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VALIDATION TESTS ON MICROBIO AIR SAMPLERSgo to the Diagrams for this MicroBio Validation Report
Summary of Report of Tests on Bioaerosol Samplers
This summary prepared by Dr. F.W. Parrett ,
F.W. Parrett Limited, London SE9 2RA U.K.
Introduction: As part of the UK Department of Trade and Industry programme for the Validation of Analytical Methods (VAM), an experimental programme was undertaken with the following objectives:
The work described in this summary was carried out on behalf of the UK – Department of Trade and Industry, by AEA Technology PLC, Harwell, U.K. The full Report prepared by AEA Technology - is referenced as: AEAT-2382, October 1997, Procedures for the Development and Characterisation of Biological Particles: Final Report, NMSPU VAM Project 7: Particle Measurements: Project C
by W.D. Griffiths, I.W. Stewart, J.M. Clark, and I.L. Holwill.
This summary provides information only on the results of tests carried out on the performance of bioaerosol samplers. A full list of references including the publication of more detailed of the test programme is included at the end of this report summary.
Experimental Details: A Bioaerosol Test Chamber, designed by AEA Technology was used as the controlled environment, containing known concentrations of specific organisms under defined environmental conditions. The aerobiological samplers in the test programme were mounted inside the test chamber so they could be challenged with the same aerosol concentration. The test samplers were compared against a reference glass cyclone sampler, developed and used at AEA Technology (see references – Griffiths and Boysan, 1996)/.
The glass cyclone sampler draws air tangentially into the body of the cyclone along with a metered flow of sterile collection liquid. Airborne particles and collection liquid impact on the inside walls of the cyclone and wash down into a receiver at the bottom. The collection fluid is assayed for viable organisms.
Five commercially available bioaerosol samplers were included in the test programme:
Andersen Microbial Sampler (AMS). The version tested was the 6 stage cascade impactor. Particles are collected by impaction onto the nutrient agar surface of a series of petri dishes. Air flow is 28.3 litres/min with the largest particle sizes collected on the first stage and the smallest on the sixth stage.
Biotest RCS. Uses a centrifugal fan around which a rectangular plastic strip holding nutrient agar is mounted. Air flow from the fan causes impaction of particles onto the agar surface. Flow rate is not easy to evaluate but the manufacturer's value of 40 litres/min was assumed.
Biotest RCS Plus. A later version of the Biotest RCS, of where the design allows more accurate determination of the air flow rate. The sampler can be set to sample fixed volumes from 1 to 1000 litres at 50 litres/min.
MicroBio MB1 PLUS. This is an up to date version of a single stage sieve impactor. Air at a flow rate of 100 litres/min passes though metal cover (a 220 hole sieve plate) under which is mounted a nutrient agar contact plate (55mm diameter). The volume sampled can be set from 33 to 500 litres.
MicroBio MB2. A more recent model of the MicroBio series, which samples up to 1000 litres of air at 100 litres/min. The sampling system is the same as the MicroBio MB1 PLUS.
Microorganisms used. Tests were conducted with S.cerevisiae cells (a yeast), and with P.expansum spores (a fungi).
With P.expansum spores tests were carried out with the test samplers in two orientations - inlets facing the downward flow of air, and also with inlets at right angles to the flow of air. Tests were carried out at 60% R.H. and 20 deg.C.
With S.cerevisiae tests were made only with the inlets facing the downward flow of air, but comparative experiments were carried out at 30% and 70% R.H. at 20 deg.C.
Volumes of air sampled were selected to give convenient numbers of colonies on the nutrient agar plates and strips.
Results:
S.cerevisiae cells. At 30% R.H. there is no significant difference between the performance of the cyclone sampler and that of the AMS, but both are significantly higher than the RCS and RCS+ and the MB1. At 70% R.H. there is no significant difference between the cyclone, AMS, MB1 and MB2, but these four are significantly higher than the RCS and RCS+. The results are summarised in Figures 1 and 2.
P.expansum Spores. In the Bioaerosol Test Chamber the test samplers gave significantly higher mean values for bioaerosol concentrations than the reference glass cyclone. With this particular organism this may be due to the use of Milli-Q water as the collection fluid in the cyclone sampler, which may have damaged the spores more than impacting them directly onto nutrient agar, as with the test samplers. With the AMS and the MB1 the mean ratios for collection are significantly lower with the inlets at right angles to the air flow. With the RCS+ and MB2 there is no significant difference in the means at the two different orientations. The results are summarised in Figures 3 and 4.
Conclusions: The results from this study showed that the Andersen Microbial Sampler, The MicroBio MB1 and MicroBio MB2 gave comparable ratios of experimental to expected airborne concentration to the cyclone sampler when sampling S.cerevisiae cells. With P.expansum spores the Andersen Microbial Sampler and the MicroBio MB1 and MB2 gave higher ratios of experimental to expected airborne concentration than the cyclone sampler. The orientation of the test sampler inlets made no significant difference to the results. The study has demonstrated that the cyclone sampler, the Andersen Microbial Sampler, the MicroBio MB1 and the MicroBio MB2 meet the basic criteria for a suitable reference sampler. It will be important to investigate how well they perform under "real life" challenge conditions.
Publications: Results of this study have been presented as papers at conferences of The Aerosol Society (University of Warwick, March 1997), and the Bioaerosol Conference of the Society of Chemical Industry, London, October 1997. Fuller details of the results has been published in J. Aerosol Science, Vol 30, No.8, pp 1029-1040 (1999).
References:
Griffiths, W.D. and Boysan, F. (1996) " Computational Fluid Dynamics (CFD) and Empirical Modelling of the Performance of a Number of Cyclone Samplers", J. Aerosol Science, 27 (2), 281-304.
Stewart, I.W., Griffiths, W.D. and Futter, S.J. (1997) "Development and Characterisation of Biological Particles and Bioaerosol Standards". Proc. 11th Annual Conf. of The Aerosol Society, University of Warwick, March 1997, pp. 18-23.
Clark, J.M., Futter, S.J., Griffiths, W.D., Holwill, I.L. and Stewart, I.W. (1997) "Effects of Environmental Conditions on the Survival of Industrially relevant Airborne Microorganisms". Proc. 11th Annual Conf. of The Aerosol Society, University of Warwick, March 1997, pp. 24-29.
Stewart, I.W. and Griffiths, W.D. (1998) "Characterisation of Bioaerosol Samplers Commonly Used by the UK Biotechnology Industry". Submitted to the 5th International Aerosol Conference, Edinburgh, 12 - 18 August 1998. In press J. Aerosol Sci.
Griffiths, W.D. and Stewart, I.W.(1998) "The Effect of Aerosolisation Parameters and Additives on Bioaerosol Viability". Submitted to the 5th International Aerosol Conference, Edinburgh, 12 - 18 August 1998. In press J. Aerosol Sci.
Griffiths, W.D., Stewart, I.W., Clark, J.M. and Holwill, I.L. (1998) "The Effects of Environmental Factors on Bioaerosols". Submitted to the 5th International Aerosol Conference, Edinburgh, 12 - 18 August 1998. In press J. Aerosol Sci.
Griffiths, W.D. and Stewart, I.W. (1999) "Performance of Bioaerosol SAMPLERS Used by the UK Biotechnology Industry". J. Aerosol Science, Vol 30, No.8, pp 1029-1040 (1999).