Contaminated tomatoes have become a commonly implicated vehicle of Salmonella outbreaks. Exposure of tomatoes to pathogen could occur in the field. Blossom inoculation with Salmonella can result in contaminated fruit but natural routes of blossom contamination are not well known. Salmonellae have been known to survive in agricultural soil. Since dispersal of soil particulate by wind is a common phenomenon, the potential of airborne soil particulate as a vehicle of Salmonella contamination in tomato blossoms was examined. It was determined that Salmonella enterica serotype Anatum, Baildon, Braenderup, Montevideo, Newport, Javiana had similar survival patterns in both soil and water. At the end of 40 days, populations of Salmonella in soil dropped by 2.59 log CFU/g and 5.11 log CFU/g when enumerated on Tryptic Soy Agar Yeast Extract (TSAYE) and xylose lysine Tergitol 4 (XLT4) agar respectively. Salmonella populations in water reduced by 2.55 log CFU/ml (TSAYE, enumeration) and 2.94 log CFU/ml (XLT4, enumeration). Blossom to fruit formation takes 20-30 days in tomatoes hence the introduction or presence of the pathogen in agricultural soil and water could increase risk of blossom contamination. Also, it was determined that all Salmonella serotypes tested were capable of biofilm production on glass coverslips and quartz particles. Biofilm based attachment of Salmonella to sand might aid in its dispersal. To visualize transfer of pathogen from soil particulate to blossom in real-time, bioluminescent S. Baildon, S. Braenderup, S. Newport, S. Javiana and S. Anatum were created.Heat shock procedure was developed to improve electrotransformation efficiency in Salmonella. Transformed strains were compared for bioluminescence production and plasmid stability. S. Newport had the best bioluminescence properties but no difference was observed between strains for plasmid stability. Imaging of soil particulate - S. Newport mixture inoculated blossoms, indicated that the event led to pathogen transfer to blossom. It was also determined that S. Newport â soil particulate contaminated blossoms developed into fruits that were positive for S. Newport. S. Newport presence in blossom, fruit surface and internal tissue indicates that contaminated soil particulate could serve as a vehicle of tomato contamination. / Ph. D.

When a large area of open gob collapses suddenly, a windblast is produced that can cause considerable damage throughout the infrastructure of a mine. In a few cases, the windblast has been accompanied by ignitions of methane and/or coal dust. Analytical and numerical analyses investigated the transient behavior of the air through the small time period during which the roof is falling. This is sufficiently short to allow adiabatic compression of the air, i.e. negligible heat transfer to rock surfaces. Controlled escape of the air via interconnecting entries limits the build-up of air pressure. However, this same phenomenum causes the potential energy of the falling strata to be concentrated into a diminishing mass of air. Computer simulations predicted that the temperature of the air would increase rapidly as the roof descends, reaching values that are capable of igniting either methane or coal dust. This thesis concentrates on a series of laboratory tests involving the compression of mixtures of air, methane and coal dust under a falling weight and while allowing controlled escape of the mixture. The transient responses on pressure and temperature sensors were recorded. In addition to an analysis of those records, the thesis highlights those conditions in which ignitions occurred. / Master of Science

The frequency of dust storms is increasing globally yet it is often difficult to determine dust sources in mixed events. Dust events may negatively impact human health, but the composition of major dust sources is not well characterized in arid regions globally. In the western US, the National Wind Erosion Research Network (NWERN) has various sites evaluating seasonal dust emissions to quantify dust fluxes. We used existing dust samples to characterize the isotopic, chemical, and mineralogical composition of dust over multiple seasons from ten representative NWERN sites and compared with land use, vegetation, and surficial geology. Our results show variability in dust chemistry across the ten sites primarily related to differences in surficial geology (local bedrock and sediment) with other factors playing a minor role. In some cases, seasonal vegetation and wind direction played a role in controlling dust composition. For example, the El Reno site showed seasonal differences in mineralogy related to carbonate precipitation and dissolution in the soil during wet summers and dry winters. The Holloman Air Force Base (HAFB) site had distinct seasonal changes in dust chemistry with spikes in Na, Mg, Ca, Ni, and Sr during the spring months possibly related to changes in wind direction and inputs from neighboring White Sands National Park. The Lordsburg Playa site had distinct chemistry relative to other sites with high concentrations of Li, Na, Ca, and Sr due to the prevalence of evaporite minerals. Mineralogy results show the presence of quartz, phyllosilicates, and feldspar minerals at each of the NWERN sites with HAFB also containing calcium sulfate and iron oxide minerals. The 87Sr/86Sr results showed lower ratios correlating with younger bedrock (e.g., ~0.7075 at the Red Hills site surrounded by Miocene volcanic rocks), but some of the sites with recent surficial sediments had higher ratios (e.g., ~0.714 at the CPER site with Tertiary sediments). By creating a library of isotopic, chemical, and mineralogical data for dust sources across the western US, our dataset has implications for identifying characteristics that may be used for tracking dust sources.

Interstellar dust plays an important role in the physics of the interstellar medium, as well as the formation and evolution of stars. The presence of dust is often indicated in optical images by dark lanes which bisect spiral galaxies, or seen directly as reflection nebulosity around stars or emission nebulosity if sufficient heating is present. Of interest in this thesis is the dust that is associated with bipolar outflow sources. Bipolar outflows can occur in either evolved stars or in young stellar objects, and are so named because they consist of two lobes which are thought to be due to out-flowing dust and gas, with a dark lane between them due to thick dust in a circumstellar disk or shell which often blocks the light from the central star. The spatial distribution of the properties of dust around bipolar outflow sources has been examined using a combination of theoretical and observational techniques. To aid the interpretation of observations of bipolar outflow sources, we have modelled the wavelength dependence of light from 0.36 to 22\um, scattered by dust particles with varying characteristics. The results were then presented in the form of colour excess ratios. These model ratios can be applied to observations if the contribution due to the central star is able to be removed, such that all that remains in the image is the effect of the dust particles. The scattering of light by dust particles was modelled by varying six different characteristics: grain material, size (particle radius from 0.002 to 0.75\um), mantle temperatures and thicknesses, shape, and orientation. Of those characteristics, the largest variation in the colour excess ratios resulted from varying grain composition and size. Different scattering angles also produce a noticeable variation in the colour excess ratios, however the effect is difficult to distinguish from the general extinction due to dust around the source. Water ice mantles were also found to significantly change the colour excess ratios. Grain shape and orientation produced only small variations in the colour excess ratios. Three bipolar outflow sources were studied as part of this thesis, two evolved objects, OH~231.8+4.2 and Mz\,3, and the young T-Tauri object Rno\,91. The observations involved multi-wavelength imaging in the infrared, from which colours and colour excess ratios were obtained at various points of the bipolar outflows and then compared to the predictions made in the modelling. The most extensive data set analysed was seven images of the object OH~231.8+4.2 which were used in a multi-wavelength study in the infrared H to N bands (1.25--12\um). The central source position of the object has been confined to less than an arcsec using the longer wavelength images and an L--M colour image. The two peaks which dominate the lobes in the shorter wavelength images were found to be scattering peaks where the light from the central source is scattered from the walls of the lobes. The spatial distribution of water ice in the nebula has also been constrained to the circumstellar disk which has a torus or disk shape rather than being a spherical shell. The colour excess ratios derived for the nebula from the images also suggest slightly different dust properties between the circumstellar disk, lobe walls and within the lobe cavities. The young T-Tauri star Rno\,91 also contains ice, and was observed between J and L. The central star which illuminates the nebula was shown to be coincident with the brightest point in these images. Using colour excess ratio results for various parts of the nebula, it was shown that the dust close to the central star is likely to contain larger grains than the diffuse ISM, but with a similar composition. Moving away from the central star, the dust becomes more like that observed in the diffuse ISM. The presence of water ice on dust close to the central star was confirmed using images centred in the ice band. The protoplanetary bipolar outflow source Mz\,3 is slightly more evolved than OH 231.8+4.2, and does not have evidence of any water ice in the circumstellar disk. Images of this object were obtained between J and 10\um. The presence of warm dust throughout the inner bipolar lobes of this object is noticeable by the brightness of the lobes in the image at 10\um. Line profiles through the position of the central source of the 10\um\ image demonstrate that there is a circumstellar shell close to the central source which has an inner radius of $\lta\,375$\,AU. Colour excess ratio results for the bipolar lobes suggest that the dust associated with Mz\,3 is generally smaller than that found in the diffuse ISM. The properties of the dust in the bipolar lobes were also observed to be different to the dust closer to the central source and lying in the circumstellar disk. The small sizes for dust in Mz\,3 is consistent with the high velocity outflows that have been associated with the object.

Dust particles in the atmosphere are a key cause of nuisance, health and other environmental problems. The mining sector is a major source of airborne particulate matter caused by operations like terrain clearing, drilling, blasting, tipping and loading and the passage of vehicles on unpaved roads. The nuisance effect of airborne dust can be measured by using dust buckets and/or directional dust deposition gauges. Dust buckets are used to determine vertical dust deposition rates and directional dust deposition gauges are used to determine the direction of the sources. Traditionally the measurement of the vertical flux of dust, or dust deposition has been used as to indicate the nuisance caused by coarse suspended particulate matter. Several countries have produced standards for permissible dust deposition rates. Although alternative deposition measurement methods have been proposed, ASTM D1739 has remained the method most often used in the South African mining and industrial sectors to measure dust deposition. In addition, a number of non-standard directional dust deposition gauges have been used. SANS 1929:2005 (South African National Standards, 2005) prescribes the use of ASTM D1739:98 for measuring dust deposition. However, for historical reasons the previous version, ASTM D1739:70 (re-approved as ASTM D1739:82) is still widely used and in the recently promulgated South African Dust Management regulations the use of this version is prescribed. In order to determine the difference in the results obtained by the two versions, ASTM D1739:82 and ASTM D1739:98 were used to measure dust deposition levels arising from a coal mining operation in the Mpumalanga Province and a gold mining operation in North-West Province. In order to determine whether a correlation exists between vertical dust flux (dust deposition) and horizontal dust flux, standard directional horizontal dust flux gauges according to BS 1747 part 5 were also set up at both sites. The measurement of dust deposition using three dust deposition gauges (i.e. ASTM D1739:82, ASTM D1739:98 and BS 1747 part 5, directional dust deposition gauges) was undertaken monthly over a period of fourteen (14) months at the two sites. The findings of the study indicate that the dust deposition rates for an opencast coal mine are generally higher than the dust deposition rates for an underground gold mine. ASTM D1739:98 was shown to be a more efficient dust deposition collection method than ASTM D1739:82, with the ratio between the mean values slightly more than 2. The addition of water to the dust bucket does not make a statistically significant difference to retention of dust in the bucket. There is a weak correlation between results for the vertical dust gauges and horizontal dust flux. It is recommended that the South African mining sector continue dust deposition monitoring and reporting using the more recent version of ASTM D1739, as high deposition levels may indicate a potential health impact from PM10 thoracic dust. / Dissertation (MEng)--University of Pretoria, 2014. / gm2014 / Chemical Engineering / unrestricted

Mineral dust has manifold impacts on the Earth system. This includes land degradation at the dust sources, interaction with radiation in the atmosphere and effects on human health and economic activity. While it can be stated that most dust sources are found in arid and semi-arid environments, a general determination of characteristics that make a surface particularly susceptible to wind erosion cannot be given. One dust source type that has gained increasing attention in recent years is alluvial sediments. These sediments are formed and influenced by surface runoff and provide a large amount of fine grained material prone to wind erosion. Alluvial features are abundant in desert regions but are often small in size, for example dry river basins or alluvial fans. Due to their small size and despite their importance, these features are often underestimated or completely disregarded in dust-emission models. In this thesis, the spatio-temporal distribution of active alluvial dust sources is investigated and parameterized for a dust-emission model. For this, an approach to automatically detect alluvial features from two globally available satellite products is developed. These products comprise (1) surface reflectance at visible and near-infrared wavelengths derived from Sentinel-2 or MODIS and (2) HydroSHEDS flow accumulation data based on radar measurements. By combining these two datasets, an alluvial fines map (AFM) is created that shows the distribution of alluvial sediments. The AFM is implemented in a dust-emission model and multi-year model runs are performed for two study regions, one located around the Aïr Massif in the central Sahara, the other one covering western Namibia. Besides the distribution of fine alluvial sediments, another hydrologically influenced source type is analyzed in Namibia, i.e. the Etosha pan, a salt pan that is one of the most important dust sources in southern Africa. Dust activity from Etosha pan exhibits a strong seasonality due to regular flooding of the pan. These inundation events are implemented in the model by creating a monthly water mask from MODIS reflectance data. In the central Saharan study area, a comparison of the simulated dust flux with observed dust source activation frequency (DSAF) derived from the MSG SEVIRI Desert-Dust-RGB product shows that the model is able to reproduce the spatial and seasonal differences in the main activity of the identified sources. This seasonality cannot be reproduced by a control model run, in which the sediment supply by alluvial features is not included explicitly. For the Namibian study area, a model run is performed that includes the monthly water mask for Etosha pan and the AFM for the coastal ephemeral river basins. The simulated period covers 13 years from 2005 to 2017. With an empirical orthogonal function (EOF) analysis, constellations of pressure systems in the southern African region are determined that lead to an increased dust flux from the study area. Especially the Berg wind situation, a unique pressure pattern found in southern Africa with dry and hot continental winds, is identified as an atmospheric circulation pattern that leads to increased dust activity from the Namibian sources. The results highlight how important the consideration of alluvial features is for an accurate simulation of dust fluxes. Due to the global availability of the satellite data, the approach can be implemented in regional, continental or even global studies. Long-term emission fluxes can be used to identify the influence of meteorological patterns on dust emission and can help to estimate dust fluxes under current conditions but also in a changing climate.

<p></p><p>In the grain handling and processing industry, dust emission and accumulation are major concerns for the safety of workers and for explosion risks. Dust emission and accumulation locations highly depend on the facility design and equipment used for handling and processing. To prevent an explosive atmosphere, monitoring the amount of dust accumulated or dispersed is extremely important. However, methods of measuring the dust concentration require the installation of equipment. The Occupational Safety and Health Administration (OSHA) regulations and National Fire Protection Association (NFPA) standards restrict the thickness of dust layers on floors for fine powder materials such as starch. The objective of this dissertation was to better understand the rate of dust layer accumulation, dust suspension patterns, and the optical properties of suspended dust. For this purpose, The Discrete Phase Model (DPM) was combined with a Computational Fluid Dynamics Model (CFD) and the hybrid model was used to model dust dispersion. Dust dispersion patterns under pressure, such as primary explosions or leakage from equipment, were simulated using the unsteady CFD-DPM approach. The particle-wall interaction based on energy conservation was also introduced in this model. Both one-time and continuous dust dispersion in an enclosed chamber were simulated to mimic secondary explosions and the dust emission from processing equipment. In addition, the light extinction property of suspended dust was studied as a method of measuring suspended dust concentration. </p> <p>For a one-time dust dispersion incident, the predicted dust concentration agreed with the simulation result for the trial conducted at a dust injection velocity of 2 m/s with injection rates of 0.05 and 0.10 kg/m³ and at a dust injection velocity of 10 m/s with an injection rate of 0.05 kg/m³. The dust concentration in the entire chamber increased with dust injection velocity and the mass of injected dust. As dust injection velocity increased, dust spread out and formed a larger explosive dust cloud. However, the dust concentration inside the chamber was non-uniform. Considering the minimum explosive concentration, the largest explosive cloud was created at a dust injection velocity of 10 m/s with an injection rate of 0.10 kg/m³. Explosive concentrations of dust were found somewhere in the chamber for all dispersion rates. At an injection velocity of 10 m/s with an injection rate of 0.10 kg/m³, the predicted dust concentration was 10% more than the measured dust concentration. Thus, this model is suitable for dilute dust particle dispersion flows, where the volume fraction of particles is less and only a single particle layer settles.</p> <p>Continuous dispersion was simulated to determine the suspended dust concentration and particle deposition patterns. Dust was dispersed for 30 s at dispersion rates of 2, 4 and 6 g/min at a dust injection velocity of 2 m/s. The dust concentration increased at a constant rate after a few seconds of dispersion, regardless of the dust dispersion rate. Most dust particles were deposited near the dust dispersion nozzle. Large particles were more affected by gravitational force and inertia compared with small particles, which traveled with airflow and settled behind the nozzle. The dust accumulated close to the dispersion nozzle faster than behind the nozzle location. However, specific attention must be paid to small particles, because they are more likely to cause an explosion, as their minimum explosive concentration is lower than that of large particles.</p> <p>The light extinction coefficients of cornstarch, grain dust, and sawdust were measured using a two-target method. The suspended dust concentration was measured using a calibrated laser instrument. The light extinction coefficient was linearly related to the suspended dust concentration. The correlation coefficient between the light extinction coefficient and suspended dust concentration depended on particle size, particle shape, and chemical properties. </p> <p>Controlling dust cloud generation and minimizing the concentration and volume of dust clouds are some key measures to prevent dust explosions. The mathematical models developed in this study to predict dust dispersion, suspension, and rate of settling will help solve a few of the challenges in the particulate material handling and processing industry. This method of measuring the light extinction coefficient can be applied development of a dust safety monitoring system. The result presented in this dissertation will help the industry prevent the formation of an explosive atmosphere.</p><br><p></p>

Over the past century, dust emissions have increased in frequency and intensity due to anthropogenic influences and extended droughts. Dust transports microbes, nutrients, heavy metals and other materials that may then change the biogeochemistry of the receiving environments. The purpose of this study was to find whether unique bacterial communities may provide distinct fingerprints of dust sources in the Western USA. We collaborated with the National Wind Erosion Research Network (NWERN) to identify bacterial core communities (core) of dust from ten NWERN sites, and compared communities to location, soil, and regional characteristics. In order of importance, precipitation levels (F = 43, P = 0.0001, Df = 2, r2 = 0.25), location (F = 16, P = 0.0001, Df = 5, r2 = 0.23), soil texture (F = 14, P = 0.0001, Df = 3, r2 =0.12), seasonality (F = 11, P = 0.0001, Df = 2, r2 = 0.064), and elevation (F = 5.7, P = 0.0002, r2 = 0.033) determined bacterial community composition. Bacterial core communities were defined as taxa present in at least 50% of samples at each site and offered predictable patterns of dust communities in terms of abundant (> 1% relative abundance) and rare (< 1% relative abundance) signatures. We found distinct bacterial core communities that reflected dust source systems, for example, sites contaminated with heavy metals contained Romboutsia, Turicibacter, Clostridium sensu stricto 1, Geodermatophilus, and Microvirga. Sites with association to plants and biocrusts contained Methylobacterium-Methylorubrum, Bradyrhizobium, Paenibacillus thermoaerophilus, Cohnella, and bacterial families Solirubrobacteraceae, Sphingobacteraceae, and Myxococcaceae. The presence of Sphingomonas, Stenotrophomonas, Rhodococcus, and Phenylobacterium were found in hydrocarbon contaminated soils. High stress (UV radiation and desiccation) sites contained Deinococcus, Blastococcus, and Modestobacter. We found that seasonal changes affected microbial community composition in five NWERN sites (CPER, HAFB, Jornada, Red Hills, and Twin Valley) (p < 0.05), while no seasonal effects on bacterial distribution were observed at Moab. Our results identify that the use of core microbiomes may offer a fingerprinting method to identify dust source regions.

Continuous personal dust monitors (CPDMs) are widely used to monitor respirable coal mine dust (RCMD) to reduce miners' exposures, but they are unable to directly assess respirable crystalline silica (RCS) concentrations, which are linked to the recent rise of respiratory diseases among coal miners. This incompatibility is due to the composition of the CPDM's internal filter stub. The stub consists of a fibrous borosilicate filter attached to a polypropylene (PP) backing and a polytetrafluoroethylene (PTFE) binder, which interferes with standard analytical techniques. This study developed a method for indirect analysis of dust collected on the CPDM filter stub using portable direct-on-filter Fourier Transform infrared spectroscopy (DOF-FTIR) to rapidly quantify quartz, the primary analyte of silica in coal mines. The research consisted of four studies that developed and evaluated a three-step process for dust recovery, deposition, and analysis. These studies investigated techniques for separating dust from the CPDM filter media, compared mechanisms for dust deposition onto various substrates, and assessed the ability of FTIR and scanning electron microscopy with energy dispersive X-ray (SEM-EDX) to analyze the mineral characteristics of recovered dust. The resulting method involves submerging CPDM filter stubs in 5 mL of isopropyl alcohol (IPA) and shaking them for 1 minute, followed by deposition of the dust onto a 25-mm polyvinyl chloride (PVC) filter using a syringe-based system. The PVC filter was then scanned at four 8-mm offset locations at 90° intervals from the center. Evaluating this method using field and lab-generated CPDM filter stubs revealed low dust recovery from the stubs. It was also observed that results tended to underpredict the quartz mass as the total sample mass increased. Though adjustments for recovery can be made using a scale and the method can be limited to lower mass samples, more efforts can be made to investigate better dust recovery and improve quartz determination of the samples to increase confidence in the method. / Doctor of Philosophy / To reduce respiratory diseases among coal miners, US regulation requires dust sampling in underground coal mines to monitor the total respirable coal mine dust (RCMD) concentration miners are exposed to using a specific device, the continuous personal dust monitor (CPDM). However, the CPDM cannot be used to directly differentiate the characteristics of the dust, particularly silica, which is particularly hazardous. To do this, a method to indirectly analyze the dust collected on the CPDM's internal filter stub has been evaluated using a three-step method to recover the dust, deposit the dust onto a different filter type, and then analyze the dust using a spectrometer to determine the silica mass. Four studies were performed to develop the full method. These studies investigated how dust can be recovered from filters, how to deposit dust onto another filter, and how to then analyze the dust to determine its characteristics. This was done using multiple methods to determine the optimum three-step method to quantify the silica mass in the recovered dust. The studies ultimately developed a method involving submerging the CPDM filter stub in 5 mL of isopropyl alcohol (IPA) and shaking it for 1 minute to dislodge the dust. Then, the recovered dust was deposited on a 25-mm polyvinyl chloride (PVC) filter using a syringe. After deposition, the PVC filter was finally scanned at four 8-mm offset locations at 90° intervals from the center of the filter. These scans were then used to determine the silica mass. After testing this three-step method on field and lab-generated CPDM filter stubs, results showed low dust recovery from the stubs. It was also observed that results tended to underpredict the silica mass as the total RCMD mass increased. Although the dust left behind on the filter can be determined using a scale and the method can be limited to samples with smaller masses to avoid underpredicting the quartz mass, more work can be done to improve dust recovery, improve the silica determination, and put more confidence in the method.

Dust is an almost ubiquitous component of the cosmic plasma (e.g., planetary and cometary magnetospheres, the heliosphere, the interstellar medium, supernova shells). However, it can be also frequently encountered in industrial applications as a principal agent in material treatments, or as an undesirable ingredient in a production of microelectronic components, or in fusion devices. Since dust particles are one of the main elements of interest in the solar system (e.g., Earth, Jovian and Saturnian systems) and in the interstellar medium, there is a number of missions (e.g., ROSETTA, Cassini) that provided investigations of the properties and global dynamics of charged dust grains. In these environments, the relevant charging processes are interactions with electrons and ions of the solar wind and photoemission by solar UV radiation that often dominates. However, in-site investigations of such processes are difficult because several processes act in accord. The present thesis studies charging processes in laboratory settings where these processes can be investigated separately. In the first series of experiments focused on applications in the lunar or planetary surroundings, a single (charged) dust grain is stored in an electrodynamic trap and expose to electron and/or ion beams with variable energies and...