Capping asbestos-laden soils may not be the safest solution to prevent the risk of future exposure, according to the findings of a new study. The research implies a greater level of risk than previously assumed at many former sites where either asbestos was used in production or the buildings themselves were constructed with asbestos insulation.

The Health and Safety Executive say there could still be around half a million commercial and private properties containing four million tons of hidden asbestos material, including asbestos-contaminated soil. It is estimated that more than over half of all Britain’s residential development occurs on asbestos-contaminated land at the former sites of factories, foundries, mills and engineering workshops.

It’s not just the sites of former factory premises with possible asbestos-contaminated soil. In a number of cases, insufficient asbestos awareness or non-compliance with asbestos disposal regulations has led to soil contamination long after a site has been landscaped over to create a new development or parkland amenity. The amount of hidden asbestos is regularly reported when residents living nearby to a landfill site become concerned over lorries transporting waste, which they discover includes asbestos materials.

The health risk may now be even greater than previously thought. The long-held belief that asbestos fibres cannot move through soil is being challenged by the results of a new ‘soil sampling’ technique carried out by US scientists.

It may not be enough to only sample contaminated material

Research teams from the Universities of California and Pennsylvania have used a method developed in 2013 called ‘activity-based sampling’. The technique mimics likely activities at a site and monitors air in the ‘breathing zone’ to determine the concentration of asbestos fibres.

The results show that soil containing dissolved organic matter sticks to asbestos particles. This causes a change to the electric charge on the outside of the particle, which allows it to easily move through the soil. The researchers suggest that it may not be enough to only sample the contaminated material. There are a number of other factors that need to be considered when assessing the likelihood of the fibre particles getting into the air, such as  fibre type, local weather and the kind of activities regularly taking place in the site area.

It could mean that simply walking on contaminated soil would be enough to stir up the fibres just below the surface of the ground. Over an extended period of time, a regular walk through a normal-looking, but in reality, an asbestos-contaminated area could cause a health risk. Airborne microscopic fibre particles could be breathed in, which may eventually lead to asbestos-related conditions, such as asbestosis or the incurable mesothelioma cancer of the lung linings.

Method for determining ‘trace’ amounts of asbestos in materials

In 2013, the HSE, together with the Environment Agency (EA) issued a Joint Statement, which included recommendations to develop guidance support in the remediation of asbestos in soil, made ground and construction and demolition materials, according to the requirements of the Environmental Permitting Regulations 2010. In addition, guidance or, if necessary, regulated enforcement was to be developed involving the presence of asbestos and/or asbestos-containing materials in construction and demolition materials as a consequence of the failure to remove asbestos from buildings and/or structures prior to demolition.

The statement also recommends the method to be used by analysts in the UK for determining ‘trace’ amounts of asbestos in materials, as set out in the Health & Safety Guide, HSG 248.

A submitted soil sample is quantified in three stages, from (i) initial bulk analyses, (ii) hand-picked sampling, which must be between 200g and 1kg (coning and quartering) to (iii) analyses by Polarised Light Microscopy (PLM), which provides information on the absorption colour and optical path boundaries between minerals of differing refractive indices.

Minimum of two samples at high magnification

Currently, HSG 248 recommends that ‘asbestos not detected’ should be reported when no fibres are found in a sample after 10 minutes careful search under a stereo microscope. A minimum of two more sample preparations are mounted in suitable Refractive Index (RI) Liquid at high magnification for a further 5 minutes under PLM or PCM (Phase Contrast Microscopy) to quickly find larger fibres.

It is suggested that if only 1 or 2 fibres are detected and identified as asbestos, the term ‘trace asbestos identified’ should be applied. Under the Control of Asbestos Regulations 2006/12, any mixture that contains one or more of the six types of asbestos fibres at more than trace amounts, as defined in HSG248, falls within the legal definition of asbestos.

The United Kingdom Accreditation Service (UKAS) previously reported that the testing of soils for asbestos had become the most regulated type of testing a laboratory can provide to the contaminated land sector. Around 1.8 million people are exposed to asbestos every year in the UK, according to the HSE. Many of the most vulnerable to exposure are known to be building contractors, tradesmen and ground clearance crews who work on the redevelopment of former asbestos-using sites.