Microscan Assessments of Find Particulate Matter Samples

Posted by on December 15, 2021

GENERIC INFORMATION PERTAINING TO MICROSCAN ASSESSMENTS OF FINE PARTICULATE MATTER SAMPLES

  • ILLUSTRATION OF METHODOLOGY PROCEDURES, DESIGNED TO ENSURE CONSISTENCY AND ACCURACY.

Microscan Assessments of Find Particulate Matter Samples

Image 1: The microscope currently being used.  UB100i Biological Binocular – 4 eye magnifications. UOP. SKU: SW-70051-BS-UB100i.  See specifications in Appendix A.

  • Introduction
    MicroScans are merely a description of accepted geological and other procedures for the recognition of rock fine material and other airborne material, distributed through-out a captured sample.
    While there are many more accurate quantitative analytical procedures, almost all are extremely expensive and all have limitations as they are designed for one purpose without considering other tests that may need to be done on the sample.
    It is important to interpret the results from such quantitative tests with the assistance of the background knowledge of how the sample was taken and site specific information.
    Often laboratory reports are only of academic value and do not bring new information to the table to assist in interpreting the results. The basics of any analysis is that it must provide additional information that is useful for the interpretation of the data being discussed.
    Spectrographic analysis is fine for the various mineral elements or individually for various compounds and element combinations, but all of the organic matter has to be either ashed or acid digested, and thus unless you have done a huge bulk sample capture, you will use up all of the sample to arrive at the elemental content.
    You will then need more material to be able to look at the organic chemistry type contents and yet a third sample to be able to look at the biological content and so on.
    Again, while not the perfect solution, the MicroScan is an intelligent scrutiny of samples that does not destroy or contaminate the sample.
  • Accuracy and Application

Things of concern in establishing the accuracy of any analytical method, as with field and laboratory geology, the initial recognition of a sample will rely on the colour of the sample, the hardness, form of the material in its normal state, and its propensity to break along fracture planes.  The fact that there is a list of geological materials falling into various hardness categories, which are used to establish how hard the material is, with harder material always damaging material of a softer hardness.
Other features of geology of use are the lustre presented on broken surfaces, and the crystalline structure of most minerals.
No matter how small the particulate may be, this will, in most cases, still display its crystalline form.  The hardness of each will then predict how fine dust material will wear, especially when driven over on roadways, quarries, and on dumps.  As dirt can be exceedingly small, this is the scale we need to work at and thus it is imperative that samples can be viewed at anything from scores, hundreds or even thousands of magnifications.  The advent of the digital imaging and various light sources, permits us not only to make observations but to photograph the noted features and specimens present.
The existence of a microscopic world out there also offers an opportunity to find microscopic life forms, or sub-micronic material and the larger more common pollen spores, algae, bacteria, and moulds which can influence health.  These potential health impacts are a concern and do impact on the health of people exposed to them.
Silicosis is caused by fine silica dust, and anthracosis is caused by fine coal dust.  Other forms of respirable disease are caused by other fine dusts, and the MicroScans enable the identification of fibres as well as fine organic material that can have a health impact.
It is a great big “tiny world” out there and there is no reason to only consider the mass of fine particulate matter, PM2.5 or PM10 or even PM30, but why not look for fibres which are present in airborne dusts, spores, moulds and other material which all have largely been ignored with regarding to their impacts on health.
The fact that collection methods only consider a material that remains after ashing or digestion also misses the golden opportunity of seeing what inaccuracies occur in many of the well-established and accepted methodologies.
The MicroScan technician in this case has to have a skill set and the skill base we work from is the knowledge of geology, occupational hygiene, organic chemistry and finally biology.  There are also some elements of forensics.

  • Sample Preparation

Ideally samples should be in a standard, 47mm petri slides with a tight fitted lid.  This allows the sample to be easily sealed when not being MicroScanned.
FFP1 or FFP2 respirators can be used to prevent the inhalation of fine respirable particulates.
Gloves should not be worn, as the combination of fabrics could cause static and the possible loss of fine material.
Forceps must be used to handle any samples.

  • Observations, Digitised Images and Preparation of Report photographs

The samples are scanned, and a representative image selected.  All size fractions are determined using a graticule.  The graticule size starts at 10 Micron and allows for the d50 diameter of a samples to be estimated.
The image is selected for photography if required.  Should there be any features or unusual material in the sample or a biological specimen, then this can be photographed, either in addition to or instead of the predominant particulate on the filter paper.
The photograph can be taken at four magnifications depending on the requirements.
1:400

1:4000
1:1000
1:10000

The Microscope has four magnification (mag) settings, 4x, 10x, 40x, and 100x as a field lens.  The eye piece increases the magnification by 10x, and the camera increases it by 100 times.  The camera is fitted to the top of the microscope and the eye piece magnification is not included.

The total length of the gratical in the image below is 1mm from end to end.  Each small line indicates a gap of 10 micron, each medium line is a gap of 50 micron and each long line is a gap of 100 micron.

Image 2:  The above image photographed at a magnification of 4x field lens and 100x optical camera image, totalling 400 magnifications.

Image 3  The above image photographed at a magnification of 10x field lens and 100x optical camera image, totalling 1000 magnifications.

Image 4:  The above image photographed at a mag of 40x field lens and 100x optical camera image, totalling 4000 magnifications.

Image 5:  The above image photographed at a mag of 100x field lens and 100x optical camera image, totalling 10000 mags.
In practise this magnification cannot be achieved as the LED light source is not good enough to illuminate through the clear glass graticule, as can be noted by the image.

Note that the scaling is only applicable if the original image from the microscope is viewed at 100% size, and if the image has not been digitally resized.  The images above have been digitally resized.

There are some unknowns when doing MicroScans as described above and this should be considered when interpreting the results.

MicroScan assessments are a collection of recognised Geological and structural techniques utilised at microscopic level to determine the gross contents and salient features of any sample.  Crystallography also plays a significant part in the structural determination of materials making up the various constituents of the sample.

As the digitised images will also play a part in the recognition of certain constituents these can be further manipulated permitting viewing using polarised light and other means of illumination.

Our initial problem with some samples (unless taken by DustWatch in the field) is a common one shared by most laboratories running any form of assessment or analysis and that is that samples are supplied “blind” without any background information.  This means that we need to start making assumptions about unknown sampling procedures, exposure or capture times, methods or even any unusual circumstances surrounding the sampling conditions.

It is important to not put two samples together in one container as there will be cross contamination during transport and handling.

 

Gerry F. Kuhn (FMVS, MSAIOH, Grad SE) Chris Loans

(BSc Chemical Engineer, Pr Eng, MSc Public Health)

Doc Number:  0421291124  Date:  29-Apr-21

Appendix A:

___________________Extract from http://www.lakeland-microscopes.co.uk/ub100i.html
(Accessed August 2018)_____

Binocular Microscopes > UB-100i

UB-100i Advanced Binocular Laboratory Microscope 
Full sized laboratory standard instrument of modern ergonomic design, robust reliable construction and excellent optical performance.
Equipped with infinity-corrected achromatic optical system. Chromatic aberrations and field curvature of field are both ideally corrected over the field of view. Infinity objectives, with higher numerical apertures, produce crisp and clear images..
Ideal for use in colleges, universities and professional laboratories over a wide range of biological, medical, veterinary, bacteriological and agricultural applications. Highly recommended.

Technical Specification: 
* Magnification range x40, x100, x400 & x1000
* Paired x10 DIN standard high eyepoint, widefield Plan eyepieces. Field 18mm, eyepoint 21mm
* Infinity achromatic objectives DIN standard Parfocal, parcentred x4(0.13),x10(0.30),40R(0.70),x100R(1.25) oil immersion (R=retractable)
* Bright field ABBE condenser (N.A. 1.25) with colour-coded iris diaphragm scale and filter carrier on fully focusing Substage
* Build in 230v, 6v 20w halogen illumination with continuously variable rotary brightness control
* Co-axial coarse and fine focusing with indexed scale and adjustable focus tension
* Smooth action x-y mechanical stage 142x135mm with co-axial drop controls and an adjustable spring arm to accommodate slides of different sizes		 * Smooth action x-y mechanical stage 142x135mm with co-axial drop controls and an adjustable spring arm to accommodate slides of different sizes
* Seidentopf binocular head, inclined 30 degrees Rotatable 360 degrees with full inter-pupillary adjustment (52-75mm). Magnification factor x1
* Reversed position quadruple objective turret on sealed ball bearing race
* Complete with dust cover
* Supplied in polystyrene pack
* Dimensions 270x190x340mm
* Weight 6.5kg

 

______End of Extract from http://www.lakeland-microscopes.co.uk/ub100i.html (Accessed August 2018) _

Appendix B

Additional reading material (Links accessible in August 2018 but may have changed since then)

Appendix C

Particle Size Theory

The South African national definition of PM10 particulate size is given as particulate matter of a size less than 10 micron.

The definition of any particle size has to include the density and the shape of the particle.  To understand PM10 particulate (or any particle size definition) additional definitions need to be understood and taken into account.

  1. PM10 – Sampling of atmospheric dust where the aerodynamic d50 diameter is 10μm.
  2. Aerodynamic diameter is the diameter of a spherical particle that has a density of 1g/cm3 and which has the same terminal settling velocity as the particle of interest.
  3. d50 – In a sample of dust the d50 diameter is the diameter above which fifty percent of the particles are larger, and below which fifty percent of the particles are smaller.
  4. d90 – In a sample of dust the d90 diameter is the diameter below which 90% of the particles are smaller.
  5. Terminal settling velocity is the fastest velocity that a particle can fall by gravity taking into account the shape and drag of the particle.

WRAC – Wide Range Aerosol Classification

TSP – Total Suspended Particulate

“The percentage of total aerosol mass less than 10 micron varied from about 50 to 90%, depending on the sampling location and sampling conditions.”  (R. M. Burton & Dale A. Lundgren (1987) Wide Range Aerosol Classifier: A Size Selective Sampler for Large

Particles, Aerosol Science and Technology, 6:3, 289-301, DOI: 10.1080/02786828708959140

To link to this article: http://dx.doi.org/10.1080/02786828708959140)

“PM10: The mass concentration of particles smaller than 10 μm. In practice, PM10 samplers do not provide perfectly sharp cuts at 10 μm. Instead, size-dependent collection efficiencies typically decrease from 100 percent at ~ 1.5 μm to 0 percent at ~15 μm, and are equal to 50 percent at 10 μm.” Referenced from http://www.aerosols.eas.gatech.edu/EAS%20Graduate%20Lab/Class%20Notes%20Aerosols%20and%20Size%20Distrn.pdf

From the above it is important to note that larger particles can be collected if they have a low density as is the case with organics.

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