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Monitoring Options for Detection of Airborne Asbestos Dr. James Webber, Webber Environmental Health Consulting, LLC TASC Technical Advisor.

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Presentation on theme: "Monitoring Options for Detection of Airborne Asbestos Dr. James Webber, Webber Environmental Health Consulting, LLC TASC Technical Advisor."— Presentation transcript:

1 Monitoring Options for Detection of Airborne Asbestos Dr. James Webber, Webber Environmental Health Consulting, LLC TASC Technical Advisor

2 Monitoring Options for Detection of Airborne Asbestos Analytical Approaches Fiber Dimension Considerations Previous Asbestos Assessments at BoRit

3 Monitoring Options for Detection of Airborne Asbestos Analytical Approaches Real-time monitoring Phase contrast microscopy Scanning electron microscopy Transmission electron microscopy

4 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

5 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

6 Monitoring Options for Detection of Airborne Asbestos Microscopical analysis is based on collection on MCE filters

7 Monitoring Options for Detection of Airborne Asbestos Collapsed MCE filter

8 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

9 Monitoring Options for Detection of Airborne Asbestos

10 Disadvantages of PCM – Cannot identify asbestos False positives – Cannot detect fibers thinner than 0.25 µm False negatives

11 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

12 Monitoring Options for Detection of Airborne Asbestos

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14 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

15 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

16 Monitoring Options for Detection of Airborne Asbestos

17 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

18 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)

19 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

20 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

21 Monitoring Options for Detection of Airborne Asbestos Hypothesis: Longer fibers are more hazardous Stanton MF, et al Relation of particle dimension to carcinogenicity in amphibole asbestoses and other fibrous minerals J Natl Cancer Inst 67: The most “pathogenetically active” fibers are longer than 8 µm. Loomis et al Asbestos fiber dimensions and lung cancer mortality among workers exposed to chrysotile. Occup Environ Med 67: Long fibers are good predictors for lung cancer but not asbestosis.

22 Monitoring Options for Detection of Airborne Asbestos Hypothesis: Short fibers are hazardous Kane, A Fiber Dimensions and Mesothelioma: A Reappraisal of the Stanton Hypothesis. Mechanisms in Fibre Carcinogenesis. NATO ASI Series V. 223: “Both long and short crocidolite asbestos fibers are toxic.” Suzuki et al Short, thin asbestos fibers contribute to the development of human malignant mesothelioma: pathological evidence. Int. J Hyg. Environ. Health 208: “It is not prudent to take the position that short asbestos fibers convey little risk of disease.”

23 Monitoring Options for Detection of Airborne Asbestos Hypothesis: Thin fibers are most hazardous Stanton MF, et al Relation of particle dimension to carcinogenicity in amphibole asbestoses and other fibrous minerals. J Natl Cancer Inst 67: The most “pathogenetically active” fibers are thinner than 0.25 µm. Stayner et al An epidemiological study of the role of chrysotile asbestos fibre dimensions in determining respiratory disease risk in exposed workers. Occup Environ Med 65(9): “The thinnest fibres were the strongest predictor of lung cancer or asbestosis mortality in this study.”

24 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.”

25 Monitoring Options for Detection of Airborne Asbestos Previous Asbestos Assessments at BoRit – Limited to TEM analysis of air

26 Monitoring Options for Detection of Airborne Asbestos Phase 1 ambient air monitoring – Chrysotile was the only asbestos detected MethodDetection in 58 Samples Average Structures/cc ISO PCME ISO/PCME = 11

27 Monitoring Options for Detection of Airborne Asbestos Phase 2 ambient air monitoring – Chrysotile was the only asbestos detected MethodDetection in 98 Samples Average Structures/cc ISO PCME ISO/PCME = 22

28 Monitoring Options for Detection of Airborne Asbestos Phase 2 ABS air monitoring Chrysotile, amosite, crocidolite and actinolite were detected MethodDetected in 100 Samples Average Structures/cc ISO PCME ISO/PCME = 30

29 Monitoring Options for Detection of Airborne Asbestos Future Monitoring at BoRit It is unlikely that monitoring will be able to determine whether any detected contamination is from the Ambler Piles or from the BoRit site.

30 Monitoring Options for Detection of Airborne Asbestos Conclusions Real-time monitoring would be confusing False negatives False positives Not validated with microscopy Not recognized in the U.S.

31 Monitoring Options for Detection of Airborne Asbestos Conclusions TEM 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

32 Monitoring Options for Detection of Airborne Asbestos Turnaround Time Method12 Hour5 Day AHERA $60 - $90$35 - $70 ISO $175 - $400 $135 - $250 TEM Cost (per sample)

33 Monitoring Options for Detection of Airborne Asbestos Questions?


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