The release of dispersed asbestos fibres from soils

Both natural and industrial asbestos contamination in soil on sites required for development can present health hazards if the soil is to be disturbed. Very little information is available about likely airborne asbestos fibre concentrations which might be encountered in working such a site or on the possible suppressant effects of water spraying during work. This study is aimed at providing some basicrelevant information to these problems. Artificial mixtures were prepared using three different soil types (clay, sand and intermediate) with each of three asbestos types (chrysotile, amosite and crocidolite)in concentrations of 1%, 0.1%, 0.01% and 0.001%, by weight.Airborne dust clouds were generated over periods of four hours from each mixture using a dust dispenser discharging into a 1.3 m3 test chamber. Airborne dust concentrations were measured for the full duration of the test using gravimetric dust sampling instruments and a sequence of membrane filter samples were collected for fibre counting by phase contrast optical microscopy. Airborne fibre concentrations were determined for each test as time weighted averages and these were compared to the average respirable dust concentration in the normalised fibre concentration (f ml-1/mg m-3) which allows the airborne fibre concentration to be related to common occupational exposure limits such as that for nuisance dust at 5 mg m-3. Parallel tests were carried out using transient dust clouds generated from each mixture with progressive controlled addition of water. Airborne fibre concentrations measured over fixed time periods after initial dust cloud generation were used to compare the effects of the addition of water to the soils.The results showed that airborne fibre concentrations could be very high (> 20 f ml-1) and even 0.001% of asbestos in a dry loose mixture was capable of producing airborne respirable asbestos concentrations in excess of the 0.01 f ml-1 clearance limit while at the same time the respirable dust concentration remained below the nuisance dust OEL of 5 mg m-3. The major controlling factor on airborne fibre levels was the amount of asbestos in the mixtures, although the nature of the soil and the asbestos type had some influence. For example, loose sandy soils and soils containing amphibole asbestos tended to produce higher fibre concentrations (when disturbed) than clay soils or soils with chrysotile. The addition of water to the soils greatly reduced the airborne fibre concentrations. “”