Determination of the soluble portion of dust

Status:

completed 12/2004

Aims:

The general dust limit value for the respirable and inhalable dust fractions constitutes elementary limit values for assessment of the exposure to dust at workplaces. The scope of this limit value extends to poorly soluble and insoluble dusts. A definition of the soluble portion of dusts or specifications for an analysis method for determination of the soluble component of dusts do not exist. A convention method was to be developed which was to be straightforward and suitable for application in practice with justifiable use of resources.

Activities/Methods:

The soluble component of dusts is to be measured directly on filter samples taken from working areas. The dust mass collected by the filter is first measured by weighing. The filter is then placed in a filtration facility and covered with the solvent. After leaving it for a defined duration, the solvent is drawn off through the filter by a vacuum pump. The residual insoluble or poorly soluble dust portion can then be determined by weighing. A special filtration facility first had to be designed into which the filter with the sampled dust could be inserted. The filtration facility provides adequate space above the filter for covering with a solvent. The arrangement ensures that the solvent reaches the entire area of the filter coated with dust. The test series were limited to respirable dusts deposited on membrane filters. For this purpose, ground samples of typical easily or relatively easily soluble materials were selected (calcite, dolomite, gypsum, semihydrate, anhydrite, wollastonite). The tests were conducted with three different solvents (deionized water, 0.1n hydrochloric acid, pH 7 buffer solution).

Results:

As preliminary result a convention method was developed for measurement of the soluble dust portion in air samples. Deionized water is employed as the solvent. The method has been developed to date for filters in the PM 4F sampling system (filter diameter 70 mm, cellulose nitrate filters, respirable dust fraction). The method can be transferred in principle to other sampling systems with other filter sizes. The soluble portion is measured directly on the filters with sampled dust themselves, which are fitted into a special filtration facility following measurement of the dust mass, and coated twice for half an hour each time with the solvent, which is stirred during the process. Following drying, the filters are weighed again and the soluble portion and remaining poorly soluble/insoluble component thus determined. The convention method is to be employed in order to gather sample data on the solubility of dust in the respirable fraction for a range of working areas. The results will be collected and evaluated in order to enable recommendations to be issued regarding the areas in which it may prove necessary in future to determine the soluble portion.

Further informations:

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