Medical Applications of Dust-free Rooms. III. Use in an Animal Care Laboratory

Bacterial air sampling in an animal care laboratory showed that dense aerosols are generated during cage changing and cage cleaning. Reyniers and Andersen sampling showed that the airborne bacteria numbered 50 to 200 colony-forming units (CFU)/ft³ of air. Of the viable particles collected by Andersen samplers, 78.5% were larger than 5.5 μm. A low velocity laminar air flow system composed of high-efficiency particulate air (HEPA) filters and a ceiling distribution system maintained the number of airborne viable particles at low levels, generally less than 2 CFU/ft³. Vertical air flow of 15 ft/min significantly reduced the rate of airborne infection by a strain of Proteus mirabilis. Other factors shown to influence airborne infection included type of cage utilized, the use of bedding, the distance between cages, and the number of animals per cage.     

Energy from vascular plant wastewater treatment systems

Water hyacinth (Eichhornia crassipes), duckweed (Spirodela sp. andLemna sp.), water pennywort (Hydrocotyle ranunculoides), and kudzu (Pueraria lobata) were anaerobically fermented using an anaerobic filter technique that reduced the total digestion time from 90 d to an average of 23 d and produced 0.14-0.22 m³ CH₄/kg (dry weight) (2.3-3.6 ft³/lb) from mature filters for the 3 aquatic species. Kudzu required an average digestion time of 33 d and produced an average of 0.21 m³ CH₄/kg (dry weight) (3.4 ft³/lb). The anaerobic filter provided a large surface area for the anaerobic bacteria to establish and maintain an optimal balance of facultative, acid-forming, and methane-producing bacteria. Consequently the efficiency of the process was greatly improved over prior batch fermentations.     

Air Filters for Germ-free Isolators

A germ-free isolator must have a perfect bacterial filter. This paper describes a new, relatively inexpensive, stainless-steel filter frame, which is easily and quickly assembled and protects the enclosed filter material at all times. Resistance to the flow of air was less than 4 inches of water at an airflow of 30 ft³/min through the filter frame with 204 inches² of surface area and four, one-half inch thick pieces of fiberglass filter material. This filter performed satisfactorily in our gnotobiotic laboratory and was found to be consistently 100% efficient in removing an aerosol containing Serratia marcescens from an air stream under a variety of operating conditions.     

Reaerosolization of Fluidized Spores in Ventilation Systems

This project examined dry, fluidized spore reaerosolization in a heating, ventilating, and air conditioning duct system. Experiments using spores of Bacillus atrophaeus, a nonpathogenic surrogate for Bacillus anthracis, were conducted to delineate the extent of spore reaerosolization behavior under normal indoor airflow conditions. Short-term (five air-volume exchanges), long-term (up to 21,000 air-volume exchanges), and cycled (on-off) reaerosolization tests were conducted using two common duct materials. Spores were released into the test apparatus in turbulent airflow (Reynolds number, 26,000). After the initial pulse of spores (approximately 10¹⁰ to 10¹¹ viable spores) was released, high-efficiency particulate air filters were added to the air intake. Airflow was again used to perturb the spores that had previously deposited onto the duct. Resuspension rates on both steel and plastic duct materials were between 10⁻³ and 10⁻⁵ per second, which decreased to 10 times less than initial rates within 30 min. Pulsed flow caused an initial spike in spore resuspension concentration that rapidly decreased. The resuspension rates were greater than those predicted by resuspension models for contamination in the environment, a result attributed to surface roughness differences. There was no difference between spore reaerosolization from metal and that from plastic duct surfaces over 5 hours of constant airflow. The spores that deposited onto the duct remained a persistent source of contamination over a period of several hours.     

Assessment of counting efficiencies for labeled protein and other macromolecules in filter disk assays

A several-fold greater counting efficiency is observed for protein labeled with [³H]leucine than for free [³H]leucine using a conventional filter disk assay. A similar, though less marked, effect is noted for ¹⁴C-labeled molecules. These results are comparable to those reported by others for counting efficiencies of labeled DNA and deoxynucleotides and illustrate the generality of this effect with regard to macromolecules and their low-molecular weight precursors. This phenomenon, presumably due to differences in the distribution of large and small molecules within filters, gives rise to errors in the quantitation of macromolecule synthesis if a counting efficiency identical to that of the precursor is assumed to apply. A convenient method for determining counting efficiencies of various molecules bound to filters is presented which eliminates this problem.     

Monitoring of the toxic dinoflagellate Karenia brevis using gyroxanthin-based detection methods

The threat to human health and fisheries resources due to blooms of the toxic dinoflagellate Karenia brevis has lead to widespread public concern and calls for continuous monitoring of coastal waters for this organism. Here, a rapid and sensitive photopigment-based monitoring approach is described that incorporates refinements to standard filtration and analytical methods. This method uses the biomarker pigment gyroxanthin-diester contained in cells of some gymnodiniod species including K. brevis. Investigations of the retention efficiencies of five filter types for gyroxanthin from natural blooms of K. brevis showed no significant differences between GF/F, GF/C, 934-AH, GF/A or GF/D filters. Retention efficiencies were generally greater than 98% of cells added, indicating that the larger nominal pore size filters may be used safely for sample collection, reducing overall filtration times for large volumes of water. Simulated bloom experiments using cultures of K. brevis added to unfiltered water from Galveston Bay showed that retention of gyroxanthin on GF/D filters was significantly lower than on other filter types. There were significant interactions (p < 0.01) between filter type and cell density for the variables gyroxanthin, gyroxanthin chl a^–1 and gyroxanthin cell^–1, suggesting that the performance of the different filter types was dependent on cell density. Retention efficiencies for the simulated blooms ranged between >99% of cells retained and <30% of cells retained (greatest losses were for the GF/D filters). Combined results of natural and simulated blooms indicated that GF/C, 934-AH or GF/A filters gave the best retention efficiency with the fastest filtration times. Sample processing times were also improved by modifying the flow gradients in an existing HPLC protocol allowing the analysis of 106 samples in 24 h. The resulting protocol is suitable for incorporation into routine water quality monitoring programs, and would greatly facilitate the early detection and tracking of K. brevis blooms in coastal waters.     

Electrogenerated chemiluminescence from osmium(II) polypyridine carbonyl chloride systems

The spectroscopy, electrochemistry and electrogenerated chemiluminescence (ECL) of four osmium(II) phenanthroline carbonyl chloride complexes are reported. Three of these compounds also contain diphosphine chelating ligands. ECL is generated in acetonitrile solutions with tri-n-propylamine (TPrA) as an oxidative-reductive coreactant. ECL efficiencies (?_ecl = photons emitted per redox event) between 0.011 and 0.13 were obtained in air saturated and deoxygenated solutions with Ru(bpy)₃²⁺ (bpy = 2,2′-bipyridine) as a relative standard (?_ecl = 1). The ECL intensity peaks at a potential corresponding to oxidation of both TPrA and the osmium systems, while ECL spectra (obtained using absorption filters) are similar to photoluminescence spectra, indicating that emission is from the excited states of the osmium complexes.     

Distribution and Rate of Microbial Processes in an Ammonia-Loaded Air Filter Biofilm

The in situ activity and distribution of heterotrophic and nitrifying bacteria and their potential interactions were investigated in a full-scale, two-section, trickling filter designed for biological degradation of volatile organics and NH₃ in ventilation air from pig farms. The filter biofilm was investigated by microsensor analysis, fluorescence in situ hybridization, quantitative PCR, and batch incubation activity measurements. In situ aerobic activity showed a significant decrease through the filter, while the distribution of ammonia-oxidizing bacteria (AOB) was highly skewed toward the filter outlet. Nitrite oxidation was not detected during most of the experimental period, and the AOB activity therefore resulted in NO₂⁻, accumulation, with concentrations often exceeding 100 mM at the filter inlet. The restriction of AOB to the outlet section of the filter was explained by both competition with heterotrophic bacteria for O₂ and inhibition by the protonated form of NO₂⁻, HNO₂. Product inhibition of AOB growth could explain why this type of filter tends to emit air with a rather constant NH₃ concentration irrespective of variations in inlet concentration and airflow.Emissions of NH₃, odorous organic gasses, and dust from pig facilities cause significant problems for neighbors and the surrounding natural environment. In Denmark, swine production accounts for 34% of the total atmospheric NH₃ emission, of which 50% originates from pig house emissions (19). Furthermore, multiple volatile and very odorous organic compounds are emitted with animal house exhaust air and constitute a severe nuisance in residential areas (16, 31). While biofilters based on wood chips, compost, and peat have proven efficient in removing complex mixtures of volatile organic compounds (VOC) from piggery exhaust air, biotrickling filters have been shown to be efficient in both odor and NH₃ removal (30). In these filters, airborne VOC and NH₃ are taken up by an irrigated biofilm and oxidized by organoheterotrophic and nitrifying bacteria, respectively, resulting in the production of CO₂, NO₂⁻ or NO₃⁻, and microbial biomass (43). The nitrification process, which comprises the two-step oxidation of NH₃ via NO₂⁻ to NO₃⁻, is catalyzed by ammonia-oxidizing bacteria (AOB) and ammonia-oxidizing archaea and by nitrite-oxidizing bacteria (NOB), respectively (22, 23). However, in many biotrickling filters, NOB activity seems to be absent, resulting in NO₂⁻ being the end product of nitrification (29).Waste products often accumulate in biotrickling filters, as the water is recycled many times to minimize wastewater discharge. In particular, NO₂⁻ may accumulate to concentrations above 100 mM (29), resulting in high levels of free nitrous acid (FNA, or HNO₂), which is inhibitory to many microorganisms (2, 40, 50). As a result of an overall countercurrent air-water flow, FNA, VOC, and NH₃ concentrations are expected to decrease from the filter air inlet toward the outlet, potentially promoting a gradient of microbial processes and species distribution through the filter.Also, on a smaller scale, physical and chemical heterogeneity results in microgradients of substrates and O₂ within the biofilm that may affect the spatial distribution and rate of microbial processes. While considerable research effort has been given to the physicochemical aspects of filter optimization (11, 44), very little is known about the distribution, activity, and potential interactions of bacterial processes in the biofilm. Problems frequently arise, such as highly variable odor reduction, failed NH₃ removal, and filter clogging due to excess biofilm growth and slime excretion. Improved insight into the dynamics of the microbial activities may help control the biological processes in order to optimize and stabilize filter performance.In this study, the in situ activity and distribution of organoheterotrophic bacteria and AOB and the identity and NH₃ oxidation potential of the AOB were investigated in a two-section, full-scale biological air filter treating waste gas from a pig facility. Biofilms in different filter sections along a gradient of decreasing VOC and NH₃ load and NO₂⁻ accumulation were characterized. The goal was to attain a basic understanding of the microbial processes and thus filter function.     

Evaluation of Five Membrane Filtration Methods for Recovery of Cryptosporidium and Giardia Isolates from Water Samples

We evaluated the efficiency of five membrane filters for recovery of Cryptosporidium parvum oocysts and Giardia lamblia cysts. These filters included the Pall Life Sciences Envirochek (EC) standard filtration and Envirochek high-volume (EC-HV) membrane filters, the Millipore flatbed membrane filter, the Sartorius flatbed membrane filter (SMF), and the Filta-Max (FM) depth filter. Distilled and surface water samples were spiked with 10 oocysts and 10 cysts/liter. We also evaluated the recovery efficiency of the EC and EC-HV filters after a 5-s backwash postfiltration. The backwashing was not applied to the other filtration methods because of the design of the filters. Oocysts and cysts were visualized by using a fluorescent monoclonal antibody staining technique. For distilled water, the highest percent recovery for both the oocysts and cysts was obtained with the FM depth filter. However, when a 5-s backwash was applied, the EC-HV membrane filter (EC-HV-R) was superior to other filters for recovery of both oocysts (n = 53 ± 15.4 per 10 liters) and cysts (n = 59 ± 11.5 per 10 liters). This was followed by results of the FM depth filter (oocysts, 28.2 ± 8, P = 0.015; cysts, 49.8 ± 12.2, P = 0.4260), and SMF (oocysts, 16.2 ± 2.8, P = 0.0079; cysts, 35.2 ± 3, P = 0.0079). Similar results were obtained with surface water samples. Giardia cysts were recovered at higher rates than were Cryptosporidium oocysts with all five filters, regardless of backwashing. Although the time differences for completion of filtration process were not significantly different among the procedures, the EC-HV filtration with 5-s backwash was less labor demanding.     

Effects of Air Pollutants on the Composition of Stable Carbon Isotopes, deltaC, of Leaves and Wood, and on Leaf Injury

Air pollutants are known to cause visible leaf injury as well as impairment of photosynthetic CO₂ fixation. Here we evaluate whether the effects on photosynthesis are large enough to cause changes in the relative composition of stable carbon isotopes, δ¹³C, of plant tissue samples, and, if so, how the changes relate to visual leaf injury. For that purpose, several woody and herbaceous plant species were exposed to SO₂ + O₃ and SO₂ + O₃ + NO₂ for one month (8 hours per day, 5 days per week). At the end of the fumigations, the plants were evaluated for visual leaf lesions, and δ¹³C of leaf tissue was determined. Woody plants generally showed less visual leaf injury and smaller effects on δ¹³C of pollutant exposure than did herbaceous plants. If δ¹³C was affected by pollutants, it became, with few exceptions, less negative. The data from the fumigation experiments were consistent with δ¹³C analyses of whole wood of annual growth rings from two conifer tree species, Pseudotsuga menziesii and Pinus strobus. These trees had been exposed until 1977 to exhaust gases from a gas plant at Lacq, France. Wood of both conifer species formed in the polluted air of 1972 to 1976 had less negative δ¹³C values than had wood formed in the much cleaner air in 1982 to 1986. No similar, time-dependent differences in δ¹³C of wood were observed in trees which had been continuously growing in clean air. Our δ¹³C data from both relatively short-term artificial exposures and long-term natural exposure are consistent with greater stomatal limitation of photosynthesis in polluted air than in clean air.     

Studies on the growth of Thiobacillus ferrooxidans

Summary A method for enumeration of viable numbers of Thiobacillus ferrooxidans using membrane filters on ferrous-iron agar is presented. Factors affecting colony production were the concentration and brand of agar, pH of the medium, and type of membrane filter. The results suggest that inhibition of T. ferrooxidans by agar is a result of the acid hydrolysis of agar, the main product of which is d-galactose. Colony development was suppressed by aged medium, by acid-hydrolysed agar and by 0.1% galactose. Sartorius and Millipore membrane filters were suitable for the experiments, whereas Oxoid MF-50 membranes virtually suppressed the production of colonies. The method was employed to follow growth of T. ferrooxidans in pH 1.3 medium. The viable cell numbers were correlated with ¹⁴CO₂-fixation and ferrous iron oxidation. Generation time was 6 h 22 min with a yield of 2.2×10¹² organisms/g atom Fe²⁺ oxidized. Growth of T. neapolitanus on thiosulphate medium was not affected by agar-type or membrane filters and yield of the organism was 1.5×10¹³ organisms/g molecule Na₂S₂O₃ oxidized.     

Nitrogen removal from secondary effluent by using integrated constructed wetland system

The treatment capacity of an integrated constructed wetland system (CWS) that was designed to reduce nitrogen (N) from secondary effluent was explored. The integrated CWS consisted of vertical-flow constructed wetland, floating bed and sand filter. The vertical-flow wetland was filled with gravel, steel slag and peat from the bottom to the top. Vetiver zizanioides was selected to grow in the vertical-flow constructed wetland and Coix lacrymajobi L. was grown in the floating bed. The results showed that the integrated CWS displayed superior removal efficiency for nitrate nitrogen (NO₃⁻-N), ammonia nitrogen (NH₄⁺-N), nitrite nitrogen (NO₂⁻-N), and total nitrogen (TN). The average NO₃⁻-N, NO₂⁻-N, NH₄⁺-N and TN removal efficiencies of the integrated CWS were 98.83%, 95.60%, 98.05% and 92.41%, respectively, during the whole experimental operation. The integrated CWS may have a good potential for removing N from secondary effluent.     

Improving wastewater effluent filtration by changing flow regimes—Investigations in two cold climate pilot scale systems

Two pilot-scale experimental filter systems (FSs) filled with light-weight aggregates (LWA) or crushed limestone (CL) and operated under different flow regimes were established during the summer of 2005. The main objective of the study was to compare continuous-flow hybrid CL and LWA filters and batch-operated LWA filters in order to determine optimal loading, design parameters, management schemes and operational regimes for LWA-based FSs in cold climate conditions for the secondary treatment of domestic wastewater. With higher re-circulation rates of treated water, purification efficiency increased in terms of most water quality indicators in both types of filter systems. In the batch-operated FS the highest purification efficiencies of 96% and 51% for BOD₇ and N_tot, respectively, were achieved when the re-circulation rate of 200% was applied. In the continuous-flow FS the highest purification efficiencies of 99% and 81% for BOD₇ and N_tot, respectively, were achieved when the re-circulation rate up to 300% was applied. In order to achieve effective organic matter removal, nitrification/denitrification and TSS removal, the re-circulation rate must be from 100% to 300% of the inflowing wastewater. Both FS designs, the continuous-flow hybrid systems and the batch-operated filters, are suitable for the secondary treatment of domestic wastewater in cold climate conditions.     

Bioscrubber treatment of exhaust air from intensive pig production: Case study in northern Germany at mild climate condition

Treatment by field‐scale bioscrubber of exhaust air, including ammonia (NH₃) and the greenhouse gases methane (CH₄), nitrous oxide (N₂O), and carbon dioxide (CO₂), from 13 intensive pig production houses located in northern Germany were investigated in 2013 and 2015. NH₃ removal efficiencies varied between 35 and 100% with an overall average value of 79% under the NH₃ inlet fluctuations from 34 to 755 g d^?1 m^?3 in both 2013 and 2015. Results of the electron microscopic analyses demonstrated that the bacteria Nitrosomonas sp. and methanotrophs type I were the dominant NH₃ and CH₄ oxidizers, respectively. However, overall average removal efficiencies of CH₄ was approximately zero, which means CH₄ is hard to remove in bioscrubbers under normal operation. The pH of recirculation water in the bioscrubber varied from 6.1 to 8.1, and the bioscrubbers with low pH values (<7.0) had high NH₃ removal efficiencies (>79%). Electrical conductivity was commonly used to diagnose the bioscrubbers’ performance; in the present study, electrical conductivity presented a significant linear relationship with dissolved inorganic nitrogen, which indicates the performance stability of the 13 selected bioscrubbers.     

An experimental study of the oxygen consumption,growth, and metabolism of the COD (Gadus Morhua L.)

The rate of oxygen consumption of cod in sea water at 12 °C containing MS222 (25 mg/l) can be expressed as: Q_o2 = 0.245 W^0,82(mg/h), where W is the lived weight of the fish (g). The maximum efficiency of conversion of assimilated food into growth was 24% during the feeding experiment. Digestion efficiencies were estimated at over 98% using fillets of plaice as food. The effect of increasing the rate of food intake was to increase liver weight and condition factor. The relative proportions of protein and lipid in the body did not change over the range of feeding levels used. The conversion efficiency had a maximum value at an intermediate feeding rate.     

Enhanced removal efficiency of malodorous gases in a pilot-scale peat biofilter inoculated with Thiobacillus thioparus DW44

A newly isolated autotrophic bacterium, Thiobacillus thioparus DW44, which is capable of degrading sulfur-containing gases, was inoculated into a pilot-scale peat biofilter to treat the exhaust gas from a night soil treatment plant. Hydrogen sulfide (H₂S), methanethiol (MT), dimethyl sulfide (DMS) and dimethyl disulfide (DMDS) in the exhaust gas were efficiently removed for six months. Average removal ratios were 99.8% for H₂S, 99.0% for MT, 89.5% for DMS and 98.1% for DMDS at a space velocity of 46 h⁻¹ during the period of operation. No acclimation period was needed to reach such a high efficiency in the removal of the gases, indicating that the ability of this bacterium to remove these gases was occurred immediately after its inoculation to the peat. Ammonia (NH₃) in the exhaust gas was neutralized with SO₄²⁻, which is the final product of the oxidation of H₂S, MT, DMS and DMDS by the bacterium. No remarkable decline of pH, which often causes a deterioration in bacterial activity, was observed, mainly because of the reaction of SO₄²⁻ with NH₃. This study is the first report on the application of an isolated microorganism to a practical deodorizing system. The inoculation of T. thioparus DW44 into the pilot-scale peat biofilter could overcome such disadvantages of the conventional peat biofilter as a long acclimation period to reach a constant gas removability and the low removability of DMS, and resulted in enhanced removal efficiency of malodorous gases.     

Influence of CuSO4 spectral filters,daminozide, and exogenous gibberellic acid on growth ofDendranthema Xgrandiflorum (Ramat.) Kitamura ‘bright golden anne’

The response of chrysanthemum plants to gibberellic acid (GA₃) and daminozide, grown under 6% CuSO₄ and water (control) spectral filters, was evaluated to determine the involvement of gibberellins in regulation of plant height under CuSO₄ filters. The CuSO₄ filter increased the red (R)/farred (FR), and blue (B)/R ratio (R=600–700 nm; FR =700–800 nm; B=400–500 nm) of transmitted light. PPF under 6% CuSO₄ filter was reduced by about 34% compared to PPF under water filter which averaged about 750 μM·m^?2·s^?1. Control plants were shaded with Saran Wrap to ensure equal PPF as in the CuSO₄ chamber. GA₃ application increased plant height under both the control and CuSO₄ filter, but the height increase under the CuSO₄ filter was about 20% greater than that under the control filter. Daminozide treatment reduced plant height under the control and CuSO₄ filter, but the height reduction in control plants was slightly greater than under the CuSO₄ filter. The height reduction caused by daminozide was prevented by GA₃ application in plants grown under the control or CuSO₄ filter. The results suggest that GA₃ may be partially involved in height reduction under CuSO₄ filters.     

Extraction protocols for the quantification of phycobilins in aqueous phytoplankton extracts

Phycobiliproteins are light harvesting pigments in cryptophytes, cyanobacteria, and rhodophytes that allow these organisms to absorb light in the green and orange regions of the electromagnetic spectrum. Unlike chlorophylls and carotenoids, however, phycobilins are rarely quantified as part of routine photobiological studies because they require different extraction protocols. The objectives of this study were (1) to compare 10 existing methods to determine that with the highest extraction efficiency and (2) to determine the maximum time limit for the storage of phycobilins before degradation. Cells of the cryptophyte Rhodomonas salina and the cyanobacterium Synechococcus bacillaris were harvested either by centrifugation or filtration and then subjected to lyophilization, mechanical disruption, or freeze?Cthaw techniques. The extraction efficiency for pigments in cells collected on glass fiber filters was always <32?±?5% and thus always significantly lower than in samples harvested by centrifugation, which had extraction efficiencies of 53?±?6?C98?±?11%. Disruption of cells by freezing?Cthawing and sonication both resulted in significantly higher (ANOVA, p?<?0.01) extraction efficiencies than disruption with a tissue grinder. Storage of samples at ?80°C showed no significant pigment degradation over the course of 24 weeks.     

Accuracy,Precision, and Method Detection Limits of Quantitative PCR for Airborne Bacteria and Fungi

Real-time quantitative PCR (qPCR) for rapid and specific enumeration of microbial agents is finding increased use in aerosol science. The goal of this study was to determine qPCR accuracy, precision, and method detection limits (MDLs) within the context of indoor and ambient aerosol samples. Escherichia coli and Bacillus atrophaeus vegetative bacterial cells and Aspergillus fumigatus fungal spores loaded onto aerosol filters were considered. Efficiencies associated with recovery of DNA from aerosol filters were low, and excluding these efficiencies in quantitative analysis led to underestimating the true aerosol concentration by 10 to 24 times. Precision near detection limits ranged from a 28% to 79% coefficient of variation (COV) for the three test organisms, and the majority of this variation was due to instrument repeatability. Depending on the organism and sampling filter material, precision results suggest that qPCR is useful for determining dissimilarity between two samples only if the true differences are greater than 1.3 to 3.2 times (95% confidence level at n = 7 replicates). For MDLs, qPCR was able to produce a positive response with 99% confidence from the DNA of five B. atrophaeus cells and less than one A. fumigatus spore. Overall MDL values that included sample processing efficiencies ranged from 2,000 to 3,000 B. atrophaeus cells per filter and 10 to 25 A. fumigatus spores per filter. Applying the concepts of accuracy, precision, and MDL to qPCR aerosol measurements demonstrates that sample processing efficiencies must be accounted for in order to accurately estimate bioaerosol exposure, provides guidance on the necessary statistical rigor required to understand significant differences among separate aerosol samples, and prevents undetected (i.e., nonquantifiable) values for true aerosol concentrations that may be significant.Real-time quantitative PCR (qPCR) is an analytical method for the rapid and potentially sensitive enumeration of broad and specific microbial populations in environmental samples (17). For bioaerosol analysis, this method allows for detection and enumeration independent of culturing, thereby circumventing the significant concerns surrounding the unculturability of environmental microorganisms and loss of culturability due to aerosol sampling (1, 2, 18, 34, 46, 55). Over the last decade, the application of qPCR has advanced research in the human health, environmental, and the national security arenas by enabling the specific measurement of airborne allergenic mold, pathogenic bacteria, and human viruses (6, 7, 9, 13, 37, 45).The quantitative nature of this technique as well as the documented advantages over culturing provides the potential for integrating microbial measurements with physical and chemical aerosol processes to understand exposure and to describe the fate and sources of biological aerosols in indoor environments and the atmosphere. However, the logarithmic amplification that is the basis of qPCR results in significant standard deviations among repeated qPCRs (25, 50). This variability rarely constrains the use of qPCR in aquatic and terrestrial systems, where biological growth typically dictates concentrations above detection limits and multiple order-of-magnitude differences in microorganism concentrations between treatments. However, the volume concentrations of biological agents in air (10³ to 10⁶ per m³ of air) are dramatically more dilute than those measured in environmental waters (10¹² to 10¹⁴ per m³ of water) (4, 5, 10, 12, 20, 52), and processes that result in indoor and atmospheric bioaerosol concentrations are growth independent. These processes include aerosol infiltration and exfiltration, resuspension, and deposition and typically result in less than an order of magnitude of variability in aerosol or biological particulate matter (PM) concentrations (22, 29, 41). As qPCR becomes more commonly used in indoor and outdoor air quality research, it is necessary to know the analytical variability and method detection limits (MDLs) to determine whether the method is suitable for estimating exposure and delineating the experimental differences observed in aerosol processes.The goal of this study was to estimate the accuracy, precision, and MDLs associated with qPCR of aerosol samples. These concepts were applied to air sampling filters loaded with three test organisms, including spores of Aspergillus fumigatus and vegetative bacterial cells from the Gram-negative Escherichia coli and Gram-positive Bacillus atrophaeus. The efficiencies associated with DNA extraction and with extraction of whole cells from aerosol filters were measured to describe the statistical accuracy of common qPCR bioaerosol protocols. Overall precision (reproducibility) as well as instrument repeatability were determined, and a binary method for describing MDLs was developed and applied to fungal spores and bacterial cells. Such experimental and statistical treatment of qPCR-based aerosol measurements is expected to guide improved estimates of human exposure, incorporate limits of qPCR precision into experimental design, and provide a context for undetected (i.e., nonquantifiable) values.