Determination of typical background concentrations of...
Transcript of Determination of typical background concentrations of...
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Determination of typical background concentrations
of asbestos in near-surface soils of selected public
open space areas of England and Wales to define
representative concentrations in areas not expected
to be subject to significant contamination
Chris Collins1, Mark Craggs2, Nicola Harries3, David Wood4, Gary Burdett5
1.Soil Research Centre, University of Reading, Reading, RG6 6DW
2.QUEST,Quaternary Scientific, University of Reading, RG6 6AB
3.CL:AIRE, 32 Bloomsbury Street, London, WC1B 3QJ
4. REC, Osprey House, Pacific Quay, Broadway, Manchester M50 2UE
5. Health & Safety Laboratory (HSL), Buxton, Derbyshire, SK17 9JN, UK
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Summary
A survey of the background asbestos concentrations in the near-surface soils of public open
space across England and Wales was undertaken. Samples (272) were taken from urban
(82), peri-urban (96) and rural locations (94). The sampling distribution was based on a 40 x
40 km grid across England and Wales which provided 111 sampling squares from which the
three sample categories were taken. Samples of near-surface soil were taken from a 20 m x
20 m square in an open location away from buildings, roads and tree cover. The sampling
protocol was based on previous national studies and reviewed by the Project Steering Group
(PSG). No alterations were found necessary following audits in the field.
Samples were quantitatively analysed according to a current UKAS accredited methodology
and in line with the draft Standing Committee of Analysts “Blue Book” method, “The
Quantification of Asbestos in Soil and Associated Materials (v.11)”. The detection limit of
this method is ~0.001% by weight for asbestos fibres and asbestos-containing materials. An
extension of the Blue Book method was adopted to achieve an Limit of Detection (LOD) to
0.0001%. All 272 samples were analysed. This method, based on stereo and polarised light
microscopy, was independently cross-checked by an analytical Transmission Electron
Microscopy (TEM) method using 16 blind samples. A number of asbestos-containing quality
assurance samples which had been spiked with a known amount of asbestos were also
analysed.
Only two samples from 272 field samples gave positive results (i.e. <1% of samples); both of
these were < 0.0002% by weight.
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Members of the Project Steering Group (PSG)
David Middleton – Defra
Richard Clark & Andrew Williams – Welsh Government
Stephen Forster – Chair of the Joint Industry Working Group (JIWG) on Asbestos in Soil and
Construction & Demolition Materials
Simon Cole – SoBRA
Nicola Harries – CL:AIRE
Chris Collins & Mark Craggs – University of Reading
Garry Burdett – Health & Safety Laboratory
David Wood – REC Ltd
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Table of Contents Summary .................................................................................................................................... ii
List of Tables ............................................................................................................................. vi
List of Figures........................................................................................................................... vii
Project aims and objectives ....................................................................................................... 1
Introduction ................................................................................................................................ 3
Methods ..................................................................................................................................... 4
Sampling strategy .................................................................................................................. 4
Sampling protocol .................................................................................................................. 8
Soil analytical process ........................................................................................................... 8
Asbestos analysis by electron microscopy .............................................................................. 11
Quality assurance .................................................................................................................... 12
Auditing ................................................................................................................................ 12
Asbestos analysis ................................................................................................................ 12
Results of the examination of the known QA samples .................................................... 13
Results from the blind analysis of the unidentified QA samples...................................... 14
Outcome of QA ................................................................................................................. 15
Results ..................................................................................................................................... 16
Sampling .............................................................................................................................. 16
Soil concentrations............................................................................................................... 20
Asbestos analysis of environmental samples ..................................................................... 21
Using conventional microscopy and stratified approach ................................................. 21
Comparison of field samples between REC and HSL ..................................................... 21
Discussion ................................................................................................................................ 23
References ............................................................................................................................... 24
Appendices .............................................................................................................................. 25
Appendix 1. Standard Operating Procedure for SP1014 Sampling.................................... 26
Appendix 2. Sample Survey Recording sheet ..................................................................... 35
Appendix 3. Site audit reports ............................................................................................. 37
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Appendix 4 – Audits of Asbestos Analysis .......................................................................... 56
Appendix 5 - Abbreviated Method Statement for Quantification of Asbestos in Soils by REC
Ltd ........................................................................................................................................ 67
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List of Tables
Table 1. Sampling categories as defined by the UK Census data .......................................... 6
Table 2. Results from the ‘known’ and ‘blind’ QA analysis of prepared spiked samples (weight
% of asbestos) undertaken by Health & Safety Laboratories ................................................. 14
Table 3. Final list of samples ................................................................................................... 20
Table 4. Comparison of field samples HSL and REC Ltd ....................................................... 22
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List of Figures
Figure 1. Selected sampling locations based on 40 km grid across England and Wales ........ 5
Figure 2. Sampling locations with 40 km grid overlaid over population data. .......................... 7
Figure 3. Soil analysis process flowsheet ............................................................................... 10
Figure 4. Example site and sample description sheet. ........................................................... 18
Figure 5. Final sample numbers and locations ....................................................................... 19
Figure 6. Asbestos concentrations results as presented by REC Ltd after light microscopy
analysis. ................................................................................................................................... 20
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Project aims and objectives
Aim
To provide an estimate of the range of typical background concentrations of dispersed
asbestos fibres in soil across England and Wales that are primarily a result of atmospheric
dispersion and deposition of fibres from the historic import of asbestos and the manufacture
and use of asbestos-containing products.
It was not the aim of this project to establish the range of asbestos fibre or asbestos-
containing material in soil concentrations resulting from localised occurrence of asbestos in
the ground as a result of the disposal of waste or by other mechanisms such as demolition of
buildings that may have incorporated asbestos-containing materials. The survey specifically
avoided land areas where elevated concentrations of asbestos were known or strongly
suspected (for example former asbestos manufacturing facilities or manufacturing facilities
that extensively used asbestos, and areas of naturally occurring asbestos).
Objectives
• Design a survey and sampling approach which were capable of obtaining a dataset
that is amenable to relevant, robust statistical analysis and provide a reliable dataset
that can withstand public scrutiny.
• Target surface soils in publicly accessible areas e.g. open spaces or land where
access can be provided by Defra, Welsh Government or local authorities that are not
likely to have been subject to the addition of former building materials or any other
potentially asbestos containing materials.
• The survey should be capable as a minimum of distinguishing between urban and
rural soils, but should aim to provide as much land-use discretisation as is practicable
such that robust correlations can be made.
• The survey should avoid spatial biasing where practicable.
• The survey should anonymise samples and sample locations in the final report, but
sample locations should be suitably recorded so that they can be used in the data
interpretation to ascertain spatial and land-use correlations where appropriate.
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Scope
The survey should avoid areas of naturally occurring asbestos, areas affected by major
asbestos industries (for example the former Cape and Turner Brothers factories), areas
where asbestos waste has been placed in the ground, brownfield sites, and made ground
comprising building demolition rubble. For rural areas locations should avoid land which
may contain asbestos – this might include agricultural land in and around farmsteads and
rural commercial properties, as well as former farm tip sites and old quarry holes.
The soil sampling protocol should provide representative samples of soil for subsequent
analysis. The protocol should focus on the assumption that asbestos might be present as
dispersed free fibres in soil, but should also be capable of accounting for fragments of
asbestos-containing material (ACM) if observed. The protocol should also provide sufficient
qualitative information on the sampling location to aid subsequent interpretation of the
analytical results.
The survey and sampling designs will be agreed with the PSG. Existing guidance on soil
surveys and sampling techniques should be referenced, and consideration should also be
given to the preliminary thoughts of the PSG as provided.
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Introduction
To inform scientifically robust risk-based decisions to protect employees and the public from
asbestos in soil, it is essential to develop a scientifically defensible and pragmatic risk
management system when dealing with asbestos in soil. In ensuring that risk assessment
outputs are pragmatic, knowledge of background concentrations are required to inform
decision making within the Part 2A statutory guidance and planning decisions. The concept
for this is similar to that already published for other soil contaminants as part of the revised
Soil Guideline Values programme in 2009.
This research sampled across England and Wales to define typical background
concentrations in areas not expected to be subject to asbestos contamination (for example
small grassed areas in residential estates or playing fields rather than roadside verges).
Prior to this survey, there has not been any investigation to ascertain background
concentrations of asbestos in soil, however the British Geological Survey had carried out a
survey for Defra on determining normal background concentrations of a number of other
common contaminants [1]. In addition Defra and the Welsh Government have previously
carried out soil and herbage surveys [2] for a range of contaminants. This current research
project drew on these two projects when planning its approach and sampling protocols.
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Methods
Sampling strategy
To provide a national sample distribution a 40 km grid covering England and Wales1 was
created using ArcGIS v10.2.2 Grid Index Features tool, this grid produced 133 sampling
squares. The Create Fishnet tool was then applied to produce centre points on the newly
created grid (Figure 1). A selection was performed to remove squares mainly comprising sea
which left 111 squares to be potentially sampled. Middle Layer Super Output Area (MSOA)
census data for England and Wales [3], were downloaded and three classifications were
assigned to the MSOA landuse categories: urban, peri-urban and rural (Table 1 and Figure
2).
The intention was to take one sub-sample from each of the land use categories (urban, peri-
urban and rural) from each sampling area; potentially providing 333 samples.
The Local Authorities (LAs) in England and Wales in whose area the land within which each
grid square centre was located were first contacted and suitable sampling locations selected
and agreed. A specific land use category was then assigned, i.e. urban, peri-urban or rural.
The nearest locations for the remaining sample categories were then chosen using Google
EarthTM. Duplicate samples were taken at 5.6 % of the plotted sites to determine within-site
variability.
This sampling strategy was reviewed by the Project Steering Group (PSG) and accepted
after several iterations. Prior to the actual sampling exercise being undertaken, University of
Reading (UoR) contacted each of the to arrange for the sampling of soil in their respective
area.
1 England and Wales boundaries downloaded from (http://census.edina.ac.uk/
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Figure 1. Selected sampling locations based on 40 km grid across England and Wales
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Table 1. Sampling categories as defined by the UK Census data [4]
MSOA categories Project categories
England Urban minor conurbation
Urban
England Urban major conurbation
England Urban city and town
Wales Urban city and town
England Urban city and town in a sparse setting
Peri-urban
Wales Urban city and town in a sparse setting
England Rural town and fringe
England Rural town and fringe in a sparse setting
Wales Rural town and fringe
Wales Rural town and fringe in a sparse setting
England Rural village and dispersed in a sparse setting
Rural
England Rural village and dispersed
Wales Rural village and dispersed
Wales Rural village and dispersed in a sparse setting
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Figure 2. Sampling locations with 40 km grid overlaid over population data.
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Sampling protocol
The collection of soil samples followed the protocol adapted from Defra and BGS when
undertaking the herbage and soil survey for England and Wales [2] and the GBASE surveys
[1] respectively. Five samples were taken from the corners and central location within a 20m
x 20m square avoiding areas beneath mature trees. A smaller square of greater than 10m x
10m was permitted if space was restricted, however any reduction was noted on the site
sampling sheet (Figure 4). At each site a location reading was taken by a hand held GPS
(+/- 10 m) and site details logged in accordance with sample sheet and photographed
(Plates 1a-d). Careful notes were also made of buildings that were close by and the fabric
materials they were made of. The surface herbage was removed with hand tools and a 5 cm
depth of soil taken using a stainless steel spade and/or trowel. Vegetation removal focused
on above-ground vegetation clearance to facilitate the soil sampling; the removal of soil was
avoided except when tightly-bound by dense root mats. For example, it was deemed
acceptable to remove the top 1cm beneath grass turf as this soil typically came away with
the turf when raised. The five samples were bulked to form one sample (2 kg +/- 10g, scale
precision 0.1g); this was coned and quartered with approximately a 1 kg sample being
retained for analysis by REC Ltd and a further 1 kg of material being retained for storage at
UoR. There was no further processing of the sample.
After sampling at each site, all tools and trays were cleaned with disposable wipes and
stored in clean bags to prevent cross contamination. All samples were systematically
anonymised and labels were only traceable to sites by UoR staff. Sample anonymisation
was based on 256 bit AES encryption with a password 64 hex characters in length. Any
images produced as part of the sampling process had their metadata stripped thereby
removing any embedded location data in the image file. Sampling data was stored at UoR
and could only be accessed by one staff member.
As with the sampling strategy the sampling protocol was critically reviewed over several
iterations by the PSG. The detailed Standard Operating Procedure (SOP) for the sampling
procedure is elaborated in Appendix 1.
Soil analytical process
REC Ltd performed quantitative stratified light microscopy analysis according to their current
UKAS accredited methodology and is broadly in line with the Blue Book method, “The
Quantification of Asbestos in Soil and Associated Materials (draft v.11)”. One variation
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was performed whereby, even if no fibres were detected at the first stage of the analysis,
suspensions were prepared and a total of 10 aliquots were taken for filtration and
microscopic analysis. The objective here was to lower the limit of detection and hence the
reporting limit to 0.0001% and to improve the uncertainty of measurement.
The analytical approach followed a 3-stage process of visual inspection, microscopic and
gravimetric evaluation and microscopic evaluation of an aqueous suspension. This standard
analytical methodology generates three natural cut-off points for analysis at the three stages,
with Stage 3 normally offering a reporting limit of 0.001%.
The analysis consisted of the following stages which are carried out after drying as
described in the flow chart below (Figure 3).
Stage 1 – No samples were stopped at Stage 1
Stage 2 – Gross contamination (>0.1%)
Stage 3 – Result <0.1% - 0.001%
Stage 4 – Result or >0.0001% (0.001% and above UKAS accredited)
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Figure 3. Soil analysis process flowsheet
Stage 1 Visual analysis performed on 1 kg soil plus microscopic
analysis of subsample for fibres and small ACM pieces
Stage 2 >20 g subsample analysed under microscope,
fibre clumps and ACM’s removed, identified and
weighed with material removed at Stage 1
If no asbestos detected
or suspected fines only
are found in the sample,
analysis proceeds
directly to Stage 3
If fibre clumps and/or
pieces of suspected
ACMs are found
analysis proceeds to
Stage 2
<0.1% proceeds to
Stage 3
Stage 3 Suspension in 300 ml water, 1ml aliquot filtered taken and 200
graticules counted.
Stage 4 Further 9 x 1 ml aliquots filtered of the suspension taken
and 200 graticules per aliquot counted
<0.001% proceeds to
Stage 4
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Asbestos analysis by transmission electron microscopy
The Health and Safety Laboratory (HSL) analysed 19 samples in total for this project; three
samples as a laboratory comparison between REC Ltd and HSL which included standards
and blanks; 16 field samples were sent to HSL by REC Ltd. The field samples consisted of
12 selected samples one from each category (urban, peri-urban, rural) in the north, east,
south and west of the sample grid, two random field samples and two field samples where
asbestos had been detected by REC Ltd. All samples had been anonymised by the
University of Reading and were blind analyses.
The duplicate samples were analysed using HSL’s UKAS accredited method for asbestos in
soil, which is based on the International Standard method ISO13794 [5]. This method uses
analytical Transmission Electron Microscopy (TEM) to quantitatively identify asbestos fibres
in a known area of the filter. However, as most of the TEM analysis was carried out in the
latter stages of the project, it was decided to change from the original planned stratified
method of analysis (based on analysis at two magnifications) to a more sensitive method
which used a single magnification of x 5,600 to search a larger area (0.96 mm2 ) of the filter
for both >5 µm long fibres and any visible fibres. The high contrast and high definition CCD
camera images allow both shorter and thinner fibres to be detected. To further optimise the
analytical sensitivity most of the filters analysed were prepared by HSL from soil sub-
samples sent to HSL.
Any fibres (particles with an aspect ratio of >3:1 and with parallel or stepped sides) or
bundles of fibres found were analysed using a combination of energy dispersive x-ray
analysis and selective area electron diffraction to identify whether they were asbestos and, if
so, which type. Any asbestos fibres/bundles identified were counted and then sized at higher
magnifications and their volume and mass calculated. Results were calculated and reported
in terms of the asbestos weight % and the number of asbestos fibres/g of soil. Any >5 µm
long fibres with widths >0.2 µm are likely to be counted by the regulatory method for air
sampling (HSG 248) based on phase contrast microscopy (PCM) and were reported as PCM
equivalent fibres (PCME).
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Quality assurance
Auditing
Both internal and external audits were undertaken of the field sampling methodology and the
analysis of soils for asbestos. For the field sampling, the site preparation and soil collection
were assessed using the procedures outlined in Appendix 1, Section 8. Three audits were
undertaken by two external assessors (Appendix 3). The soil analysis was audited against
the method statement (see Appendix 5 for the abbreviated method statement). Two audits
were undertaken, one internal and one external (Appendix 4). No additional auditing of the
TEM analysis was carried out due to the low number of samples analysed. The audit
procedure was designed to provide confidence that field and laboratory procedures
developed were being undertaken to a high standard.
Asbestos analysis
To assess the REC Ltd laboratory performance, a number of “spiked” soil samples
containing known added amounts of asbestos were distributed for analysis. The first round
of assessment involved sending two samples directly to REC Ltd for analysis (LCSA 1,
DLSA 5). Each of these samples contained a known amount of amosite fibre which had
been prepared and analysed previously by HSL and were identifiable as non-routine QA
samples.
Three further QA samples were prepared by mixing either an asbestos-containing material
or asbestos fibres into 500 g of a loam soil. One sample (1 DLS) contained two small pieces
(each less than the size of a fingernail) of dry asbestos cement containing chrysotile (AIMS
52 sample 2) weighing 0.3350g. The calculated amount of asbestos was based on the
asbestos cement containing 10% of asbestos by weight. These pieces were considered
large enough to identify during the stage 1 visual examination of the 1 litre sample when
spread out on a tray followed by asbestos identification analysis. The second sample (2
DLS) had 12.75mg of ultrasonically dispersed chrysotile fibre in water added. The chrysotile
was visible to the eye when added to the soil before mixing in a figure of eight mixer but this
would have been further dispersed and coated with soil particles during the mixing process.
The third sample (3 DLS) had no additional asbestos added and was used to check that the
loam soil used for the preparation of the QA samples was not already contaminated with
asbestos.
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These three QA samples were sent to University of Reading where they were mixed with a
further 500g of soil from known blank field samples and repackaged and given anonymised
numbers so they were indistinguishable from the other study samples (1- 3 DLS). These
three samples were therefore “blind” analysis QA samples. These three samples were
analysed “blind” by both REC Ltd and HSL using their standard analytical protocols for this
study.
Results of the examination of the known QA samples
The first two known QA samples prepared by HSL were correctly reported by REC Ltd as
containing amosite asbestos (LCSA1 & DLSA5), but the mass percentage in each was
underestimated (see Table 2). Subsequent investigations showed that this was partly due to
the method used in stages 1 & 2 (Figure 3) to report the weight percentage which was based
on picking out fibres from the soil substrate and weighing them on a balance. This gave rise
to two issues – when picking out fibres and suspect pieces of ACM, whilst this is the
established first stage of the procedure employed by REC Ltd, it is only likely to give
accurate results if the majority of the asbestos is easily seen and/or present in easily
identifiable pieces, and if enough of it can be separated from the soil matrix to give good
precision and accuracy when weighed. As only fibres of amosite were added to the two
known QA samples, any fibre picking would only remove any of the larger fibre bundles and
clumps of fibres and give an underestimate of the total mass of asbestos present. This would
particularly be an issue when the asbestos had been relatively well dispersed in the soil
matrix and was mainly present as individual fibres, as it was in these two samples.
It was also noted at the limit of detection (LOD) for stages 1 & 2 (i.e. 0.001%) meant that the
balance used for the weighing was at the limit of its resolution and had limited precision.
However, the visual examination in stages 1 & 2 (fibre picking and stereo-microscopy) both
found the presence of finely-divided amosite fibres and REC Ltd reported it correctly as
being <0.001% (Note samples DLSA5 had been examined previously and two small fibre
bundles would have been extracted for identification).
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Table 2. Results from the ‘known’ and ‘blind’ QA analysis of prepared spiked samples (weight % of asbestos) undertaken by
REC Ltd
HSL
sample # Anonymised Sample from
UoR
Type and amount of asbestos
(%) added by
HSL
Type and amount of asbestos
(%) reported stages 1
& 2
Type and amount of asbestos
(%) reported
stages 3 & 4
HSL TEM analysis
No of fibres
counted
Amount of
asbestos reported
(%)
Concentration (x106 fibres/g) of
bulk material
LCSA1* (100g sample in a bottle)
Known QA sample
Amosite fibres (0.001)
Amosite (<0.001)
Amosite (0.0003)
Not analysed
Not analysed
Not analysed
DLSA5* (36 g sample in a Petri dish)
Known QA sample
Amosite fibres (0.01)
Amosite (<0.001)
Amosite (0.0007)
Not analysed
Not analysed
Not analysed
DLS 1 S138
Blind sample
2 pieces of chrysotile asbestos cement (0.003)
Chrysotile (0.003)
Chrysotile 0.011
0 ND <0.0666
DLS 2 S258 Blind sample
Finely dispersed chrysotile fibres (0.0013)
Not detected (<0.0001)
Not detected (<0.0001)
0 ND <0.1106**
DLS 3 S259 Blind sample
Blank Not detected (<0.0001)
Not detected (<0.0001)
Not analysed
Not analysed
Not analysed
*These samples were prepared by HSL and sent directly to REC Ltd ** Note: Five >5 µm long chrysotile fibres with widths <0.2 µm were found in this sample with a calculated mass of 0.0000021% and a fibre concentration of 0.186 x 106 f/g
Results from the blind analysis of the unidentified QA samples
Blind analysis of these three QA samples by REC Ltd found the asbestos cement fragments
(DLS 1), but did not detect the finely dispersed chrysotile (DLS 2), and confirmed that
asbestos was not detected in the blank sample of soil (DLS 3) (Table 2.).
The TEM analysis of sample DLS 2 subsequently undertaken by HSL found that chrysotile
asbestos was present (Table 2.). However, all of the chrysotile fibres analysed had
diameters of <0.2 µm and would be too thin to be visible by light microscopy analysis. The
fineness of the fibres in this sample explained the negative result for sample DLS 2 by REC
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Ltd. The mass of chrysotile calculated by the TEM analysis was 0.0003% well below the
actual mass percent added 0.0013%.
The sample supplied for TEM preparation was only 0.1% of the sample, so the mixing of the
small amount of chrysotile into this soil would have to be very good and the sub-sampling
representative of the original sample, both of which are challenging. The non-detect TEM
result for sample DLS 1 is explained by there only being two pieces of asbestos cement
added, which were found and extracted from the sample during stage 1 of the analysis
conducted by REC Ltd. No asbestos was added to DSL 3 which was the soil used for DLS 1
& 2 which confirmed that there was no detectable asbestos present.
Outcome of QA
All of the QA analysis was in some way challenging with small amounts of asbestos added
at or below 0.01% and generally were closer to the limit of detection for most routine soil
analyses (0.001%). The four stage REC Ltd analysis correctly identified the presence of
asbestos except in one very challenging sample where the chrysotile fibres appeared to be
too thin to be seen by light microscopy. The estimation of mass did not have good precision
but due to the low amounts added this is to be expected. What was shown was that the
overall method using visual assessment of the whole 1 kg sample to microscopic
examination of filtered aliquots is needed to identify the different forms of ACMs and
asbestos fibres that may be present.
The QA results give a reasonable degree of confidence that the REC Ltd analysis would
have had a good chance of detecting asbestos being present in the survey samples, if
present in concentrations of >0.0001%, unless the fibres were outside the size criteria for the
assessment of airborne risk.
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Results
Sampling
Of the 333 sites scoped by the initial sampling strategy, 288 were identified as suitable
following further assessment. The reduction in the final number of sampling locations is
attributed to the fact that not all of the three categories of land use were present in each grid
square.
Once sites were identified, sampling proceeded without significant difficulties. The protocol
worked well and the recording of site characteristics was relatively straightforward (Plates
1a-d, Figure 4). The proportions of rural (35.3%), peri-urban (34.6%) and urban locations
(30.1%) were well-balanced to ensure no bias in the data. There was also good coverage
across the whole sample area with only 1 grid square un-sampled. In those squares where
all three samples categories were not taken this was often because a category was not
present, e.g. urban locations on the England-Scotland border.
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(a) (b)
(c) (d)
Plate 1 a-d sampling photos relating to site described in Figure 4.
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Figure 4. Example site and sample description sheet.
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Figure 5. Final sample numbers and locations
NS
NS Natural
As
Not Sampled (due to geology)
Not Sampled (No central sampling location generated, generally greater proportion of ocean relative to land.
x/y
Done
x/y LA contacted, ‘x’ sites out of ‘y’ total sites identified and permission to sample/access available.
Sampled locations ‘x’ sites out of ‘y’ total sites within grid.
0/3 LA contacted, meaningful discussion has taken place but nothing yet identified.
x/y
Done Indicates partial grid completion (at least 1 site will l not be sampled)
Key
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Table 3. Final list of samples
Country Urban Peri-urban
Rural
England 76 82 80
Wales 6 14 14
Total 82 96 94
Grand total 272
Soil concentrations
Samples were typically analysed by REC Ltd in batches of 20 with results usually returned
within 4 weeks in a standardised format indicating the concentrations at the different
analytical stages (Figure 3 and 6).
Figure 6. Asbestos concentrations results as presented by REC Ltd after light microscopy analysis.
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Asbestos analysis of environmental samples
Using conventional microscopy and stratified approach
Asbestos was detected in two samples of the 272 analysed, i.e. less than 1% of the total of
all samples submitted to REC Ltd for analysis. These were from a peri-urban site
(<0.0001%, S137) and an urban site (0.0002%, S161).
Comparison of field samples between REC and HSL
To validate the results from the stratified light microscopy (REC Ltd) with the TEM (HSL) 16
samples were used for duplicate analysis (Table 4.). No asbestos was detected in any of the
samples by HSL including the two positive detects (S137, S161) reported by REC discussed
above. Both of these samples were later sent to HSL for further checking and analysis and
prolonged searching using stages 1 an 2, did not detect any further asbestos fibres in these
samples.
It appears that the non-detect by TEM was a consequence of the low concentrations of
asbestos in these samples and their non-homogeneous nature (e.g. one sample had a
single bundle picked out in stage 1), whereby any sub-sample was more likely to be free of
asbestos.
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Table 4. Comparison of field samples HSL and REC Ltd
HSL analysis
Asbestos structures > 5 µm long (PCME) REC Ltd Analysis
Client sample No.
Analytical sensitivity
(x106 structures/g) of bulk material
No of fibres
counted
mass %
Maximum possible concentration
(x106 structures/g) of bulk material
mass %
Maximum possibile
concentration (%)
S041 0.037 0 ND <0.111 ND <0.0001
S084 0.022 0 ND <0.0663 ND <0.0001
S092 0.022 0 ND <0.0665 ND <0.0001
S098 0.022 0 ND <0.0661 ND <0.0001
S100 0.037 0 ND <0.112 ND <0.0001
S119 0.037 0 ND <0.112 ND <0.0001
S130 0.037 0 ND <0.112 ND <0.0001
S146 0.037 0 ND <0.111 ND <0.0001
S147 0.037 0 ND <0.11 ND <0.0001
S076 0.022 0 ND <0.0665 ND <0.0001
S173 0.022 0 ND <0.0668 ND <0.0001
S066 0.019 0 ND <0.058 ND <0.0001
S137 0.022 0 ND <0.0666 <0.0001 NA
S161 0.111 0 ND <0.333 0.0002 NA
S088 0.019 0 ND <0.058 ND <0.0001
S089 0.039 0 ND <0.117 ND <0.0001
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Discussion
The sampling of near-surface soils across England and Wales was successfully completed
with 94% of the original targeted samples collected. There were two reasons for samples not
to be taken from a grid location; i) the particular category was not present e.g. no urban
sample on the England-Scotland border, or ii) lack of cooperation from the landowner.
Two samples from 272 gave positive results, i.e. <1%; these were at low concentrations
<0.0001 and 0.0002% and close to the expected detection limit. In both positive cases loose
fibres of amosite were observed. This number of samples where asbestos was positively
detected is too small to enable a discussion of any trends in the data, or to estimate a
‘background concentration’ for England and Wales.
The results do give confidence, however, that ‘background concentrations’ of asbestos in
near-surface soils following the removal of surface vegetation in public open spaces across
the spectrum of land uses are generally likely to be very low and unlikely to be detected by
the standard analytical methodology. This also gives a degree of confidence that significant
potential health risks arising from ‘background concentrations’ of asbestos in near-surface
soils in public open spaces unlikely to be of concern.
The very small number of positive detects (<1% of the total samples analysed and reported
in this survey) will give added weight that asbestos found in near-surface soils is likely to be
due to local contamination sources (e.g. demolition, waste disposal and fly-tipping) and that
the extent of these sources can be mapped by soil sampling surveys. It is not evident from
this survey that historic diffuse airborne fibre release has resulted in widespread detectable
quantities of asbestos in near-surface soil across England and Wales.
The main aim of the study was met because the soil concentrations were measured at less
than 0.0001% by light microscopy. If consideration is given to the TEM results produced by
HSL, this concentration could be even lower as shown in Table 4 where the maximum
possible concentration detectable (limit of quantification) is shown for the 16 duplicate QA
samples to be in the range of <0.58 to <0.11 x106 structures/g of bulk material.
24
References
1. Ander, E.L., et al., Methodology for the determination of normal background concentrations of contaminants in English soil. Science of The Total Environment, 2013. 454-455: p. 604-618.
2. Agency, E., Volume 1. Introduction and Summary. UK Soil and Herbage Pollutant Survey. 2007: Environment Agency.
3. Pateman, T. Rural and urban areas: comparing lives using rural/urban classifications. Regional Trends, 20101. 43.
4. Statistics, O.o.N., Middle Super Output Area Mid-Year Population Estimates. 2014. 5. 13794, I., Ambient air - Determination of asbestos fibres - indirect transfer
transmission electron microscopy method, I.S. Organisation, Editor. 1999 Geneva. Switzerland.
25
Appendices
26
Appendix 1. Standard Operating Procedure for SP1014 Sampling
1 Scope and Application
The purpose of this standard operating procedure (SOP) is to describe the procedures for
the collection of representative surface soil samples. The sampling depths required for
SP1014 are easily reached without the use of drill rigs, direct push or other mechanised
equipment. Analysis of soil samples for asbestos will be used to produce summary statistics
(such as 5th and 95th percentile, median and mean). These are standard (typically
applicable) operating procedures which may be varied or changed as required, dependent
upon site conditions, equipment limitations or limitations imposed by the procedure. In all
instances, the actual procedures used to collect samples will be documented and described
in an appropriate site report.
2 Method Summary
Soil samples may be collected using a variety of methods and equipment depending on the
depth of the desired sample, the type of sample required and the soil type. As we are
focusing on near surface sampling and are not required to sample undisturbed soil samples
(i.e. samples generated by soil coring) the use of spades, trowels and scoops is sufficient.
These collection methods will generate disturbed samples however, as the 5 samples from
each site are bulked into a single unit.
3 Sample Containers, Handling and Storage
For each sampling site, 2 kg (400 g from each corner and centre of a 20 m x 20 m sampling
grid) of soil will be placed into an appropriately sized plastic containers clearly marked with
sample identification information. Half will be sent for analysis and half stored for a period of
at least 1 year.
4 Interferences and Potential Problems
There are two primary potential problems associated with soil sampling. These are cross
contamination of samples and improper sample collection.
a) Cross contamination problems can be eliminated or minimised through the use of
dedicated sampling equipment. If this is not possible or practical, then
decontamination of sampling equipment is necessary. In addition clean and
potentially dirty areas need to be kept separate in the collection vehicle. The latter
27
will contain all collected samples, sampling equipment and used clothing and barrier
protection.
b) Improper sample collection can involve using contaminated equipment, failure to
adhere to sampling grid or sampling at an incorrect depth, or failure to identify
asbestos samples where present, resulting in variable, non-representative results.
This is addressed in detail below Section 8.
5 Asbestos Risks
5.1 Human Health
Asbestos fibres do not dissolve in water or evaporate; they are resistant to heat, fire
chemical and biological degradation and are mechanically strong. The globally harmonised
system of classification and labelling for chemicals indicates asbestos is a category 1A
carcinogen. All types of asbestos fibres are known to cause serious health hazards in
humans.
The specific risks from asbestos relate to the potential release of respirable fibres into the
atmosphere when disturbed. Outdoors, asbestos fibres or dust, once exposed, may be
released into the atmosphere by the wind, by construction activities or by the movement of
vehicles or construction plant and will undergo significant dilution at increasing distance from
the source. Even low concentrations of asbestos fibres in air can present a potential risk to
health if exposure to those concentrations is prolonged. Potential risk to health is a function
of concentration and exposure duration.
Some asbestos-containing materials (ACMs) are more inclined to release fibres than others;
for example, asbestos fibres bound in thermoplastics, resins or cement release fewer fibres
than loose, friable insulation. It is of some note that ACMs installed in buildings, which are
normally dry, tend to release more fibres when disturbed than the equivalent ACMs when
encountered in soil, where they tend to be wet.
5.2 Exposure Limits (air)
In the UK an unacceptable risk to human health from the inhalation of asbestos fibres is
reported by the Health and Safety Executive (HSE). As a consequence of this the following
regulations apply. These set out legal duties and it is important to comply with any
requirements derived from the regulations. The regulations provide minimum standards for
protecting employees from the risks associated with asbestos.
28
There are two main limits set out in regulation 2 of the Control of Asbestos Regulations
2012. The first relates to the concentration of asbestos fibres in any localised atmosphere
(control limit) and the second relates to sporadic and low intensity exposure. The latter is
sometimes referred to as the short-term exposure limit (STEL).
The control limit refers a concentration of asbestos in the atmosphere when measured in
accordance with the 1997 WHO recommended method, or by a method giving equivalent
results to that method approved by the Executive, of 0.1 fibres per cubic centimetre of air
averaged over a continuous period of 4 hours.
For the purposes of regulation 2, for exposure to be sporadic and of low intensity, the
concentration of asbestos in the atmosphere should not exceed or be liable to exceed 0.6
fibres per cubic centimetre (f/cm3) in the air measured over a ten-minute period. Any
exposure which exceeds or is liable to exceed this is not sporadic and of low intensity. Note
that this approved concentration for sporadic and low intensity exposure is not the same as
the ‘control limit’ defined in regulation 2 of the Control of Asbestos Regulations 2012.
It is relatively easy to release asbestos fibres when working with asbestos coatings,
asbestos insulation, and asbestos insulating board (AIB). In most cases, only those with a
licence should carry out work with these materials. However, licensing does not apply to
short-duration work on insulation and AIB where the risk assessment shows work carried out
will only produce sporadic and low intensity exposure and will not exceed the STEL.
Licensing does not apply to sampling ACMs in buildings or in soil unless the control limit is
likely to be exceeded.
It should be noted that the Health Protection Agency (HPA) have suggested that where
possible, aim to reduce levels of exposure to as low as reasonably practicable (ALARP).
There are no safe exposures and the hazardous waste threshold of asbestos (≥0.1% wt/wt)
cannot be used as a minimal threshold for human health risk assessment purposes.
5.3 Moisture Content and Drying
Studies have demonstrated that the addition of 10% of water to soil decreases the risk of the
potential release of asbestos fibres to air by a factor between 2 and 10. Most soil is damp
when in-situ and poses little risk of fibre release, but once excavated or exposed it may
become dry very quickly. Locations commonly identified on sites having this potential are
excavations or intrusive hole locations, spoil, areas where any hard surfacing is removed,
vehicle routes passing between soft ground and hard standing, open skips and
29
mudded/soiled boots and clothing. If the site presents dry, well-drained by coarse-grained
granular soil or fill at the surface, the fibres tend to become airborne more readily. The
presence of any airborne dust is a sign of potential immediate hazard.
6 Safety Equipment (PPE & RPE)
It is unlikely that asbestos in the form of dry, loose friable ACMs will be encountered during
sampling, since the sampling strategy has been designed to specifically avoid known areas
of asbestos contamination. If it is encountered, however, then appropriate steps will be
taken to ensure compliance with the Control of Asbestos Regulations (2012). The following
suggestions are taken from em6 asbestos essentials (HSE, 2012):
Overalls
• Disposable Category 3 Type 5/6 (BS EN ISO 13982-1) ideally blue in colour are
suitable.
• Wear one size too big to prevent ripping at the seams.
• Seal loose cuffs with tape if necessary.
• Wear overall legs over footwear.
• Wear hood over RPE straps.
• Dispose of used overall as asbestos waste.
Gloves
• Single use disposable gloves. If latex gloves are required use only ‘low protein
powder-free’ versions.
• Dispose of used gloves as asbestos waste.
Footwear
• Boots are preferable to disposable overshoes which cause a slipping risk.
• Avoid laced boots, these are difficult to clean properly. Keep trousers inside boots to
reduce soil contact.
Respiratory protective equipment (RPE)
• Use suitable RPE with an Assigned Protection Factor of 20 or more.
➢ A disposable respirator to standards EN149 (type FFP3) or EN1827 (type
FMP3);
30
• Face fit testing will be undertaken
• Disposal of RPE is also required.
• Removal of facial hair (no beard/stubble) is important to ensure a good seal of the
mask to the face.
• RPE should only be used for a continuous period of 1 hour after which the wearer
should take a break.
Personal decontamination equipment
• Disposable ‘wet wipes’
• Bucket, clean water and rags.
7 Equipment
Soil sampling equipment includes the following:
• Maps/plot plan
• Safety equipment as specified in 6.
• Global positioning system (GPS) to locate sampling points
• Tape measure
• Survey stakes or flags to map sampling area
• Digital camera
• Appropriate size sample containers
• Ziplock plastic bags (to contain asbestos fragments if encountered)
• Logbook
• Field data sheets and sample labels
• Equipment decontamination supplies/equipment
• Spade and Shovel
• Spatula
• Scoop
• Plastic or metal spoons
• Trowel(s)
• Tool for removing surface herbage (similar to a sod cutter)*
• Water storage tank (5 L)
• Water Spray Bottle
• Portable scales (capable of weighing up to 5 kg +/- )
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* The Statement of Requirement for the England and Wales Soil Background Project states:
‘Vegetation removal should focus on above ground vegetation clearance to facilitate the soil
sampling and the removal of soil should be avoided except when tightly bound by dense root
mats. For example it is acceptable to remove the top 1 cm beneath grass turf.’
8 Procedures
8.1 Preparation
a) Prepare a suitable and sufficient Health and Safety Risk Assessment (see attached
document this will be updated on site).
b) Determine the extent of the sampling effort, the sampling methods to be employed
and the types and amounts of equipment and supplies required.
c) Obtain necessary sampling equipment, and ensure that it is in working order.
d) Prepare schedules and coordinate with staff, client and regulatory agencies to ensure
site access and agreement to sample.
e) Perform a general site survey prior to site entry in accordance with the investigation
Health and Safety Risk Assessment.
f) Perform a site walkover and take images of the site location and record site
properties. Enter these on the sample collection sheet.
g) Use stakes, flagging, or buoys to identify and mark all sampling locations within the
grid. The proposed locations may be adjusted based on site access, property
boundaries, and surface obstructions.
8.2 When asbestos is encountered
Adequate information, instruction and training of persons who may be exposed to asbestos
during the course of their work is required by Regulation 10 of the Control of Asbestos
Regulations 2012.
As this soil sampling exercise could potentially involve encountering asbestos in the ground,
it will only be undertaken by Mark Craggs or Daniel Young, both of whom have received
asbestos awareness training to enable them to avoid being exposed to asebstos during their
work. Other support staff on site will not come into contact with the soil samples.
32
While unlikely, when encountering substantial bulk asbestos in the ground, e.g. lagging,
significant loose fibres, sprayed thermal/plumbing/chemical/electrical insulation, there will be
no attempt to sample such materials. The Local Authority (LA) will be contacted if these
materials are encountered.
If visible but small fragments of ACM are present these will be sampled and placed in a
secure container and, in addition to normal labelling, labelled (standard asbestos ‘a’ label) as
suspected of containing asbestos material including whether or not it is discernible or
suspected ACM. Double bag any non-soil associated asbestos fragments and adequately
label again. Other samples from the five selected within the quadrat will be sampled using
the standard procedure, i.e. bulked before cone and quartering.
Risk, in any event, will be controlled and reduced to ALARP by:
a) The material is in the ground
b) It will be dampened down to prevent suspension of fibres
c) Sampling is outdoors therefore they is rapid dilution of sample concentrations if fibres become suspended
d) Minimal disturbance techniques will be employed
e) PPE/RPE are commensurate with the potential risk
CAR 2012 requires that in the event of an accident, incident or emergency an employer
must, amongst other things, take immediate steps to: 1) Mitigate the effects of the event 2)
Restore the situation to normal, and 3) Inform any person who may be affected.
8.3 Sample Collection
For each of the 5 sampling locations (each grid corner and centre) the following should be
performed:
1. Put on new protective gloves
2. Collect and weigh an appropriate container and enter onto the site collection sheet.
3. Start a central sampling point (middle) and verify using GPS.
4. Dampen down the soil with water spray.
33
5. Carefully remove the top layer of herbage with a pre-cleaned spade or sod cutter ensuring excess soil is not removed.
6. N.B. If fragments are visible go to fit the disposable respirator provided and dampen soil and fragments liberally then place the fragments in a separate Ziplock bag and the soil sample in its own container with full details of sample location.
7. If soil looks dry dampen down again.
8. Using a pre-cleaned scoop, spoon or trowel sample c. 400 g of soil to a depth of 5 cm and place in a pile onto a large plastic sheet
9. Repeat this process for the 4 corners of the quadrat adding the 4 sets of 800 g soil to the central pile.
10. You now have c.2 kg of soil in a pile. Dampen pile, repeat as necessary to reduce potential fibre release.
11. Perform a soil texture analysis using your fingers (keep your gloves on), note down texture/colour/organic matter and horizon(s) sampled.
12. Go around the pile twice moving soil from the edges of the pile to the top to ensure good homogenisation of sample.
13. Split the pile into 4 equal parts (1 kg each).
14. Place two opposite quarters into a sample container (i.e. two samples one for
analysis, one for storage)
15. One of the non-discarded corners will make up the 1 kg sample to be picked up by SAL the other will be the stored sample.
16. Seal the container, weigh and place in crate within van in the designated ‘dirty’ area.
17. Complete the sample collection sheet.
18. Get work partner to confirm all details on the collection sheet.
19. Take a photo of sample collection sheet.
20. Clean sampling equipment
21. Place all used gloves, wipes, overalls and potentially other contaminated materials in disposal bags.
22. Remove mud from boots, wash hands.
34
8.4 Waste Disposal
Gloves are changed after each sample and are disposed of separately to waste suspected
of asbestos contamination. The same applies for any other non-contaminated waste
generated during sampling.
PPE suspected of being contaminated by asbestos or other contaminants will be disposed of
after site sampling is completed. Contaminated gear will be double bagged and taken back
to the University of Reading where it will be disposed of as asbestos waste. Any other items
used to clean contaminated sampling kit will be disposed of in the same manner.
9 Quality Assurance/Quality Control
There are no specific quality assurance (QA) activities which apply to the implementation of
these procedures. However, the following QA procedures apply:
a) All data must be documented on field data sheets or within site logbooks.
b) All instrumentation must be operated in accordance with operating instructions as
supplied by the manufacturer, unless otherwise specified in the work plan.
Equipment checkout and calibration activities must occur prior to
sampling/operation, and they should be documented.
c) Random auditing during the sample collection process may take place to ensure
adherence to this SOP by steering group members.
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Appendix 2. Sample Survey Recording sheet
Sample identifier Date
Photograph file numbers of site surroundings
GPS reading
Notes on surrounding land
-land use
-proximity to roads/rail networks
-proximity to
residential/commercial/industrial areas
-description of any man made constructions on site
-any large flora (if this means moving sampling gird).
Ground conditions
Notes on any sampling modifications
Asbestos fragments present Yes/No
If yes
Description
Photograph file no.
Weight of sample (g)
Bagging
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details
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Appendix 3. Site audit reports
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Appendix 4 – Audits of Asbestos Analysis
Audit of asbestos in soil analysis at REC Ltd 8/12/2015 for the soils project
Main findings
1. The operational procedures need to be tweaked and updated to more accurately
reflect the procedure observed/audited for soil analysis and to remove some
processes that were not being used (e.g. sieves and pestle and mortar).
2. Overall the basics were good. Some further improvements to the method used could
be introduced to reduce the potential for cross-contamination between samples and
to ensure that the soil samples are fully dry before weighing.
3. More systematic examination of the tray sample could be undertaken if there was a
larger tray (or less sample) as this relies on visual analysis of a thin layer of soil. The
same applied for the stereo- microscopy examination in the Petri dish – i.e. a more
systematic technique for moving of a sub-samples from one side of the dish to the
other, to observe a relative thin layer of soil would optimise the likelihood of visual
detection of the asbestos if present.
4. The analyst correctly identified the asbestos types in the bulk sample they were
asked to examine during the visit.
Purpose and scope
The purpose of the audit was to check and assess the procedures used for the analysis of
asbestos in soils by REC Ltd (Manchester). All the soil samples from the project go through
this laboratory for the determination of the asbestos content. The procedures used were
observed and commented on in respect of systematic and random variations, and the
methodology set out in the operating procedures and how well they were followed. A test
sample was also used to assess the ability to identify the asbestos types present.
As a single analyst does all the samples for this project (another analyst is currently on
maternity leave) it was not relevant to look at any intra-laboratory (between analyst)
variations during this audit.
Description of analytical process used
The following current operational procedures (By Resource and Environmental Consultants
Ltd REC):
57
• Sample receipt, preparation and initial weighing (v 1.7 06/17/14);
• Quantification procedures:
o Stage 1 initial bulk analysis(V1.5 06/17/14);
o stage 2: Handpick and weigh of ACMS -coarse fraction ( V1.8 27/jul/2015);
o Stage 3 fibre counting and sizing by PCM-fine fraction (V1.7 29/Mar/2015).
Method of Auditing
The four OP’s above were used as the basis of the audit. A number of soil samples from
Reading had been received last Friday and the analysis of one of these samples was
observed and followed through the various stages.
A bulk test sample (a former AIMS PT) sample was also brought to site by the auditor for the
analyst to identify the asbestos types present.
Observations
Sample receipt, preparation and initial weighing (v 1.7 06/17/14)
1 The procedure is for samples between 0.25 to 1.5 Kg and gives a minimum drying
time of 12 hours at 40 oC (+ 5 oC) . – The procedure does not say, that the samples
should be dried completely before analysis. The samples are in a plastic tub and
covered with a permeable membrane in a drying cabinet and it is unlikely that 1 Kg of
material would be dry in 12 hours. This was recognised by the analyst who generally
leaves samples in for several days (Friday to Tuesday) in this case. However, no
data was available to assess when a constant weight was achieved using this drying
method. The drying time would also vary with soil types – (with clay soils taking
longer to dry) and the original soil moisture content. Weighing checks were good and
used calibration weights and balances which were maintained and checked by a
UKAS accredited service.
1a It was suggested that some experimental data be collected by reweighing the same
sample after a 24 drying period using the OP conditions for a number of days until an
approximate constant weight was achieved, to give a more accurate estimate of the
required drying time required.
1b A recommended minimum drying time should be specified based on the maximum
weight of soil received ~1.5 kg so that all the samples are likely to be dried to a near
constant weight , even though moisture content and soil type will differ between
samples.
58
1c As the current samples are weighed before and after drying – It might be helpful to
look at the past data to work out the moisture content removed from the samples, to
give further information on the typical moisture content of the soils received.
2 The OP uses a relatively low drying temperature (40 oC) to reduce the liberation of
VOCs. This is clearly a possibility at some brownfield sites where chemical
contamination is likely and use of an unventilated drying cabinet has to take this
approach – however, this will give prolonged drying times for the soils held a plastic
tub.
3 The procedure calls for brushing to be used to ensure the transfer of residual
materials. For a heavily contaminated sample, there is a possibility that some
asbestos will be transferred by the brush to a following sample, unless a new brush
or cleaning procedure is used.
3a Suggest the use of the brush could be avoided as only a small % of the sample may
not be transferred e.g. <0.01% and this is an acceptable weighing error – or that the
tub can be reweighed after transfer and this weight is deducted from the (container +
content after drying) weight to get an accurate dry weight of soil examined.
Stage 1 initial bulk analysis (V1.5 06/17/14);
4 This is broadly similar to the HSG 248 appendix 2 method for bulk analysis of a small
sample and has not been fully adapted to the needs of soil sample analysis and
could really be renamed as stage 2 to better follow the procedure used by the
analyst.
The first part of the procedures is used to examine the visible pieces of suspect
ACMs and to identify the type of asbestos present. This analysis was not observes
on the potential ACMs pieces extracted from the sample but a Bulk test sample was
given to the analyst to replicate the identification analysis.
The second part of the procedure is to search the soil sub-samples in the Petri
dishes produced by the coning and quartering technique and extracting small
bundles and pieces for identification of asbestos. None were found but the ID method
is the same as for the larger visible pieces above.
Stage 2: Handpick and weigh of ACMS -coarse fraction ( V1.8 27/jul/2015);
5 The soil samples are transferred into a shallow Teflon coated baking tray (~30 x 20
cm) where the material is examined and handpicked by eye in a HEPA filtered
59
cabinet. Small lumps were squeezed to assess if they were soil or solid (stones,
wood ACMs etc.) and places in two Petri dishes - one dish for Non-ACM solids and
one for potential ACMs. This was very much a hands-on examination lasting about 5
minutes. Coning and quartering then took place to produce a sub-sample in two
further Petri dishes. Materials placed in the potential ACM category Petri dish were
examined first by stereo microscopy, to assess whether they were ACMs.
5a The amount/depth of soil in the tray made is difficult to do a systematic assessment
of the soil by moving small sub-samples from one side of the tray to the other, so it
could be spread out in a thin layer for easier observation. The analyst can only see
the surface of the soil sample and needed more room to spread the sample out. This
could be more easily and reliably performed using a bigger tray (~ 40 x 30 cm) and a
scraper to spread the sub-sample. A tray with higher sides would also help to make
the coning and quartering a bit easier to do.
5b The coning and quartering was carried out in accordance with BSI methods.
5c Observation of potential visible ACMs was carried out in the stereo microscope. Here
experience is essential. No attempt to wash the soil from the lumps was made and it
should be considered whether some further cleaning (as necessary) may be put into
the OP. If the material examined was thought to be an ACM the stage 1 procedure
would be initiated after this stage to confirm that it was an ACM and identify the
asbestos type/s present.
5d No coarse fraction ACMs were found so it was not possible to observe weighing of
suspected ACMs or the use of the quantification worksheet to calculate the mass of
asbestos present.
Stage 3 fibre counting and sizing by PCM-fine fraction (V1.7 29/Mar/2015).
6 The Petri dish was further sub-sampled to weigh out ~ 1 g of soil into a smaller tared
Petri dish, the amount of soil added was recorded and then transferred into a 1 litre
conical flask – using a brush to wipe out the dish. 300 ml of water was added to the
flask. The flask was swirled for 20 seconds and a 1 ml aliquot withdrawn after 10 s
settling time and filtered onto a pre-wetted 0.8 um MCE filter and backing pad
support held in an air monitoring cowl. The liquid was drawn through the filter using a
syringe at the bottom of the pipe connection. The filter is then dried and mounted for
PCM analysis and quantification.
60
6a The final transfer to the conical flask involved the use of the brush and cross-
contamination is a possibility if brush is reused. The need to use a brush could be
avoided if the soil was weighed out directly into the flask which the water was added.
6b The re-use of the same filter holder was also a potential source of cross-
contamination and cleaning procedures need to be added and verified if non-
disposable equipment is used.
6c The filtration of a 1 ml aliquot is difficult to get a more even deposit and recommend
that a 5 ml aliquot of water should be added first to the funnel, before pipetting the 1
ml aliquot gently onto the surface – moving the pipette tip across the surface.
6d There was insufficient time to fully clear the filter so a previous sample filter (already
mounted and cleared) was chosen at random and examined. The filter was a good
mount but the deposit was slightly uneven across the slide (clusters of larger
particles) but there were no visible countable fibres and hardly any objects with a
>3:1 aspect ratio. A recount/quantification was not carried out as the original result
was BLQ and the auditors own observations showed that there was likely to be no
significant difference if a re-count/ quantification was performed.
6e Minor difference between the OP and the actual actions observed were noted (e.g.
use of 0.8 µm pore size filter and a longer drying time for the filter should be
specified).
Identification of asbestos in a bulk ACM sample
The analyst correctly identified the asbestos types in the bulk sample they were
asked to examine during the visit.
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Appendix 5 - Abbreviated Method Statement for Quantification of Asbestos in Soils by
REC Ltd
Sample Receipt, Preparation and Initial Weighing
Samples received for quantification of asbestos in soils were supplied in 1 l plastic tubs
clearly marked with a unique designation applied by the University of Reading. These
contained approximately 1 kg of soil. This allowed examination and any sub sampling
required to be conducted inside a HEPA equipped asbestos analysis cabinet. Sample
transport was arranged by in-house vehicles from Reading to the laboratory in
Manchester.
The sample weight was recorded as received.
The sample was then dried for a minimum of 48 hours in an oven operated at 40 +/- 5
0C. The mass of the sample was then determined and the dry weight calculated from a
knowledge of the mass of the empty container. The % moisture was then noted for
each sample.
Stage 1/2 – Initial Bulk Analysis
Stage 1 analysis identified whether suspected asbestos-containing materials (ACMs)
or fibres were present within the sample and then allowed identification of the type of
asbestos present.
Inside the HEPA-equipped cabinet the entire dried sample was transferred to a tray to
allow visual examination for the presence of any suspected ACMs or clumps of fibres.
Any such materials observed by the naked eye were removed and transferred to a
labelled container for further examination and weighing after removal of as much
extraneous material such as soil as possible.
A sub sample was then prepared by the coning and quartering technique. This aliquot
was transferred to two petri dishes to allow low power microscopic examination. This
examination step allowed detection of smaller pieces of ACMs or fibre clumps or
suspected asbestos fibres. These materials were removed for analysis and weighing.
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Suspected asbestos fibres were identified using polarised light microscopy (PLM) in
accordance with the procedures defined in HSE publication HSG 248 “Asbestos: The
analyst’s guide for sampling, analysis and clearance procedures”. This process was
accredited by UKAS to the ISO 17025:2005 Standard and all staff held the P401
qualification and many years’ experience.
Materials identified at this stage as asbestos-containing were weighed, and where the
product type was identified the tables contained within HSE publication HSG 264
”Asbestos: The survey Guide” were used to estimate the asbestos content of the
whole.
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Stage 3 – Fibre Counting and Sizing by Phase Contrast Microscopy (PCM) (Fine
Fraction)
Normally, only where Stage 1 analysis identifies loose asbestos fibres in the sample
would this third stage of analysis be performed. For the purposes of this work however
all samples were analysed using this third stage in the process.
A representative 1 g sub sample was taken from one of the petri dish sub-samples and
mixed in 300 ml of distilled water and agitated for 20 s. The solution was left to stand
for a further 10s before a 1ml aliquot was extracted from 1 cm below the surface using
a pipette. The aliquot was then deposited evenly onto a pre-wetted 25 mm 1.2 micron
nitro cellulose membrane gridded filter. Residual water was pulled through the filter
using a vacuum syringe and the filter was then dried on a hotplate or placed in an oven
at 40 +/- 5 0C for a minimum of 15 minutes and then mounted onto a slide. The
acetone/triacetin method was used to clear the filter in preparation for fibre
counting/sizing.
Each slide was examined by Phase Contrast Microscopy (PCM). Two hundred
graticule areas were examined and any fibres observed were counted. The number of
fields examined and fibres observed were counted using tally counters. The
dimensions of the counted fibres were also measured and recorded using a
quantification worksheet. The length of fibres was measured to the nearest 5 µm and
the width was measured to the nearest 0.5 µm.
Where prepared slides were found to be occluded and uncountable the solution would
be diluted by taking a 10 ml aliquot after shaking from the original suspension and
making up to 100 ml. This diluted sample would then be processed as the original and
the reported results would be corrected for the dilution. The solution would be diluted
further as necessary.
Stage 4 - further analysis
The above process represents the accredited method in place at REC Ltd, and was
validated to a reporting limit of 0.001% by analysis of replicate spikes in a number of
soils and hence obtaining data for the precision and bias of the method at that level. To
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improve the limit of detection and robustness of the method the decision was taken
prior to commencing this work to measure a further 9 x 1 ml aliquots of suspension as
per Stage 3. Note that the extension of the measurement to include ten separate
aliquots does not form part of the laboratory’s scope of accreditation. The summation
of the ten individual results and the associated improvement in statistical robustness
allows a reduction in reporting limit to 0.0001%. Note that this implies detection of, say,
three 5 micron length fibres on each of the ten filters on average to obtain this limit.
Quality Assurance and Control
The core of the work performed here is using the REC Ltd accredited method. As such
it is subject to a number of both internal and external quality assurance and control
measures.
These include,
Participation in the HSL’s “Asbestos in materials scheme” (AIMS), “Regular inter-
laboratory counting exchanges” (RICE) and “Asbestos in soils scheme” (AISS)
proficiency testing schemes. Individual’s performance in the AIMS and RICE schemes
are tracked based upon their performance scores issued by HSL. The analysts who
performed this work have maintained a classification of ‘0’ in the AIMS scheme and
have a majority of ‘A’ ratings for samples in the RICE scheme, with no worse than ‘B’
results whilst these samples have been analysed.
Routine analysis of in-house QC samples for identification, counting and soil analysis :-
as for the external scheme, the staff involved in this work maintained excellent
performance for the duration of this project.
Routine witness auditing of all staff performing the methods by the quality manager.
Audit findings, if any, result in corrective actions. There were no significant findings
during the performance of this work.
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In addition to this an external witnessing audit was conducted by Dr. Garry Burdett of
the Health and Safety Laboratory, Buxton, Derbyshire. There were no significant
findings in his report.
Routine monitoring of the environment in which these tests are performed for
background fibre counts.
The results obtained for the AISS scheme by the team in Manchester for the duration
of the project are listed in the table below. Note that one sample is submitted for
identification only and the other for both identification and quantification.
Round
Number
Sample
Number
Identification REC
Result (%)
Organiser
Spike
Value (%)
All labs range No. Labs
reporting
6 11 Crocidolite
12 Amosite 0.018 0.02 0.014-1.5 19
7 13 Amosite
14 Tremolite 0.043 0.05 0.0-0.44 28
8 15 Chrysotile
16 Crocidolite 0.059 0.03 0.016 -0.082 20
9 17 ** Non detect
18 Anthophylite 0.039 0.03 <0.0001 – 1.28 37