IMPACTION ONTO A GLASS SLIDE OR AGAR VERSUS IMPINGEMENT INTO A LIQUIDFOR THE COLLECTION AND RECOVERY OF AIRBORNE MICROORGANISMS

To study impaction versus impingement for the collection and recovery of viable airborne microorganisms, three new bioaerosol samplers have been designed and built. They differ from each other by the medium ont o which the bioaerosol particles are collected (glass, agar, and liqui d) but have the same inlet and collection geometries and the same samp ling flow rate. The bioaerosol concentrations recorded by three differ ent collection techniques have been compared with each other: impactio n onto a glass slide, impaction onto an agar medium, and impingement i nto a liquid. It was found that the particle collection efficiency of agar slide impaction depends on the concentration of agar in the colle ction medium and on the sampling time, when samples are collected on a nonmoving agar slide. Impingement into a liquid showed anomalous beha vior with respect to the sampling flow rate. Optimal sampling conditio ns in which all three new samplers exhibit the same overall sampling e fficiency for nonbiological particles have been established. Inlet and collection efficiencies of about 100% have been achieved for all thre e devices at a sampling flow rate of 10 liters/min. The new agar slide impactor and the new impinger were then used to study the biological factors affecting the overall sampling efficiency. Laboratory experime nts on the total recovery of a typical environmental microorganism, Ps eudomonas fluorescens ATCC 13525, showed that both sampling methods, i mpaction and impingement, provided essentially the same total recovery when relatively nonstressed microorganisms were sampled under optimal sampling conditions. Comparison tests of the newly developed bioaeros ol samplers with those commercially available showed that the incorpor ation of our research findings into the design of the new samplers yie lds better performance data than data from currently available sampler s.