collapsed MCE filter


• 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


• Disadvantages of PCM– Cannot identify asbestos

• False positives

– Cannot detect fibers thinner than 0.25 µm• False negatives


• 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


• 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


• 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


• 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


• 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)


• 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


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.


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.”


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.”

http://www.ncbi.nlm.nih.gov/pubmed/18096653


Stanton Hypothesis (1981)

The most “pathogenetically active” fibers:Longer than 8 µmThinner 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.”


• Previous Asbestos Assessments at BoRit– Limited to TEM analysis of air


• 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


• Phase 2 ambient air monitoring – Chrysotile was the only asbestos detected

Method Detection in 98 Samples


ISO 17 0.00061

PCME 3 0.000028

ISO/PCME = 22


• Phase 2 ABS air monitoring • Chrysotile, amosite, crocidolite and actinolite were detected

Method Detected in 100 Samples


ISO 82 0.76

PCME 59 0.025

ISO/PCME = 30


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.


ConclusionsReal-time monitoring would be confusing

False negativesFalse positivesNot validated with microscopyNot recognized in the U.S.


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


Turnaround TimeMethod 12 Hour5 Day

AHERA $60 - $90 $35 - $70

ISO $175 - $400 $135 - $250

TEM Cost (per sample)


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Monitoring Options for Detection of Airborne Asbestos Dr. James Webber, Webber Environmental Health...

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