Asbestos in soil – respirable fibres in respirable dust – the missing link for risk assessment

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In recent years, the testing of soil for asbestos has become commonplace, often for purposes of risk assessment on brownfield sites.  The most common analysis for this purpose is presence and identification of asbestos, followed by quantification of the percentage mass of asbestos in the soil.

The problem with this approach is that percentage mass of asbestos does not directly relate to the risk posed.  As a simple example, 0.1% asbestos bound within an ACM, such as asbestos cement, presents a much lower immediate risk than 0.1 % of free fibres within the soil, as the risk to human health comes from airborne, respirable fibres.

One proposed solution to this problem (the fibre release test) is to agitate a dried soil sample, and carry out air tests under controlled conditions to try to estimate what the fibre release rate might be.  However, there are problems with this approach as well:

·         Collecting the dust as well as the fibres causes issues with identification and counting

·         It is difficult to standardise – different soil matrices may require different agitation periods, as do different asbestos types

·         Cleaning the equipment between samples is difficult

·         There are Health and Safety issues in deliberately creating an asbestos dust cloud

·         The lengthy duration of the test gives rise to unacceptable costs

Alternative methodology

Our solution is the Respirable Fibres in Respirable Dust test.   Dust monitoring focuses on PM10  concentrations - that is, the amount of particles with a diameters of less than 10µm. Therefore, a more useful test would be to calculate the possible asbestos concentration in this fraction of the sample, in terms of fibres per mg (f/mg PM10).   Effectively, we are able to carry out a test equivalent to the asbestos air test on the respirable portion of the soil.   This means that we can provide an estimate of three key indicators of risk that could not be calculated before:

1.     The fibres per ml of asbestos in air at a given level of dustiness (0.5 mg m3 for example)

2.     The dustiness level on site that would need to be reached before the clearance indicator of 0.01 f/ml would be breached

3.     The dustiness level on site that would need to be reached before the control limit of 0.1 f/ml would be breached.

The test is performed by measuring and counting the respirable asbestos fibres in the fines fraction of a soil sample.

Advantages of the method

·         The results provide a good indication of whether site activities are likely to give rise to airborne fibres, and to what levels

·         The results allow a decision to be made about the level of air monitoring that will be required, based on the requirements of the Control of Asbestos Regulations

·         The results allow informed decisions about dust suppression to be made

·         By removing factors that affect the release of fibres from soil, such as soil type, particle size and moisture content, the risk can be assessed more accurately

·         Cost – The test is significantly less expensive than the fibre release test, and can be scheduled as well as, or instead of, quantification.  Also, no extra equipment, and only minimal additional training would be required for laboratories already performing quantitative analysis.

·         This test eliminates the safety issues associated with deliberately agitating a dry sample that is known to contain asbestos, and with the cleaning of the equipment after each test.

The recent SOBRA (Society for Brownfield Risk Assessment) document on airborne asbestos fibre monitoring is of interest to work with this method – it discusses asbestos air testing and dust monitoring, and this test provides the missing link between the two:

http://www.sobra.org.uk/content/reports/Dust-Monitoring-Protocol-Earthwork-Activities-Brownfield-Sites.pdf

For further information, please contact  hazel.davidson@dets.co.uk

Hazel Davidson

Technical Marketing Manager

Derwentside Environmental Testing Services

www.dets.co.uk   or   info@dets.co.uk