Asbestos is an emotive topic, with the phrase ‘one fibre can kill’ often repeated, particularly by the more sensationalist press. In reality, asbestos is present in the air we breathe in most urban areas, with 0.015 fibres/ml as the clearance limit for buildings, and 0.1 fibres/cm3 as the Control limit for workplace exposure – when multiplied by the volume of air within a room or building, this is actually a not insignificant level.

However, it also depends on the type and size of fibre, the length of exposure, and the inherent susceptibility of the person as to whether an asbestos related respiratory disease may develop or not.

Asbestos consists of several different complex silicate minerals; for example, chrysotile (white asbestos) is Mg3Si2O5(OH)4, with the less common blue (crocidolite) and brown (amosite) forms considered to be more hazardous, but these forms are generally in low concentrations compared with chrysotile.

It is mined, not man made, and is fire resistant and therefore often used in insulating material. The word asbestos is derived from the Greek, meaning ‘unquenchable’, as they considered it could not be destroyed. It can, but only by heating to temperatures above 1,200° C, which will convert it to a silicate glass. It will not biodegrade, and remediation options are very limited – capping, vitrification or removal, for example – and require very careful consideration.

The link with respiratory diseases such as asbestosis, mesothelioma, bronchial carcinoma and pleural plaques, has been known for hundreds of years, and was conclusively proven in the 1930s, but it was not banned for industrial use until 1999.

The problem with the fibres is that they split easily, and form smaller and smaller fibres, which are then respirable, and can lodge in the lungs. Another issue is that diseases can remain latent for 15 – 40 years, so people are not aware until several years after the exposure has occurred. Asbestos is classified as a Category 1 carcinogen.

Asbestos risk in soil

The management of asbestos in the workplace, during demolition, and its assessment and removal, are all highly regulated by the CAR Regulations (2006), plus a wealth of other Health & Safety Executive (HSE) guidance documents. However, there is currently no specific code of practice or recent guideline document for asbestos in soil, or for its management during a site investigation.

For several years, many site operatives/consultants/developers have considered asbestos in soil to be of major concern only if high quantities are present, leading to its definition as hazardous waste (> 0.1%).

Another common misapprehension is that asbestos is not such an issue as long as soil is generally wet, and no airborne fibres are likely to be generated.

However, over the last 12 months or so, current thinking on asbestos in soil has changed to a very different scenario, due to a number of initiatives by various industry bodies, some of which are described in this article.

Asbestos in soil is a risk: as soil dries and dust is formed, it can then be airborne. It also adheres to shoes and vehicles, and is therefore carried to other locations, and disperses as it dries. Considering the widespread use of asbestos in construction, the number of buildings demolished on sites for redevelopment, and the disturbance and movement of soil during site investigations, remediation, and redevelopment, there is obviously cause for concern regarding the risks.

But how much of a risk, and at what concentration? Currently, there is no Soil Guideline Value (SGV) for asbestos, so operatives within the industry usually work to >0.1% for hazardous waste definition, and >0.001% for human health risk assessment.

The 0.1% value is taken from a document produced by the Interdepartmental Committee for the Redevelopment of Contaminated Land (ICRCL), 1990, Guidance note 64/85 ‘Asbestos on Contaminated Sites’, (but this does not take into account the 2006 regulations) and the 0.001% value is based on research conducted at the Institute of Occupational Medicine (IOM), 1988, Addison et al ‘The release of dispersed asbestos fibres from soils’.

This latter study involved drying soil, and generating dust, which was passed through filters to trap asbestos fibres for subsequent measurement. A soil containing 0.001% of asbestos fibres generated concentrations in air of >100,000 fibres/m3 where the total dust concentration was < 5mg/m3.

Recent High Court rulings have awarded damages based on a limited increase in probability of exposure to asbestos. In one case, a 17% increased risk was sufficient. This has caused significant concern within many industries – consultants, contractors, developers, landowners, laboratories – all of whom must take great care to ensure their staff, and future site users, are protected in order to avoid potential claims if personnel develop an asbestos related disease in the future. Asbestos related claims cost the insurance industry more than any other category.

Laboratory analysis

Due to the diversity of uses, asbestos containing material (ACM) can appear in many forms, such as asbestos cement (AC), asbestos insulation board (AIB), pipe lagging, gaskets, tiles, brake linings, rope and many others.

The proportion of asbestos in cement is generally between 10 – 15%, but the other materials may contain widely differing concentrations of asbestos. ACM can often be easily spotted visually in soils, but asbestos often exists as free fibres, which cannot be so easily detected.

Fibre length can vary significantly. Fibrous asbestos (FA) is usually friable – loose fibrous material that is often degraded and easily crumbles in the hand.

Asbestos fines (AF) are defined as free fibres, or fibre bundles, smaller than 7mm. It is the free fibres which present the greatest risk to human health, although very small fibres (< 5 microns in length) are not considered to be such a risk.

So what exactly do clients receive when they request an asbestos analysis from a laboratory? Unfortunately, at the moment, this situation is in a state of flux, and the level of analysis can vary greatly. It is imperative clients ascertain exactly which level of analysis is performed by the laboratory.

Currently, environmental laboratories offering asbestos in soil analysis can provide a variety of methods, some of which are accredited and some are not: 1 Gross visual screen, often performed as soils are mixed and weighed out for other analyses – this will only detect ACM – no quantification 2 Detailed screen using a x10 – x40 standard optical microscope – this will detect ACM and most free fibres – no quantification 3 Identification of asbestos type by Phase Contrast Optical Microscopy (PCOM) or Polarised Light Microscopy (PLM) – no quantification 4 Quantification by gravimetric measurement – visible pieces or large bundles are picked out manually and weighed – this will only detect ACM to 0.1% 5 Quantification by sedimentation and fibre measurement using PCOM or PLM (fibres) – this will detect fibres to 0.001% 6 Quantification and identification by Transmission Electron Microscopy – this is a high resolution method to 0.0001%, but the equipment is extremely expensive and only available in a very small number of laboratories

The United Kingdom Accreditation Service (UKAS), the accreditation body for laboratories, will not now accredit any new laboratories using methods 1 and 4 alone, as these are not considered either robust or fit for purpose. Over the next year or so, as UKAS perform their annual audits, laboratories currently accredited for these methods will have their accreditation withdrawn, unless they have submitted methods and validation for methods 2 and 5 as well.

In addition, in the future all asbestos analysis must be accredited, and laboratories will not be able to offer unaccredited methods for asbestos analysis.

However, if the gravimetric stage (as part of an accredited quantification method) gives a result of > 0.1%, then the material is classified as hazardous waste and this will be an accredited result. If the result from this stage is < 0.1%, this cannot be quoted as an accredited result, and the sample must proceed to the sedimentation method (method 5), in case free fibres constitute > 0.1%.

This is because the risk to human health is mostly from respirable fibres, not so much from the bound ACM, and therefore analytical methods must include the fibres.

ALcontrol Laboratories are accredited for methods 2, 3, and 5, so can offer a comprehensive asbestos service to their clients. Currently, only a small number of laboratories are accredited for Method 5 (which incorporates method 4).

These accredited methods are much more labour intensive and time consuming – an analyst can only perform three to four samples per day by the sedimentation method – than by the gravimetric method (30 to 40 per day). In addition, only a small proportion of the sample is actually analysed for Method 5, so the mixing and homogenisation of the initial soil is critical, and therefore takes longer. These factors are likely to impact significantly on costs for site investigation work.

Training staff can take many months, and they must pass the BOHS 401 certificate before they can be allowed to perform analyses unsupervised. Staff are also tested for colour blindness, and must perform regular Analytical Quality Control (AQC) samples to ensure ongoing competency. The laboratory must participate in a proficiency testing scheme, such as AIMS, and successfully identify pre-prepared blind samples.

The other problem is that only approximately 30% of soils sent to laboratories are requested for asbestos testing. ALcontrol provide a brief description of all received soils, and if the preparation laboratory staff suspect any further samples, these are scheduled for an asbestos screen (Method 2).

Approximately 20% of these samples are confirmed as containing asbestos. The worrying issue is what about the 60 to 70% of samples which are not tested at all? There are consultants who consider the risk of asbestos on a site can be predicted by the Conceptual Site Model (CSM), but it may be a rash decision to conclude this is certain enough, without any corroborative laboratory testing.

Guidelines in other countries

The Netherlands – RIVM 2009, soil remediation circular, states an intervention value of 0.01% in soil, and a study by Swartjes & Tromp, 2003, led to a tiered approach.

Tier 1 examines if one of the following criteria is met: • There is hardstanding • Greater than 0.5m of clean soil cover (and no excavation expected) • The site is covered by vegetation all year round • The asbestos is bound, non-friable, the ACM is not eroded, and is < 0.1% by mass

Tier 2 looks at the amount of respirable asbestos in the upper layers of soil, and also the indoor dust layers (if appropriate). A threshold of 0.001% is set for respirable fibres. Tier 3 looks at measurements of asbestos in air indoors and out – fibre concentrations in soil of 0.01% were only found to give background values in indoor dust.

Australia – The Australian Department of Health assume all forms of asbestos present a similar risk and define risk levels based on site use: • 0.001% asbestos FA and AF – all site uses • 0.01% asbestos for ACM – residential use, pre-schools, daycare centres • 0.04% asbestos for ACM – residential, minimal soil access • 0.02% asbestos for ACM – parks, open spaces, playing fields • 0.05% asbestos for ACM – commercial/industrial

USA – The US framework (2008) concluded no reliable method was available for predicting the concentration in air from a concentration in soil, given the complex interaction and number of variables. It also concluded that a reliable method for soil quantification could only achieve a limit of detection of < 0.25%.

They recommend a procedure to derive an action value for asbestos in air using a combination of soil, dust and air measurements, when the soil is vigorously disturbed, and monitoring the fibres collected on personal samplers. They do consider the limit of 0.001% may not be adequate. So although there are some areas of consensus, each country is taking a slightly different approach so far.

Industry action in the UK

Due to the increasing levels of concern within the industry, there are a number of initiatives aiming to improve the current situation:

• UKAS are guiding the laboratories by a process of improving and limiting the analyses which can be accredited. This will result in far more robust and defensible data

• The Environmental Industries Commission (EIC) has set up a working subgroup of their Laboratories Working Group to review the current situation and to raise awareness within the industry of the existing issues. They are organising a technical conference on November 1 at the Manchester conference centre, with experts from most concerned organisations such as the EA, Defra and the HSE. CL:AIRE (Contaminated Land: Applications in Real Environments) are organising this, and information can be obtained from the following link:

• The Health & Safety Laboratory are rewriting HSG 248 ‘The Analyst’s Guide’, to reflect the current changes in analysis, and this should be available for consultation by the middle of 2012

• The EIC have also conducted a survey, using Survey Monkey, on the current state of awareness within the industry, and more than 200 participants completed this. The data is currently being analysed, and will be available to EIC members

• CIRIA have funding for a project to develop client guidelines for compliance with current legislation and ‘Duty of Care’, and the Steering Group will be appointed by the end of September

• The Association of Geotechnical Specialists (AGS) have also set up a subgroup to discuss asbestos issues and liaise with the other industry groups • The Society of Brownfield Risk Assessment (SOBRA) are also discussing the issues and possible ways forward

• CL:AIRE are producing training modules for site staff

• The EA and Defra are aware of the concerns and are actively working with the industry groups, although there are no immediate plans to publish an SGV for asbestos

• There is an all party working group also looking at the problems, with a subgroup specifically considering the issue of low level asbestos in soil in primary schools


This is obviously an area of considerable uncertainty and increasing concern, and the various initiatives are generally welcomed by the industry. The downside will be increased costs – for the analysis itself, and also for taking more samples for analysis.

These costs are minimal, however, compared with the costs of not identifying asbestos on a site, and then for it to be discovered at a later date, and the potential claims that could ensue. Until some of these issues are resolved, and a Code of Practice is in place, all companies and staff should ensure they work to the ALARP principle (As Low

As Reasonably Practicable) with respect to exposure, and that some soils from every brownfield site are checked for asbestos. ?


Hazel Davidson, Technical Marketing Manager, ALcontrol Laboratories

Hazel Davidson has worked for ALcontrol Laboratories for 30 years, initially as an analyst, but then in a series of managerial roles. Special projects included the integration of several laboratory acquisitions, relocation of the laboratories from Chester to Hawarden, a Phare project in Bulgaria and Romania (implementing quality systems), and a UN project involving training for Iraqi environmental scientists in Jordan. Hazel participates on several industry committees (BSi, MCERTS, SCA and EIC), is a frequent speaker at conferences and runs several seminars each year for ALcontrol clients, as well as providing general technical support, both internally and externally.

Published: 10th Sep 2011 in AWE International