Round-robin assay of mould detection on filters contaminated artificially in a dust tunnel

Status:

completed 02/2000

Aims:

Round-robin assays are a routine measure for external quality assurance in analytical laboratories. The BG Institute for Occupational Safety - BIA performs round-robin assays on behalf of the Committee for Biological Agents (ABAS), in order to measure the concentration of micro-organisms and microbial compounds in workplace atmospheres. The purpose of these round-robin assays is to provide the in-company metrology departments or external laboratories commissioned by them with a means of documenting their quality by way of external quality assurance measures.

Activities/Methods:

Common sampling was performed on-site and actual samples tested in 1997 in an initial round-robin assay performed for measurement of the concentration of mould fungus in air samples. Conversely, in the round-robin assay performed in the Autumn of 1999, participants were supplied with filters with a defined spore concentration produced under largely standardized conditions. Sampling by the participants themselves was thus excluded from the assay. The focus of testing lay upon analysis of the samples in the laboratory. Mixed pore suspensions were produced in three different concentrations (low: < 1,000 CFU/m³, medium: 10,000-100,000 CFU/m³, high: 200,000-1,000,000 CFU/m³) from fresh cultures of two different Penicillium species. The pore suspensions were then atomized by means of a hydropneumatic nozzle atomizer. 24 PGP-GSP heads, mounted on a frame and directed into the air flow, were employed for sampling. The filter throughput was 5.8 l/min. Each filter was treated with 174 l of fungal spore aerosol over a sampling duration of 30 minutes. 18 sample measurement series were performed, the series being repeated with the same three spore aerosol concentrations (see above). For organizational reasons, all filters were treated on two successive days. Each participant was supplied with nine samples on gelatine and nine on polycarbonate filters. The samples were to be analysed in accordance with the method specified in the Technical Rules for Biological Agents (TRBA 430). Treated filters with low spore concentrations were to be analysed by the direct method, those with medium and high concentrations by the indirect method.

Results:

The reference data obtained during preparation of the filters reveal distributions of varying magnitude on the two filter types (gelatine, polycarbonate), both within the various concentrations (low, medium, high) and between the two days on which treatment was performed. The strongest variations were observed on the lowest concentrations. Since evaluation by way of the direct method of the filters prepared with this magnitude of spore concentrations presents only minor potential for error, and was obviously well under control in all laboratories, conformity of the results was satisfactory. For the filters evaluated by means of the indirect method (medium and high concentration), on the other hand, results were obtained which were both too high and too low. Differences were observed here between the distributions following preparation of the filters and the participants' results which can be attributed to the more complex analysis method. Since the potential variation between the filters prepared in the dust tunnel was relatively high, the BIA is to develop a new procedure more suited to defined preparation of filters in the laboratory. A further round-robin assay is to be performed when the test phase of this measure has been completed.

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