The release of dispersed asbestos from soil.
J Addison, LST Davies, A Robertson, RJ Willey Institute of Occupational Medicine Glasgow College of Tech...
J Addison, LST Davies, A Robertson, RJ Willey Institute of Occupational Medicine Glasgow College of Technology John Addison Consultancy Ltd
Reasons for research
Department of the Environment needed to provide practical advice to those companies involved in major land rehabilitation projects as to the level of asbestos that might not constitute a serious risk to the health of later site workers if it were left on the site, even
if they were unaware of its existence.
Project Aims
Is there a level of asbestos contamination in soil such that no action is required to continue work of decontamination? Is there a level of contamination of asbestos in soil such that the risks of work on the site are tolerable?
Assumptions
Asbestos can be detected by PLM at concentrations that may not constitute a serious risk when disturbed. Workplace controls will limit dust exposures to 4 mg.m-3 (previously 5) Worst case scenario – dry conditions.
Materials
3 soil types: sand, clay, intermediate 3 asbestos types: chrysotile, amosite, crocidolite 4 concentrations: 1%, 0.1%, 0.01%, 0.001% by mass in bulk soils. 36 mixtures in total.
Dust Generation
1.5 m3 test chamber Airborne dust generated at 5mg.m-3 using Timbrell dust generator for four hours Respirable and total dust samples collected for whole duration Short term sequential membrane filter samples collected for whole time
Fibre Counting
Membrane filters counted for asbestos concentration; cumulative counts summed for average asbestos concentration. Counting rules same as WHO Asbestos concentrations normalised to respirable dust concentration Expressed as f.ml-1/mg.m-3
Average airborne fibre concentrations f.ml-1 Conc. of asb. in Soil
0.001%
0.01%
0.10%
1%
Chrysotile Amosite Crocidolite
0.06 0.1 0.17
0.18 0.4 0.67
0.98 1.15 1.43
6.1 12.6 13.8
Clay Intermediate Sand
0.13 0.12 0.07
0.17 0.49 0.59
0.74 0.71 2.11
6.6 10.1 15.9
Overall averages
0.11
0.41
1.19
10.8
Normalised fibre concentrations; averages for each asbestos type in all soils, and each soil type for all asbestos types Conc. of asb. in Soil
0.001%
0.01%
0.10%
1%
Chrysotile Amosite Crocidolite
0.01 0.03 0.03
0.04 0.07 0.15
0.16 0.21 0.28
1.34 2.0 2.5
Clay Intermediate Sand
0.02 0.03 0.02
0.02 0.11 0.13
0.11 0.15 0.38
0.85 2.1 2.93
Overall Mean
0.02
0.1
0.21
1.96
10
3
(f/ml/mg/m )
Normalised asbestos fibre conc.
Average Conc. for all soil types and all asbestos types
1
0.1
0.01 0.001
0.010
0.100
Bulk asbestos mass %
1.000
IOM results: averages for each asbestos type in all soil types
IOM results: averages for all asbestos types in each soil type
Normalised asbestos fibre conc.
10
Clay Intermediate
1
Sand
0.1
0.01 0.001
0.01
0.1
Bulk asbestos mass %
1
First Conclusions
Asbestos type is a factor Soil type is a factor 0.001% asbestos content can give airborne fibre concentrations greater than the control limit if dust is generated at concentrations of around 5 mg.m-3 A “safe” level would be below 0.001% BUT…………..
Effects of Moisture Content
36 mixtures tested dry and wet Water content added progressively up to 50% by weight Pellets of mixtures blasted into dust chamber Sampling on to membrane filters after 30 minutes Fibre counting as before; dust measurements for dry soils only
GCT results: Normalised fibre conc. for each asbestos in each dry soil, f.ml-1/mg.m-3 Soil Type Clay
% in bulk Chrysotile Amosite Crocidolite Average Intermediate Chrysotile Amosite Crocidolite Average Sand Chrysotile Amosite Crocidolite Average
Average fibre conc. for all soil types and all asbestos types: IOM Tests; GCT Tests Normalised asbestos fibre 3 conc. (f/ml/mg/m )
10
1
0.1
0.01 0.001
0.010
0.100
Bulk asbestos mass %
1.000
Normalised airborne fibre conc.
GCT: averages for each asbestos type in all soils 10.00
Chrysotile Amosite Crocidolite 1.00
0.10
0.01 0.001
0.01
0.1
Bulk asbestos mass %
1
GCT: Averages for all asbestos types in each soil
Normalised airborne fibre conc.
10.00 in clay in Interm in sand 1.00
0.10
0.01 0.001
0.010
0.100
Bulk asbestos mass %
1.000
Fibre concentrations declining with increased water content . All asbestos contents 1%.
Normalised airborne fibre conc.
100.00 Amosite/Inter Amosite/Sand
10.00
Crocidolite/Clay 1.00 0.10 0.01 0.00 0
10
20
30
Water content % by weight
40
50
Second conclusions
Water has a strong suppressant effect on the release of asbestos during disturbance Even 5% water content had a major effect, reducing risks to a tolerable level for all but 1% mixtures 5% water content is the normal minimum for most soils in Europe even after dry periods Dry disturbance would still be a problem at 0.001%
Quantitative Bulk Method
Development and validation of an analytical method to determine the amount of asbestos in soils and loose aggregates LST Davies, GZ Wetherall, C McIntosh, C McGonagle, J Addison Institute of Occupational Medicine HSE Contract No: 2491/R42.46 DoE Contract No: PECD 7/10/234
Quantitative analysis by PCM/PLM
Method developed for DoE and HSE Identify asbestos by PLM Aqueous suspension of 1 g in 250ml 1, 2, 5 ml aliquots on membrane filter PCM fibre count & fibre dimension estimates Fibre volume calculation : mass content
Method validation: IOM
Two experienced fibre counter analysts No special training 30 different mixtures of asbestos in soil and other minerals 143 filter preparations 457 fibre counts & mass estimates
1.00E+01
1.00E+00
O b s M ass % A n alyst I
1.00E-01
1.00E-02
1.00E-03
1.00E-04
1.00E-05
1.00E-06 1.00E+01
1.00E+00
1.00E-01
1.00E-02
1.00E-03
1.00E-04
1.00E-05
1.00E-06
Obs Mass% Analyst G
Ratio of Observed Mass % to True Mass % 10
1
0.1
0.01 0.0001
0.0010
0.0100 True Mass %
0.1000
1.0000
1.00E-06
O bserved M ass % O p.G
1.00E-05
1.00E-04
1.00E-03
1.00E-02
1.00E-01
1.00E+00
1.00E+01 1.00E+00
1.00E-01
1.00E-02
True Mass %
1.00E-03
1.00E-04
Conclusions I
Accuracy and precision good enough at 0.1% and 0.01% and adequate at 0.001% Systematic differences between analysts can be reduced by training Asbestos type and grade had significant effect Matrix had significant effect
Conclusions II
Fibre numbers not a good estimate of bulk mass content Large fibres increase bias PLM/PCM discrimination is effective Provided useful results at a real site; NDs by PLM gave results of 0.001% or less
Risk Assessment
Airborne fibre concentration can be expressed as an exponential function Y=M+A+S+C M= concentration at the 0.001% asbestos concentration A = the effect from the asbestos type S = the effect of the soil type C = the effect of the asbestos content of the soil
Exponential factors from Log=linear regression Conc = Exp(M + A + S + C) M = Y axis intercept
2.534
Asbestos Type A
Asbestos content C Soil Type
0.001%
0.0
S
Amosite
0.0
Clay
0.0
0.01%
1.34
Chrysotile
-0.61
Interm.
0.35
0.1%
2.38
Crocidolite
0.13
Sand
0.84
1%
4.57
Predicted fibre concentrations Amosite
Sand
Interm.
Clay
0.001%
0.18
0.11
0.08
0.01%
0.70
0.43
0.30
0.10%
1.99
1.22
0.86
1.00%
17.74
10.87
7.66
Further development
Schneider T, Davies LST, Burdett G, (1998) Development of a method for the determination of low contents of asbestos fibre in bulk material. Analyst; 123:1393-400
