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Background The production ban of polychlorinated biphenyl (PCB) technical mixtures has left the erroneous impression that PCBs exist only as legacy pollutants. Some lower-chlorinated PCBs are still being produced and contaminate both indoor and ambient air. Objectives To inform PCB risk assessment, we characterized lung uptake, distribution, metabolism and excretion of PCB11 as a signature compound for these airborne non-legacy PCBs. Methods After delivering [14C]PCB11 to the lungs of male rats, radioactivity in 34 major tissues and 5 digestive matter compartments was measured at 12, 25, 50, 100, 200 and 720 min postexposure, during which time the excreta and exhaled air were also collected. [14C]PCB11 and metabolites in liver, blood, digestive matter, urine and adipose tissues were extracted separately to establish the metabolic profile of the disposition. Results [14C]PCB11 was distributed rapidly to all tissues after 99.8% pulmonary uptake and quickly underwent extensive metabolism. The major tissue deposition of [14C]PCB11 and metabolites translocated from liver, blood and muscle to skin and adipose tissue 200 min postexposure, while over 50% of administered dose was discharged via urine and feces within 12 h. Elimination of the [14C]PCB11 and metabolites consisted of an initial fast phase (t½ = 9-33 min) and a slower clearance phase to low concentrations. Phase II metabolites dominated in liver, blood and excreta after 25 min postexposure. Conclusions This study shows that PCB11 is completely absorbed after inhalation exposure and is rapidly eliminated from most tissues. Phase II metabolites dominated with a slower elimination rate than the PCB11 or phase I metabolites and thus can best serve as urine biomarkers of exposure.

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Current limitations in the methodology for enumeration and identification of airborne bacteria compromise the precision and accuracy of bioaerosol exposure assessment. In this study, flow cytometry and fluorescent in situ hybridization (FISH) were evaluated for the assessment of exposures to airborne bacteria. Laboratorygenerated two-component bioaerosols in exposure chambers and complex native bioaerosols in swine barns were sampled with two types of liquid impingers (all-glass impinger-30 and May 3-stage impinger). Aliquots of collection media were processed and enumerated by a standard culture technique, microscopy, or flow cytometry after nucleic acid staining with 4,6-diamidino-2-phenylindole (DAPI) and identified taxonomically by FISH. DAPI-labeled impinger samples yielded comparable estimates of bioaerosol concentrations when enumerated by microscopy or flow cytometry. The standard culture method underestimated bioaerosol concentrations by 2 orders of magnitude when compared to microscopy or flow cytometry. In the FISH method, aliquots of collection media were incubated with a probe universally complementary to eubacteria, a probe specific for several Pseudomonas species, and a probe complementary to eubacteria for detection of nonspecific binding. With these probes, FISH allowed quantitative identification of Pseudomonas aeruginosa and Escherichia coli bioaerosols in the exposure chamber without measurable nonspecific binding. Impinger samples from the swine barn demonstrated the efficacy of the FISH method for the identification of eubacteria in a complex organic dust. This work demonstrates the potential of emerging molecular techniques to complement traditional methods of bioaerosol exposure assessment.

The air in livestock buildings contains bioaerosol levels that are sufficiently high to cause adverse health effects in animals and workers. These bioaerosols are complex mixtures of live and dead microorganisms and their products as well as other aeroallergens. The effectiveness of sampling methods used for quantifying the very high concentrations of microorganisms in these environments has not been well studied. To facilitate an accurate assessment of respiratory hazards from viable organisms in agricultural environments, three bioaerosol sampling methods were investigated: the Andersen microbial sampler method (AMS), the all-glass impinger method (AGI), and the Nuclepore filtration-elution method (NFE). These methods were studied in a parallel fashion in 24 swine confinement buildings. Measurements were taken in two seasons with three types of culture media in duplicate to assess total bacteria, gram-negative enteric bacteria, and total fungi. Methods were analyzed for the proportion of samples yielding data within the limits of detection, intraclass reliability, and correlation between methods. For sampling viable bacteria, the AMS had a poor data yield because of overloading and demonstrated weak correlation with the AGI. Conversely, the AGI and NFE gave sufficient numbers of valid data points (90%o), yielded high intraclass reliabilities (at 0.92), and were highly correlated with each other (r = 0.86). The AGI and the NFE were suitable methods for assessing bacteria in this environment, but the AMS was not. The AMS was the only method that consistently recovered enteric bacteria (73% data yield). For sampling fungi, the AGI and AMS both yielded sufficient data and all three methods demonstrated high intraclass reliability. The AGI and AMS correlated moderately with each other, but each correlated well with the NFE. However, the AGI measured significantly higher airborne fungal concentrations than did the AMS. Thus, the AGI was the preferred sampling method for viable fungi. Selection of an appropriate method depends on the purpose of sampling, expected bioaerosol concentrations, and environmental conditions. In this study, the AGI was best for total bacteria and fungi and the AMS was preferred for sampling enteric organisms.

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