Comparison of endotoxin exposure assessment by bioaerosol impinger and filter-sampling methods

Quantitative microbial risk assessment (QMRA) tool for modelling pathogen infection risk to wastewater treatment plant workers

Wastewater treatment plants (WWTPs) provide vital services to the public by removing contaminants from wastewater prior to environmental discharge or reuse for beneficial purposes. WWTP workers occupationally exposed to wastewater can be at risk of respiratory or gastrointestinal diseases. The study objectives were to: (1) quantify pathogens and pathogen indicators in wastewater aerosols near different WWTP processes/unit operations, (2) develop a QMRA model for multi-pathogen and multi-exposure pathway risks, and (3) create a web-based application to perform and communicate risk calculations for wastewater workers. Case studies for seven different WWTP job tasks were performed investigating infection risk across nine different enteric and respiratory pathogens. It was observed that the ingestion risk among job tasks was highest for "walking the WWTP," which involved exposure from splashing, bioaerosols, and hand-to-mouth contact from touching contaminated surfaces. There was also a notable difference in exposure risk during peak (5:00am-9:00am) and non-peak hours (9:00am- 5:00am), with risks during the peak flow hours of the early morning assumed to be 5 times greater than non-peak hours. N95 respirator usage reduced median respiratory risks by 77 %. The developed tool performs multiple QMRA calculations to estimate WWTP workers' infection risks from accidental ingestion or inhalation of wastewater from multiple pathogens and exposure scenarios, which can inform risk management strategies to protect occupational health. However, more data are needed to reduce uncertainty in model estimates, including comparative data for pathogen concentrations in wastewater during peak and non-peak hours. QMRA tools will increase accessibility of risk models for utilization in decision-making.

Genomic characterisation of bioaerosols within livestock facilities: A systematic review

Livestock facilities are widely regarded as reservoirs of infectious disease, owing to their abundance in particulate matter (PM) and microbial bioaerosols. Over the past decade, bioaerosol studies have increasingly utilised high throughput sequencing (HTS) to achieve superior throughput, taxonomic resolution, and the detection of unculturable organisms. However, the prevailing focus on amplicon sequencing has limited the identification of viruses and microbial taxa at the species-level. Herein, a literature search was conducted to identify methods capable of overcoming the aforementioned limitations. Screening 1531 international publications resulted in 29 eligible for review. Metagenomics capable of providing rich insights were identified in only three instances. Notably, long-read sequencing was not utilised for metagenomics. This review also identified that sample collection methods lack a uniform approach, highlighted by the differences in sampling equipment, flow rates and durations. Further heterogeneity was introduced by the unique sampling conditions, which makes it challenging to ground new findings within the established literature. For instance, winter was associated with increased microbial abundance and antimicrobial resistance, yet less alpha diversity. Researchers implementing metagenomics into the livestock environment should consider season, the microclimate, and livestock growth stage as influential upon their findings. Considering the increasing accessibility of long-read sequencing, future research should explore its viability within a novel uniform testing protocol for bioaerosol emissions.

Detection and assessment of the antibiotic resistance of Enterobacteriaceae recovered from bioaerosols in the Choqueyapu River area, La Paz - Bolivia

As a highly contaminated waterway flowing through a densely populated urban area, microbiological pollution associated with the Choqueyapu River and the absence of a wastewater treatment plant in La Paz city threatens public health. We collected air samples adjacent to this river using impingement. Laboratory analyses identified the presence of Enterobacteriaceae, reporting a maximum concentration of 86,11 CFU/m³ of sampled air. Positive samples were tested for antibiotic susceptibility against the antibiotics amoxicillin-clavulanic acid, ciprofloxacin, gentamicin, meropenem, sulfamethoxazole-trimethoprim and tetracycline via disk diffusion. The highest percentages of antibiotic resistance were registered for tetracycline (50% of isolates) and sulfamethoxazole-trimethoprim (38,9%), while the lowest resistance profile was reported for meropenem (5,6%). A comparison of results obtained on the pilot studies [elaborated during the wet season of 2018 by Chavez, 2019 and Salazar et al., 2020] and the present study has been done, highlighting seasonal effects over airborne Enterobacteriaceae concentration. Also, it was determined an increase of antibiotic resistance for tetracycline, gentamicin and ciprofloxacin; and a reduction for sulfamethoxazole-trimethoprim, meropenem and amoxicillin-clavulanic acid.

An Investigation of Airborne Bioaerosols and Endotoxins Present in Indoor Traditional Wet Markets before and after Operation in Taiwan: A Case Study

Customers in Taiwan prefer to purchase fresh foods and household supplies at indoor traditional wet markets (TWMs). The health risk to indoor TWM staff exposed to bioaerosols needs to be evaluated, since these workers spend long periods of time in the market for stall preparation, selling, and stall cleaning. This study investigated the bioaerosols present in two indoor TWMs. The results showed that the cleaning process at Market A after operations, involving the use of an agitated waterspout, was able to decrease the concentration of bacterial bioaerosols (BBs) by an average of 64%, while at the same time increasing the concentration of fungal bioaerosols (FBs) by about 2.4 fold. The chemical sanitization process at Market B after operations was able to bring about average decreases of 30.8% in BBs and 19.2% in FBs, but the endotoxin concentration increased. Hotspots were found to be associated with vendors of fresh, live poultry and fresh, raw meat/seafood. Pseudomonas spp. and Clostridiumperfringens, both of which can be pathogenic, were found to be the dominant species present in these markets, making up 35.18% to 48.74% and 9.64% to 11.72% of the bacteria present, respectively. Our results provide fundamental information on the distributions of bioaerosols and endotoxins within indoor TWMs both before and after operation.

The Overview of Methods of Nanoparticle Exposure Assessment

Nanotechnology is now widely used in industry as well as consumer products, such as electrical devices, cosmetics, medicine, and household appliances. In the life cycle of the nano-products, including production, use, and disposal, nanoparticles may be released to the environment. However, there is no current consensus on the best method for evaluating and characterizing nanoparticle exposure. Therefore, this chapter focuses on the nanoparticle exposure assessment methods and sampling techniques.

Sources of Airborne Endotoxins in Ambient Air and Exposure of Nearby Communities—A Review

Endotoxin is a bioaerosol component that is known to cause respiratory effects in exposed populations. To date, most research focused on occupational exposure, whilst much less is known about the impact of emissions from industrial operations on downwind endotoxin concentrations. A review of the literature was undertaken, identifying studies that reported endotoxin concentrations in both ambient environments and around sources with high endotoxin emissions. Ambient endotoxin concentrations in both rural and urban areas are generally below 10 endotoxin units (EU) m−3; however, around significant sources such as compost facilities, farms, and wastewater treatment plants, endotoxin concentrations regularly exceeded 100 EU m−3. However, this is affected by a range of factors including sampling approach, equipment, and duration. Reported downwind measurements of endotoxin demonstrate that endotoxin concentrations can remain above upwind concentrations. The evaluation of reported data is complicated due to a wide range of different parameters including sampling approaches, temperature, and site activity, demonstrating the need for a standardised methodology and improved guidance. Thorough characterisation of ambient endotoxin levels and modelling of endotoxin from pollution sources is needed to help inform future policy and support a robust health-based risk assessment process.

Coordinated Sampling of Microorganisms Over Freshwater and Saltwater Environments Using an Unmanned Surface Vehicle (USV) and a Small Unmanned Aircraft System (sUAS)

Biological aerosols (bioaerosols) are ubiquitous in terrestrial and aquatic environments and may influence cloud formation and precipitation processes. Little is known about the aerosolization and transport of bioaerosols from aquatic environments. We designed and deployed a bioaerosol-sampling system onboard an unmanned surface vehicle (USV; a remotely operated boat) to collect microbes and monitor particle sizes in the atmosphere above a salt pond in Falmouth, MA, United States and a freshwater lake in Dublin, VA, United States. The bioaerosol-sampling system included a series of 3D-printed impingers, two different optical particle counters, and a weather station. A small unmanned aircraft system (sUAS; a remotely operated airplane) was used in a coordinated effort with the USV to collect microorganisms on agar media 50 m above the surface of the water. Samples from the USV and sUAS were cultured on selective media to estimate concentrations of culturable microorganisms (bacteria and fungi). Concentrations of microbes from the sUAS ranged from 6 to 9 CFU/m³ over saltwater, and 12 to 16 CFU/m³ over freshwater (over 10-min sampling intervals) at 50 m above ground level (AGL). Concentrations from the USV ranged from 0 (LOD) to 42,411 CFU/m³ over saltwater, and 0 (LOD) to 56,809 CFU/m³ over freshwater (over 30-min sampling intervals) in air near the water surface. Particle concentrations recorded onboard the USV ranged from 0 (LOD) to 288 μg/m³ for PM1, 1 to 290 μg/m³ for PM2.5, and 1 to 290 μg/m³ for PM10. A general trend of increasing concentration with an increase in particle size was recorded by each sensor. Through laboratory testing, the collection efficiency of the 3D-printed impingers was determined to be 75% for 1 μm beads and 99% for 3 μm beads. Additional laboratory tests were conducted to determine the accuracy of the miniaturized optical particle counters used onboard the USV. Future work aims to understand the distribution of bioaerosols above aquatic environments and their potential association with cloud formation and precipitation processes.

Field Studies Measuring the Aerosolization of Endotoxin During the Land Application of Class B Biosolids

Endotoxins are a component of Gram-negative bacteria cell walls and are known to be present in biosolids. Endotoxins have been shown to be potent stimulators of the innate immune response causing airway irritation and shortness of breath. Class B biosolids are routinely applied to agricultural lands to enhance soil properties and can be used as an alternative to chemical fertilizers. This study investigated the aerosolized endotoxin dispersed during the land application of Class B biosolids on agricultural land and a concrete surface at two sites in Colorado, USA. Aerosolized endotoxin was captured using HiVol samplers fitted with glass fiber filters, polycarbonate filter cassettes (both open and closed) and BioSampler impinger air samplers. Endotoxins were also measured in the biosolids to allow for correlating bulk biosolids concentrations with aerosol emission rates. Endotoxin concentrations in biosolids, impinger solutions and filter extracts were determined using the kinetic Limulus amebocyte lysate assay. Aerosolized endotoxin concentration was detected from all sites with levels ranging from 0.5 to 642 EU/m³. The four types of sampling apparatus were compared, and the HiVol and open-faced cassette samplers produced higher time-weighted average (TWA) measurements (EU/m³) than the impinger and closed cassette samplers. Ambient wind speed was found to be the variable best describing the observed results with optimal wind speed for highest deposition estimated at 5 m s^-1. It is argued that HiVol air samplers are a particularly reliable approach and subsequent analyses relating TWA measurements to wind speed and biosolids characteristics were based on the measurements collected with those samplers.

The Use of Bioaerosol Sampling for Airborne Virus Surveillance in Swine Production Facilities: A Mini Review

Modern swine production facilities typically house dense populations of pigs and may harbor a variety of potentially zoonotic viruses that can pass from one pig generation to another and periodically infect human caretakers. Bioaerosol sampling is a common technique that has been used to conduct microbial risk assessments in swine production, and other similar settings, for a number of years. However, much of this work seems to have been focused on the detection of non-viral microbial agents (i.e., bacteria, fungi, endotoxins, etc.), and efforts to detect viral aerosols in pig farms seem sparse. Data generated by such studies would be particularly useful for assessments of virus transmission and ecology. Here, we summarize the results of a literature review conducted to identify published articles related to bioaerosol generation and detection within swine production facilities, with a focus on airborne viruses. We identified 73 scientific reports, published between 1991 and 2017, which were included in this review. Of these, 19 (26.7%) used sampling methodology for the detection of viruses. Our findings show that bioaerosol sampling methodologies in swine production settings have predominately focused on the detection of bacteria and fungi, with no apparent standardization between different approaches. Information, specifically regarding virus aerosol burden in swine production settings, appears to be limited. However, the number of viral aerosol studies has markedly increased in the past 5 years. With the advent of new sampling technologies and improved diagnostics, viral bioaerosol sampling could be a promising way to conduct non-invasive viral surveillance among swine farms.

Protocol Improvements for Low Concentration DNA-Based Bioaerosol Sampling and Analysis

INTRODUCTION

As bioaerosol research attracts increasing attention, there is a need for additional efforts that focus on method development to deal with different environmental samples. Bioaerosol environmental samples typically have very low biomass concentrations in the air, which often leaves researchers with limited options in choosing the downstream analysis steps, especially when culture-independent methods are intended.

OBJECTIVES

This study investigates the impacts of three important factors that can influence the performance of culture-independent DNA-based analysis in dealing with bioaerosol environmental samples engaged in this study. The factors are: 1) enhanced high temperature sonication during DNA extraction; 2) effect of sampling duration on DNA recoverability; and 3) an alternative method for concentrating composite samples. In this study, DNA extracted from samples was analysed using the Qubit fluorometer (for direct total DNA measurement) and quantitative polymerase chain reaction (qPCR).

RESULTS AND FINDINGS

The findings suggest that additional lysis from high temperature sonication is crucial: DNA yields from both high and low biomass samples increased up to 600% when the protocol included 30-min sonication at 65°C. Long air sampling duration on a filter media was shown to have a negative impact on DNA recoverability with up to 98% of DNA lost over a 20-h sampling period. Pooling DNA from separate samples during extraction was proven to be feasible with margins of error below 30%.

Assessment of workers' exposure to bioaerosols in a French cheese factory

Hundreds of different cheeses are produced in France, where 23.9kg of cheese were consumed per inhabitant in 2009, when it was ranked the second cheese-consuming nation. To meet this considerable demand, a large number of cheese factories exist where many workers, especially cheese washers, may be exposed to fungal bioaerosols that can lead to adverse toxinic and allergic effects. Airborne bacteria, fragments, or microbial by-products (endotoxins) are also found and contribute to total worker exposure. However, there is almost no published data concerning worker exposure or characteristics of bioaerosols emitted during these activities. Here, we measured the parameters (concentrations, species present, and size distribution) of the culturable fungal bioaerosol emitted in a French natural-rind cheese-maturing cellar. Concentrations of airborne bacteria and endotoxins were also measured. The main tasks were investigated using stationary or personal sampling over three consecutive days. Depending on the work area, high concentrations of culturable mesophilic microorganisms were measured (using closed-face cassettes): from 10(4) to 2×10(8) CFU m(-3) for fungi and from 10(3) to 10(6) CFU m(-3) for bacteria. These concentrations are 10- to 100000-fold higher than those measured at two reference points (indoor and outdoor) that are assumed not to be contaminated by the plant's activities. Endotoxin concentrations were between 10 and 300 EU m(-3) in the plant. Exposure was further assessed by identifying the predominant culturable fungi (allergenic Mucor fuscus and Penicillium sp.) and by measuring particle size distributions (cascade impactor). Airborne fungal entities (spores, mycelium strands and fragments, agglomerates, etc.) were found with aerodynamic diameters from 3 to over 20 µm. A metrological approach was used to fully characterize the culturable fungal aerosols generated during cheese maturing in this plant. The results show that workers are exposed to concentrations of airborne culturable fungi, sometimes very high, throughout the manufacturing process. In addition to fungi, culturable bacteria and endotoxins are also present in the work atmosphere. All these microbial organisms thus contribute in a complex manner to total worker exposure. Despite the lack of both occupational exposure limit values and standardized measuring methods, our results suggest that an immunological risk may occur among workers, especially for cheese brushers, cheese washers, and packagers who are the most exposed workers in the factory.

Endotoxins in indoor air and settled dust in primary schools in a subtropical climate

Endotoxins can significantly affect the air quality in school environments. However, there is currently no reliable method for the measurement of endotoxins, and there is a lack of reference values for endotoxin concentrations to aid in the interpretation of measurement results in school settings. We benchmarked the "baseline" range of endotoxin concentration in indoor air, together with endotoxin load in floor dust, and evaluated the correlation between endotoxin levels in indoor air and settled dust, as well as the effects of temperature and humidity on these levels in subtropical school settings. Bayesian hierarchical modeling indicated that the concentration in indoor air and the load in floor dust were generally (<95th percentile) <13 EU/m(3) and <24,570 EU/m(2), respectively. Exceeding these levels would indicate abnormal sources of endotoxins in the school environment and the need for further investigation. Metaregression indicated no relationship between endotoxin concentration and load, which points to the necessity for measuring endotoxin levels in both the air and settled dust. Temperature increases were associated with lower concentrations in indoor air and higher loads in floor dust. Higher levels of humidity may be associated with lower airborne endotoxin concentrations.

Comparison of sampling methods for the assessment of indoor microbial exposure

Indoor microbial exposure has been related to allergy and respiratory disorders. However, the lack of standardized sampling methodology is problematic when investigating dose-response relationships between exposure and health effects. In this study, different sampling methods were compared regarding their assessment of microbial exposures, including culturable fungi and bacteria, endotoxin, as well as the total inflammatory potential (TIP) of dust samples from Danish homes. The Gesamtstaubprobenahme (GSP) filter sampler and BioSampler were used for sampling of airborne dust, whereas the dust fall collector (DFC), the electrostatic dust fall collector (EDC), and vacuum cleaner were used for sampling of settled dust. The GSP assessed significantly higher microbial levels than the BioSampler, yet measurements from both samplers correlated significantly. Considerably higher levels of fungi, endotoxin, and TIP were found in the EDC compared with the DFC, and regarding fungi, the EDC correlated more strongly and significantly with vacuumed dust than the DFC. Fungi in EDC and vacuum dust correlated most strongly with airborne dust, and in particular, the measurements from the EDC associated well with those from GSP. Settled dust from the EDC was most representative of airborne dust and may thus be considered as a surrogate for the assessment of indoor airborne microbial exposure.

PRACTICAL IMPLICATIONS

Significant discrepancies between sampling methods regarding indoor microbial exposures have been revealed. This study thus facilitates comparison between methods and may therefore be used as a frame of reference when studying the literature or when conducting further studies on indoor microbial exposure. Results also imply that the relatively simple EDC method for the collection of settled dust may be used as an alternative to otherwise tedious and time-consuming airborne dust sampling.

Measurement of endotoxins in bioaerosols at workplace: a critical review of literature and a standardization issue

Endotoxins are lipopolysaccharides found in the outer membrane of most Gram-negative bacteria and cyanobacteria. Worker exposure to endotoxins has been shown in a number of work situations and is associated with both respiratory and systemic pathologies. The lack of an occupational exposure limit is mainly due to the absence of a standard protocol at the international level for sampling and analyzing airborne endotoxins. The bibliographic review in this article takes an exhaustive look at the current knowledge on measuring airborne endotoxins. It shows that, despite several reference documents at the international level, the methods used to measure endotoxin exposure differ considerably from one laboratory to another. Standardization is necessary to reduce interlaboratory variability and, ultimately, to improve the use of interstudy data. The bibliographic review presents the current status of standardization for airborne endotoxin measurement methods in the workplace and summarizes areas for further research. This article is both a reference document for all operators wishing to use such methods and a working document to build international consensus around the measurement of airborne endotoxins.

Airborne endotoxin from indoor and outdoor environments: effect of sample dilution on the kinetic Limulus amebocyte lysate (LAL) assay

Airborne endotoxins in occupational environments are a potential respiratory hazard to individuals. In this study, airborne endotoxins were collected using open-face and button aerosol samplers from inside animal housing units and downwind from agricultural production sites and a wastewater treatment plant. Filter extracts were then diluted to examine the effect of interfering substances on the kinetic Limulus amebocyte lysate (LAL) assay. In most cases, the overall endotoxin concentration was shown to decrease with increasing dilution up to 1000-fold, suggesting the presence of enhancing substances in the filter extracts. This dilution-dependent effect was most prominent in the open-face endotoxin samples, while button samples displayed little effect. Using a joinpoint regression model, it was determined that a dilution factor of 50 to 100 was generally sufficient to eliminate the presence of enhancing substances. After screening the data for dilution dependent effects, the airborne endotoxin concentrations were determined. The highest endotoxin concentrations, ranging from 2841 to 49,066 endotoxin units m(-3) of air, were found inside swine farrowing and finishing barns. Airborne endotoxin concentrations were 10- to 100-fold lower inside a dairy barn and downwind of other agricultural production sites and the wastewater treatment plant. Examination of dilution-dependent effects should be considered essential when utilizing the LAL assay, especially if values are to be used for regulatory purposes.

Impact of production systems on swine confinement buildings bioaerosols

Hog production has been substantially intensified in Eastern Canada. Hogs are now fattened in swine confinement buildings with controlled ventilation systems and high animal densities. Newly designed buildings are equipped with conventional manure handling and management systems, shallow or deep litter systems, or source separation systems to manage the large volumes of waste. However, the impacts of those alternative production systems on bioaerosol concentrations within the barns have never been evaluated. Bioaerosols were characterized in 18 modern swine confinement buildings, and the differences in bioaerosol composition in the three different production systems were evaluated. Total dust, endotoxins, culturable actinomycetes, fungi, and bacteria were collected with various apparatuses. The total DNA of the air samples was extracted, and quantitative polymerase chain reaction (PCR) was used to assess the total number of bacterial genomes, as a total (culturable and nonculturable) bacterial assessment. The measured total dust and endotoxin concentrations were not statistically different in the three studied production systems. In buildings with sawdust beds, actinomycetes and molds were found in higher concentrations than in the conventional barns. Aspergillus, Cladosporium, Penicillium, and Scopulariopsis species were identified in all the studied swine confinement buildings. A. flavus, A. terreus, and A. versicolor were abundantly present in the facilities with sawdust beds. Thermotolerant A. fumigatus and Mucor were usually found in all the buildings. The culturable bacteria concentrations were higher in the barns with litters than in the conventional buildings, while real-time PCR revealed nonstatistically different concentrations of total bacteria in all the studied swine confinement buildings. In terms of workers' respiratory health, barns equipped with a solid/liquid separation system may offer better air quality than conventional buildings or barns with sawdust beds. The impact of ventilation rates, air distribution, or building design still has to be explored.

Concentrations of bioaerosols, odors, and hydrogen sulfide inside and downwind from two types of swine livestock operations

Few data on in-barn and downwind concentrations of endotoxin, bioaerosols, and odors from livestock facilities are available, and no studies have compared conventional confinement operations with the more animal-friendly hoop operations. Hoops are open to the environment and use a composted bedding system rather than housing pigs on slatted floors over pits holding manure slurry as in conventional confinements. We assessed airborne toxicants upwind, in barns, and downwind and evaluated determinants of exposure. Inhalable particulate matter, endotoxin, odor threshold, hydrogen sulfide, culturable mesophilic bacteria, culturable fungi, and total airborne microbes, along with wind speed, temperature, and humidity were measured at separate midsized livestock facilities (one hoop, one confinement) in Central Iowa on 10 occasions over 2 years. Significant differences in contaminants were observed between hoops and confinement buildings and across seasons for endotoxin, odors, airborne microorganisms, and hydrogen sulfide. For hoops and confinements, respectively, geometric mean in-barn concentrations were 3250 and 3100 EU/m(3) for endotoxin; 1400 and 1910 microg/m(3) for particulates; 19.6 and 146 ppb for hydrogen sulfide; 137 and 428 dilutions for odor threshold; and 3.0 x 10(6) and 1.5 x 10(6) organisms/m(3) for total microbes. Endotoxin, odor, and culturable microorganisms exceeded recommended exposure limits. Reduced analysis of variance models for these contaminants demonstrated differences by barn type, season, number of pigs, and, in some cases, temperature and humidity. Both types of swine operations produced high airborne concentrations of endotoxin, odor, hydrogen sulfide, bacteria, and fungi. Endotoxin and odors were found downwind at concentrations previously associated with adverse health effects.

Sustainability of land application of class B biosolids

Land application of Class B biosolids is routinely undertaken in the United States. However, due to public concern over potential hazards, the long-term sustainability of land application has been questioned. Thus, the objective of this review article was to evaluate the sustainability of land application of Class B biosolids. To do this we evaluated (i) the fate and transport of potential biological and chemical hazards within biosolids, and (ii) the influence of long-term land application on the microbial and chemical properties of the soil. Direct risks to human health posed by pathogens in biosolids have been shown to be low. Risks from indirect exposure such as aerosolized pathogens or microbially contaminated ground water are also low. A long-term land application study showed enhanced microbial activity and no adverse toxicity effects on the soil microbial community. Long-term land application also increased soil macronutrients including C, N, and, in particular, P. In fact, care should be taken to avoid contamination of surface waters with high phosphate soils. Available soil metal concentrations remained low over the 20-yr land application period due to the low metal content of the biosolids and a high soil pH. Soil salinity increases were not detected due to the low salt content of biosolids and irrigation rates in excess of consumptive use rates for cotton. Our conclusion, based on these studies, is that long-term land application of Class B biosolids is sustainable.

Optimization of airborne endotoxin exposure assessment: effects of filter type, transport conditions, extraction solutions, and storage of samples and extracts

Endotoxin exposure occurs in homes and occupational environments and is known to cause adverse health effects. In order to compare results from different studies and establish standards, airborne endotoxin exposures should be assessed using standardized methods. Although the European Committee for Standardization (CEN) developed guidelines for endotoxin exposure assessment, these leave room for individual interpretation. The influence of methods of sampling, extraction, and analysis has never been investigated in a full experimental design. Thus, we sought to fully elucidate the importance of all facets of endotoxin assessment. Inhalable dust samples collected simultaneously were used to investigate the effects on and interactions with airborne endotoxin concentration in two working environments of filter type (glass fiber or Teflon), transport conditions (with/without desiccant), sample storage (-20 or 4 degrees C), extraction solution (pyrogen-free water [PFW] or PFW plus 0.05% Tween 20), extract storage (-20 or 4 degrees C), and assay solution (PFW or PFW plus 0.05% Tween 20). Four hundred samples were collected and randomly distributed over the 20 combinations of treatments. There were no differences found for transport conditions and storage temperature of extracts. Also, no interactions between study variables existed. Sampling on glass-fiber filters, storage of samples in the freezer, and extraction in PFW plus 0.05% Tween 20 resulted in 1.3-, 1.1-, and 2.1-fold-higher estimated endotoxin concentrations, respectively. Use of PFW plus 0.05% Tween 20 in the assay solution had an additive effect. Thus, this study investigated gaps in the CEN protocol and provides data with which to fully specify a protocol for standardization of endotoxin exposure assessment.

Alveolar macrophage cytotoxic activity is inhibited by 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), a carcinogenic component of cigarette smoke

4-(Methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) is a carcinogenic compound of cigarette smoke that generates electrophilic intermediates capable of damaging DNA. Recently, we have shown that NNK can modulate mediator production by alveolar macrophages (AM) and bronchial and alveolar epithelial cells, suggesting that cigarette smoke can alter lung immune response. Thus, we investigated the effect of NNK and cigarette smoke extract (CSE) on AM capacity to eliminate tumoral cells. Rat AM cell line, NR8383, was treated with NNK (500 microM) or CSE (3%) and stimulated with lipopolysaccharide (10 ng/ml). The release of cytotoxic mediators, tumor necrosis factor (TNF) and reactive oxygen species (ROS), was measured in cell-free supernatants using ELISA and superoxide anion production. TNF- and ROS-dependent cytotoxicity were studied using a (51)Chromium-release assay and WEHI-164 and P-815 cell lines. Treatment of AM with NNK and CSE for 18 h significantly inhibited AM TNF release. CSE exposure resulted in a significant increase of ROS production, whereas NNK did not. TNF-dependent cytotoxic activity of NR8383 and freshly isolated rat AM was significantly inhibited after treatment with NNK and CSE. Interestingly, although ROS production was stimulated by CSE and not affected by NNK, CSE inhibited AM ROS-dependent cytotoxicity. These results suggest that NNK may be one of the cigarette smoke components responsible for the reduction of pulmonary cytotoxicity. Thus, NNK may have a double pro-carcinogenic effect by contributing to DNA adduct formation and inhibiting AM cytotoxicity against tumoral cells.

Application of flow cytometry for the assessment of preservation and recovery efficiency of bioaerosol samplers spiked with Pantoea agglomerans

Exposure assessment of biological aerosols requires trade-offs between efficient sampling of airborne microorganisms as either particles or viable units. The main objective of this work was to characterize aspects of bioaerosol measurement efficiency. A known concentration of the vegetative bacteria Pantoea agglomerans was spiked onto different samplers (AGI-30, BioSampler, and membrane filters) and then run for increasing time periods using HEPA filtered air. Measurement efficiency was evaluated based on total, viable, and culturable counts. Total and viable counts were determined by flow-cytometry (FCM); culturable counts were evaluated by standard plating. FCM as a method for assaying viability showed excellent agreement with known proportions of live/dead organisms (slope = 0.82, R(2) = 0.99). P. agglomerans recoveries (total, viable, and culturable) in order of best sampler performance included the BioSampler (75%, 52%, and 50%), filtration (50%, 13%, and 2%), and the AGI-30 (<30%, 15%, and 5%). The difference between viability and culturability provided an indication of viable but nonculturable (VBNC) cells. VBNC efficiency for sampling by filter, AGI-30, and BioSampler was 80%, 50%, and 100%, respectively. This research helps characterize recovery, survival, and culturability efficiencies while sampling environmentally sensitive airborne bacteria for purposes of exposure assessment, epidemiologic studies, and homeland security.

Detection of airborne Legionella while showering using liquid impingement and fluorescent in situ hybridization (FISH)

Aerosols of water contaminated with Legionella bacteria constitute the only mode of exposure for humans. However, the prevention strategy against this pathogenic bacteria risk is managed through the survey of water contamination. No relationship linked the Legionella bacteria water concentration and their airborne abundance. Therefore, new approaches in the field of the metrological aspects of Legionella bioaerosols are required. This study was aimed at testing the main principles for bioaerosol collection (solid impaction, liquid impingement and filtration) and the in situ hybridization (FISH) method, both in laboratory and field assays, with the intention of applying such methodologies for airborne Legionella bacteria detection while showering. An aerosolization chamber was developed to generate controlled and reproducible L. pneumophila aerosols. This tool allowed the identification of the liquid impingement method as the most appropriate one for collecting airborne Legionella bacteria. The culturable fraction of airborne L. pneumophila recovered with the liquid impingement principle was 4 and 700 times higher compared to the impaction and filtration techniques, respectively. Moreover, the concentrations of airborne L. pneumophila in the impinger fluid were on average 7.0 x 10(5) FISH-cells m(-3) air with the fluorescent in situ hybridization (FISH) method versus 9.0 x 10(4) CFU m(-3) air with the culture method. These results, recorded under well-controlled conditions, were confirmed during the field experiments performed on aerosols generated by hot water showers in health institutions. This new approach may provide a more accurate characterization of aerobiocontamination by Legionella bacteria.

Particle size distributions and concentrations of airborne endotoxin using novel collection methods in homes during the winter and summer seasons

A comparison study of novel collection methods for airborne bacteria and endotoxin was performed in an environmentally controlled chamber and in pilot-field studies. Airborne particulate matter was collected in swirling liquid impingers, air-monitoring filter cassettes, and with a micro-orifice uniform deposit impactor (MOUDI) to evaluate aerodynamic particle size distributions. Environmentally controlled chamber studies showed that impingers and MOUDI recovered significantly more airborne bacteria than filter cassettes, whereas collection methods for airborne endotoxin were not significantly different. In addition, total airborne bacteria and endotoxin concentrations were measured indoors and outdoors at three homes in Boulder, CO during winter and summer seasons. Indoor concentrations collected with the three different samplers were significantly different for airborne endotoxin, but not for airborne bacteria. Total airborne bacteria indoors and outdoors significantly varied with seasons. Outdoor airborne endotoxin significantly varied with season; no seasonal variation was seen for indoor airborne endotoxin. Indoor and outdoor levels were not significantly different for both airborne bacteria and endotoxin. The largest proportion of endotoxin was associated with airborne particulate matter <1 microm.

PRACTICAL IMPLICATIONS

This study compared sampling methods for airborne endotoxin, a potent and nonspecific immune system stimulant which can induce negative health responses. The data from this study showed that swirling liquid impingers and the micro-orifice uniform deposit impactor (MOUDI) recovered significantly more airborne endotoxin than the more widely adapted method of collecting airborne endotoxin on membrane filters, when collection methods were applied in realistic settings (homes). The MOUDI measured the particle size distribution of airborne endotoxin, which can be useful for determining endotoxin respiratory toxicity and its health effects.

The measurement of aerosolized endotoxin from land application of Class B biosolids in Southeast Arizona

The purpose of this study was to determine aerosolized endotoxin concentrations downwind of a biosolids land application site. Aerosol samples were collected from biosolids land application sites, tractor operation, and an aeration basin located within an open-air wastewater treatment plant. Aerosolized endotoxin above background concentrations was detected from all sites, at levels ranging from below detection up to 1800 EU m–3 of air. Biosolids loading operations resulted in the greatest concentrations of endotoxin (mean 344 EU m–3). As downwind (perpendicular to wind vector) distance increased from sources (2–200 m), levels of endotoxin decreased to near background (without biosolids application) concentrations. Overall, the detected levels of aerosolized endotoxin were within past proposed aerosolized endotoxin limits (250–2000 EU m–3) by other occupational exposure studies. Occasionally, peak concentrations were found to be above these limits. Sites in which soil was being aerosolized resulted in greater concentrations of endotoxin with or without biosolids, which suggested that the majority of endotoxin may in fact be of soil origin. This study evaluated the presence of aerosolized endotoxin from the land application of biosolids and showed that these levels were within ranges for concern suggested by other studies and that this area of research needs further investigation. Key words: biosolids, endotoxin, aerosol, bioaerosol, lipopolysaccharide.

Bioaerosols from municipal and animal wastes: background and contemporary issues

Global population increases, coupled with intensive animal and livestock production practices, have resulted in the generation, accumulation, and disposal of large amounts of wastes around the world. Aerosolization of microbial pathogens, endotoxins, odors, and dust particles is an inevitable consequence of the generation and handling of waste material. Bioaerosols can be a source of microbial pathogens, endotoxins, and other allergens. Given the close proximity of population centers to concentrated animal-rearing operations and municipal treatment facilities in many parts of the world, there is concern regarding the occupational and public health impacts associated with the exposure to bioaerosols from municipal and animal wastes. Major advances have been made in our understanding of bioaerosol characteristics, identifying the hazards, and identifying possible human and animal health links with aerosolized pathogens and allergens. However, significant knowledge and technology gaps still exist. These include a lack of clear understanding of the fate and transport of bioaerosols, especially within the open environment, an inability to accurately predict the health risks associated with bioaerosolized pathogens, and a lack of standardized bioaerosol sampling protocols, and efficient samplers. This review synthesizes the information related to bioaerosols and addresses the contemporary issues associated with bioaerosols from municipal and animal wastes, with a focus on pathogens.