1 / 35

The value of microscopy analysis Garry Burdett Health and Safety Laboratory Harpur Hill, Buxton, UK, SK17 9JN

thora
Download Presentation

The value of microscopy analysis Garry Burdett Health and Safety Laboratory Harpur Hill, Buxton, UK, SK17 9JN

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

    1. The value of microscopy analysis Garry Burdett Health and Safety Laboratory Harpur Hill, Buxton, UK, SK17 9JN

    2. Asbestos Hazard Mortality (excess deaths) due to: Fibrosis of the lung (asbestosis) Cancer of the lung (bronchial cancer etc) Cancer of the lung lining (e.g. mesothelioma) Morbidity (lung changes/dysfunction) Pleural plaques; Diffuse pleural effusions

    3. Fibre Related Risk: Depends on: Dimensions Durability / Type Dose / Exposure Time (Measurable by microscopy)

    4. EU Directive: Dimensions For the purposes of measuring in the air, only fibres with a length of more than five micrometres, a breadth of less than three micrometres and a length to breadth ratio greater than 3:1 shall be taken into consideration. (2003/18/EC amending to EU asbestos worker protection directive (83/477/EEC) article 7.6 )

    5. Durability / Type

    6. Dose / Exposure Exposure is used as a surrogate for dose by sampling a known volume of air onto a membrane filter and counting the numbers of fibres present in a known area. This is used to calculate the fibre concentration in f/ml or f/cm3 of air. Uses size criteria to determine ability to reach pulmonary region of the lung.

    7. Time Dose = exposure x duration (f/ml/years) Risk µ cumulative dose (assume linear); Risk µ time since first exposure (mesothelioma related by power law). Lag time 15 – 60 years from exposure to disease symptoms

    8. EU directive: Fibre Counting “Fibre counting shall be carried out whenever possible by PCM (Phase contrast microscope) in accordance with the 1997 (World Health Organisation) recommended method (16) or any other method giving equivalent results.”

    9. EU Directive: Requirements The 2003 amendment to 83/477/EEC abandoned action levels and different control levels for different types of asbestos and introduced a single limit of 0.1 f/ml over an 8-hour time weighted average. (Article 8) Therefore the EU regulation for controlling the risk to workers, require only PCM fibre number information over a broadly defined size range. Article 4 requires the type and quantities of asbestos handled to be notified

    10. Main types of microscopy for fibre counting. Phase contrast light microscopy PCM Scanning electron microscopy SEM Transmission electron microscopy TEM. All have ISO or WHO standard methods Polarised light microscopy PLM for bulk analysis.

    12. PCM (X500 magnification)

    13. SEM

    14. TEM

    15. SEM higher Mag & 3D

    16. TEM high mag chrystotile

    17. PLM : Dispersion staining

    18. Discrimination of fibre type PCM: No discrimination or identification ; PLM Uses optical properties + refractive index/ dispersion colours to identify fibres; >0.8µm width; SEM uses Energy Dispersive X-ray analysis to semi-quantitatively measure chemistry; TEM uses quantitative EDX and electron diffraction to identify fibres.

    20. Comparison of methods for fibre counting

    21. Likely upper limit of detection (f/ml) by method and volume

    22. Accuracy & Precision Accuracy not usually known. Precision includes: Random “Poisson” counting error Instrumental errors (QA / calibration) Human errors (QA / Proficiency testing)

    23. Random counting errors (95%)

    24. Quality and accreditation Quality assurance and proficiency testing is essential, particularly if results from different analysts and laboratories are being used or compared. Accreditation of Laboratories to ISO 17025 mandated by the EU directive.

    26. RICE: Fibre counting PT RICE - 187 labs. MMMF – 12 labs. ERM – WHO major change

    27. AIMS: Fibre Identification PT

    28. Value of PCM counting Workplace exposure can be controlled using the WHO - PCM method; Counts “regulated” WHO fibres & meets EU criteria; Relatively quick (on-site) and cheap; Environmental exposure can be screened by PCM.

    29. PCM Limitations PCM has limited detection due to background counts on blank filters (0.01 f/ml); No knowledge of fibre types; Only an “index of exposure”

    30. Value of analytical SEM Can be adjusted to give regulated fibre counts, Can give fibre size information, Classifies fibre types present using EDX spectra data.

    31. SEM limitations Limited availability; Off site analysis; Costly Can only be used for regulated fibre counting, No definitive identification of fibres, Lowest area of filter scanned per field of view.

    32. Value of TEM Can count regulated fibres + all fibre sizes. Accurate size information, EDX chemical analysis of all fibre sizes Crystal structure information (SAED) Identification of fibre type, Can give complete information on all fibre sizes if needed

    33. Limitations of TEM Limited availability; Off site; Costly

    34. Recommendations 1 Use PCM for workplace control and checking after clean –up (with disturbance sampling). Indoor and near source environmental use PCM screening and SEM or TEM analysis (as necessary) on selected half-filters. Ambient air: Analytical TEM is best, SEM is more limited, PCM not very useful.

    35. Recommendations 2 Use Polarised light microscopy (PLM) for analysis of bulk samples for asbestos present and type of asbestos. Use PLM to screen minerals and soils for asbestos content. Asbestos in water usually analysed by TEM

More Related