Airborne Samples Research Articles

Levels of Pesticides and Polychlorinated Biphenyls in Selected Homes in the Bangkok Metropolitan Region, Thailand

Past uses of hazardous chemicals in Thailand for agricultural and household purposes have resulted in their ubiquity in the environment. This study aims to characterize the levels of 41 target chemicals, including 25 organochlorine pesticides (OCP), of which 17 are persistent organic pollutant (POP) pesticides, 7 pyrethroids, and 9 polychlorinated biphenyls (PCBs) in 8 homes in the Bangkok Metropolitan Region (BMR). The study is the first of these types for Thailand, and was conducted during the dry season of 2006-2007. Samples were collected at three areas of the BMR, including urban, suburban, and rural for indoor and outdoor (I/O) air, as well as from deposits on floor surfaces. Airborne samples were taken over 24 h for both the gaseous and particulate matter phases and analyzed separately by GC-ECD following the U.S. EPA TO-10A method. Overall 35 out of 41 compounds were detected in the samples. The compounds were mostly detected and at higher levels in the gas phase, except for a few less volatile compounds, such as pyrethroids or DDT. Indoor air concentrations are higher than the outdoor levels for most chemicals; hence, the I/O ratios are mostly above 1.0, especially for rural homes. Among the OCPs, heptachlor was found at the highest concentrations for urban homes (5.2 +/- 3.1 ng/m(3) indoor and 2.6 +/- 0.4 ng/m(3) outdoor). PCB profiles were dominated by the lighter congeners, with the highest levels found for PCB31 (10.4 indoors in urban homes (ng/m(3))). Suspended matters were found to be high indoors in the rural homes, which may be linked to high-strength of indoor sources.

Simultaneous determination of chlorothalonil and its metabolite 4-hydroxychlorothalonil in greenhouse air: Dissipation process of chlorothalonil

An analytical method was developed and tested for the simultaneous determination of chlorothalonil and its main metabolite 4-hydroxychlorothalonil, in airborne samples. High performance liquid chromatography equipped with Ultra-violet detector was used to separate and quantify the analytes. Glass microfibre filters for the collection of the analytes’ particles were tested. Solid sorbents, such as Tenax, Florisil, XAD-2 and silica gel, were studied to find out the most suitable material for the collection of the analytes in the gas phase. The results have shown that only chlorothalonil was trapped in the vapor phase with highest results obtained when silica gel was the sorbent of choice. Linearity was demonstrated in a wide concentration range 0.01–10.00mgL−1. Recoveries from spiked glass microfibre filters and silica gel cartridges for chlorothalonil and 4-hydroxychlorothalonil were almost quantitative. The quantification limits were calculated to be 8.4 and 19.6ngm−3 in air for chlorothalonil and 4-hydroxychlorothalonil, respectively. The two analytes spiked on the GF/A filters and silica gel cartridges were proven to be stable for more than 15 days, at 4oC and ambient temperature. The applicability of the present method was demonstrated by the analysis of the chlorothalonil and its metabolite in greenhouse air.

Extraction and Optical Fluorescence Method for the Measurement of Trace Beryllium in Soils

Beryllium metal and beryllium oxide are important industrial materials used in a variety of applications in the electronics, nuclear energy, and aerospace industries. These materials are highly toxic, they must be disposed of with care, and exposed workers need to be protected. Recently, a new analytical method was developed that uses dilute ammonium bifluoride for extraction of beryllium and a high quantum yield optical fluorescence reagent to determine trace amounts of beryllium in airborne and surface samples. The sample preparation and analysis procedure was published by both ASTM International and the National Institute for Occupational Safety and Health (NIOSH). The main advantages of this method are its sensitivity, simplicity, use of lower toxicity materials, and low capital costs. Use of the technique for analyzing soils has been initiated to help meet a need at several of the U.S. Department of Energy legacy sites. So far this work has mainly concentrated on developing a dissolution protocol for effectively extracting beryllium from a variety of soils and sediments so that these can be analyzed by optical fluorescence. Certified reference materials (CRM) of crushed rock and soils were analyzed for beryllium content using fluorescence, and results agree quantitatively with reference values.

Concentration Profiles of AirborneMycobacterium tuberculosisin a Hospital

Pulmonary tuberculosis remains one of the major public health issues worldwide. However, concentration profiles of airborne Mycobacterium tuberculosis in hospitals and other medical facilities have not been well characterized. Therefore, the aim of the present study was to measure concentration profiles of airborne M. tuberculosis in a hospital including TB-patient related areas (TB-areas), and non-TB-patient related areas (non-TB-areas). A total of 58 airborne samples were collected by a filter and quantified by real-time qPCR system. It was found that the airborne M. tuberculosis concentrations in TB-areas were significantly higher than those in non-TB-areas. In regard to the profiles in the investigated hospital, the airborne M. tuberculosis concentrations from high to low were found in the waiting rooms and consulting rooms of medical department, emergency department, medical wards, main registry area, waiting rooms of ophthalmology department, and dining hall, respectively. In the medical wards area, it was found that the airborne M. tuberculosis concentrations in the room of a suspected TB patient were even higher than those found in negative pressure isolation rooms with TB patient. This suspected TB patient was, in fact, diagnosed as a TB patient a month later. In conclusion, concentration profiles of airborne M. tuberculosis in hospital environments were successfully characterized in our present study. In addition, it was strongly demonstrated that TB-areas do have higher airborne M. tuberculosis concentrations than non-TB-areas and implicate higher risks for nosocomial TB infection. Moreover, environmental monitoring of airborne M. tuberculosis might provide an early indicator for identification of TB patient.

Aerosol sampling by annular aspiration slots

Annular aspiration slots were studied in laboratory conditions in order to investigate their performance in sampling airborne particles. The sampling efficiency was measured in a wind tunnel as a function of particle aerodynamic diameter in various conditions of external wind speed. The geometric parameters of the annular slot and the aerodynamic conditions of sampling were optimised in order to improve the sampling efficiency. Optimal selection of these parameters led to the sampling efficiency decreasing very slightly with increasing particle size. Two semi-empirical models of sampling efficiency--in moving and calm air conditions--were derived and experimentally checked. Omnidirectional annular sampling heads are less sensitive to the external wind and their inner particle losses can be minimised. A prototype of a personal aerosol sampler for exposure assessment in occupational safety and health was designed on the basis of these models. It broadly meets the conventional efficiency for inhalable aerosol sampling.

Analysis of airborne and waterborne particles around a taconite ore processing facility

Since the mid-1970s, samples of airborne and waterborne fibrous particulates have been collected in the area of the Northshore Taconite Ore Processing Facility by the Minnesota Department of Health (MDH), the Minnesota Pollution Control Agency (PCA), and the University of Minnesota. Indirect sample preparation has consistently been used although other aspects of the sampling methods and sites have varied and analytical procedures were altered over time as more accurate and precise microscopy methods were developed (i.e., phase contrast optical microscopy, transmission electron microscopy, transmission electron microscopy with energy dispersive spectroscopy). In the mid-1970s, levels of airborne fibrous particulate in the Silver Bay area averaged from 0.00030 to 0.03 f/ml. This level was significantly greater than levels of similar particulates in the St. Paul, MN area, although two of the Silver Bay sampling sites, considered individually, did not indicate levels of fibrous particulate markedly different than that seen in St. Paul. More recent sampling data (i.e., 1990–2001) indicate mean concentration of airborne fibrous particulates (amphibole-like fibrous particulates) of 0.0020 f/ml with a range of values from 0.0001 to 0.0140 f/ml. Such levels are not significantly different from those seen in other non-urban environments in the US and Europe. Concentrations of fibrous particulates in water samples were higher in the mid-1970 when iron ore tailings were being deposited in Lake Superior, but since the tailings have been deposited on land waterborne levels of fibrous particulate in the Beaver River have remained relatively constant averaging in the range of 7.5 MFL. This level is only slightly in excess of the current EPA drinking water standard for fibrous particulates. Review and consideration of this data is important in determining the potential health risks associated with airborne and waterborne fibrous particulates in the areas of the Northshore Taconite Ore Processing Facility.

Metal Content in Air Samples Collected in an Urban Zone in Tampico, México: A First Survey

ABSTRACT With the aim to know possible risks to the population, Cd, Co, Cr, Cu, Mn, Ni, Pb, and Tl were determined for the first time in airborne samples of particulate matter in an urban zone in Tampico, México, during the winter of 2003. The 24-hour PM10 samples were collected every 6 days on quartz-filters by using a high volume sampler and analyzed by Inductively Coupled Plasma Optical Emission Spectrometer. Standard reference material was used to verify metal recovery. The maximum PM10 and lead concentrations were 12.05 and 0.040 μ g/m3, respectively, not exceeding Méxican standard values. The greatest metal concentration was that of manganese with 0.90 μ g/m3, followed by Cu and Ni with 0.17 and 0.012 μ g/m3, respectively. Agglomerates, well-defined particles, and heavy metals (e.g., Mn and Cu) were found in PM10 using Scanning Electron Microscopy and Energy Dispersive Spectroscopy. Meteorological conditions associated with the sampling period showed that Pb and Ni are being continuously emitted, and that Mn, Cu, and Co could come from one industry located to the WSW of the region. All of these concentrations do not constitute a potential risk to human health, although it is necessary to continue studying the high concentrations of Mn and Cu in longer sampling periods.

Evaluation of Quantification Methods of Occupational Endotoxin Exposure

Endotoxin has been identified as important component of organic-dust exposure and is suspected as main cause of work-related adverse health effects in dusty areas. Although the determination of endotoxin levels by using the Limulus amoebocyte lysate (LAL) assay is internationally accepted, reliability and variation of values measured with this test remain a point of discussion. Therefore, the purpose of the study was to determine the influence of different parameters on endotoxin activity measured in airborne samples. This study thus analyzed: (a) dust filter extraction procedures, (b) storage of samples, (c) usage of different commercially available LAL assays, and (d) results of the whole blood assay (WBA) compared to the LAL test. Using a parallel sampler, 120 filters were loaded with dust at 4 different occupational settings and extracted in 2 labs using a standardized protocol. Parameters like Tween in the extraction medium, extraction volume, centrifugation speed, and material of tubes used for extraction were tested. The LAL test and the WBA were able to determine the differences in dust load of filters obtained from the settings investigated. In addition, results varied significantly with modifications in extraction procedures. Using Tween for filter extraction mainly influenced the resulting endotoxin activity. In addition, LAL test differences according to manufacturer of LAL test, extraction volume, and whether the samples are freshly processed or frozen also resulted in significant variations in the endotoxin levels. In conclusion, a reliable assessment of exposure to endotoxin activity is only possible if standard operation procedures (SOPs) for sampling and determination are established.

Relative Congener Scaling of Polychlorinated Dibenzo-p-dioxins and Dibenzofurans to Estimate Building Fire Contributions in Air, Surface Wipes, and Dust Samples

The United States Environmental Protection Agency collected ambient air samples in lower Manhattan for about 9 months following the September 11, 2001 World Trade Center (WTC) attacks. Measurements were made of a host of airborne contaminants including volatile organic compounds, polycyclic aromatic hydrocarbons, asbestos, lead, and other contaminants of concern. The present study focuses on the broad class of polychlorinated dibenzo-p-dioxins (CDDs) and dibenzofurans (CDFs) with specific emphasis on the 17 CDD/CDF congeners that exhibit mammalian toxicity. This work is a statistical study comparing the internal patterns of CDD/CDFs using data from an unambiguous fire event (WTC) and other data sets to help identify their sources. A subset of 29 samples all taken between September 16 and October 31, 2001 were treated as a basis set known to be heavily impacted by the WTC building fire source. A second basis set was created using data from Los Angeles and Oakland, CA as published by the California Air Resources Board (CARB) and treated as the archetypical background pattern for CDD/CDFs. The CARB data had a congener profile appearing similar to background air samples from different locations in America and around the world and in different matrices, such as background soils. Such disparate data would normally be interpreted with a qualitative pattern recognition based on congener bar graphs or other forms of factor or cluster analysis that group similar samples together graphically. The procedure developed here employs aspects of those statistical methods to develop a single continuous output variable per sample. Specifically, a form of variance structure-based cluster analysis is used to group congeners within samples to reduce collinearity in the basis sets, new variables are created based on these groups, and multivariate regression is applied to the reduced variable set to determine a predictive equation. This equation predicts a value for an output variable, OPT: the predicted value of OPT is near zero (0.00) for a background congener profile and near one (1.00) forthe profile characterized by the WTC air profile. Although this empirical method is calibrated with relatively small sets of airborne samples, it is shown to be generalizable to other WTC, fire source, and background air samples as well as other sample matrices including soils, window films and other dust wipes, and bulk dusts. However, given the limited data set examined, the method does not allow further discrimination between the WTC data and the other fire sources. This type of analysis is demonstrated to be useful for complex trace-level data sets with limited data and some below-detection entries.

Exposición laboral a hongos y bacterias ambientales en una planta de selección de residuos de envases

Several studies have showed an association between the work in waste treatment plants and occupational health problems such as irritation of skin, eyes and mucous membranes, pulmonary diseases, gastrointestinal problems and symptoms of organic dust toxic syndrome (ODTS). These symptoms have been related to bioaerosol exposure. The aim of this study was to investigate the occupational exposure to biological agents in a plant sorting source-separated packages (plastics materials, ferric and non-ferric metals) household waste. Airborne samples were collected with M Air T Millipore sampler. The concentration of total fungi and bacteria and gram-negative bacteria were determined and the most abundant genera were identified. The results shown that the predominant airborne microorganisms were fungi, with counts greater than 12,000 cfu/m(3) and gram-negative bacteria, with a environmental concentration between 1,395 and 5,280 cfu/m(3). In both cases, these concentrations were higher than levels obtained outside of the sorting plant. Among the fungi, the predominant genera were Penicillium and Cladosporium, whereas the predominant genera of gram-negative bacteria were Escherichia, Enterobacter, Klebsiella and Serratia. The present study shows that the workers at sorting source-separated packages (plastics materials, ferric and non-ferric metals) domestic waste plant may be exposed to airborne biological agents, especially fungi and gram-negative bacteria.

Bromoform in tropical Atlantic air from 25°N to 25°S

Atmospheric mixing ratios of bromoform (CHBr3) measured over the eastern Atlantic Ocean were enhanced (4 to 13 pptv) between 8–25°N, 17–21°W, in air masses advected over the NW African coast/upwelling zone. The highest mixing ratios at 8–10°N were associated with a biomass burning plume from the African savannah belt. Airborne samples taken over Nigeria showed however that biomass burning here is not a source of CHBr3. Previously reported water samples taken near to the NW African upwelling zone do not support the very high levels of atmospheric CHBr3 observed, unless there is significant surface stratification of the atmospheric boundary layer. Other potential explanations include coastal macroalgae and/or sources within continental Africa. It is important to ascertain the nature of tropical sources of CHBr3 in order to establish the mechanisms of suggested feedbacks between organic bromine and climate change.

Monitoring of chromium species and 11 selected metals in emission and immission of airborne environment

Monitoring of chromium species as hexavalent chromium (Cr(VI)) and the determination of the total chromium concentration as well as the concentration of 11 selected metals (Al, Ca, Cd, Co, Cu, Fe, Mn, Ni, Pb, Sb, Zn) in industrial emission of a foundry and immission studies of the nearby airborne environment were carried out. The samples were taken as industrial exhaust directly by the outlet and as airborne sample in the environment with distances between some hundred meters and 2 km from the industrial factory. Wherefore two methods of sampling, sample pre-treatment and mass spectrometric measurement were developed and applied. With respect to different sampling duration different volumes of air were sampled and analysed. For the determination of Cr(VI) sampling in impingers (filled with carbonate-buffer) was used. A procedure of selective complex forming and extraction was developed and measured by double focussing sector field inductively coupled plasma mass spectrometry (ICP-SFMS). For the determination of the total chromium concentration as well as of 11 metals sampling was done by using quartz-filters. After microwave digestion in the medium of aqua regia the samples were analysed by quadrupole inductively coupled plasma mass spectrometry (ICP-QMS). The maximum concentration of Cr(VI)-species in emission samples was determined as 180 ng/m 3 air which is about 2% of total Cr. The lowest concentration of Cr(VI)-species in immission was determined as 0.5 ng/m 3 air.

Determination of dithiocarbamate fungicide propineb and its main metabolite propylenethiourea in airborne samples

A simple, rapid and sensitive GC–MS method for the determination of dithiocarbamate fungicide propineb [polymeric zinc propylenebis (dithiocarbamate)] and an improved HPLC procedure for the simultaneous determination of its main metabolite, propylenethiourea, and ethylenethiourea, the main metabolite of all ethylenedithiocarbamates, in airborne samples are described. The method for the analysis of propineb involves the evolution of carbon disulfide (CS 2), under acidic conditions in the presence of stannous chloride, extraction of the generated CS 2 into a layer of isooctane which is then analyzed for CS 2 content by GC–MS in SIM mode. Under the optimum conditions, the retention time of CS 2 was 1.89 min and the total time of chromatographic analysis was 5 min. Recoveries from spiking glass microfibre filters (GF/A) and silica gel filters were 86 ± 7 ( n = 9) and 89 ± 4 ( n = 9), respectively. The limit of detection is 0.7 ng per filter, which is equivalent to about 0.8–1.0 ng m −3 in air. In parallel, an HPLC method with ultraviolet detection is presented for the simultaneous analysis of the metabolites. Separation of the two metabolites was attained in less than 5 min. Recoveries from spiking GF/A and silica gel filters for ethylenethiourea were 100 ± 1 ( n = 3) and 98 ± 2 ( n = 3), respectively, while for propylenethiourea were 102 ± 1 ( n = 3) and 98 ± 1 ( n = 3), respectively. The detection limits are about 36–43 and 40–49 ng m −3 in air for ethylenethiourea and propylenethiourea, respectively. All the analytes spiked in the filters are proven to be stable for more than one month, at −4 °C.

Separation of V(V)-4-(2-pyridylazo)resorcinolato Complex from a Large Excess Reagent Using an ODS Cartridge for High-Performance Liquid Chromatography

A selective off-line preconcentration technique for the V(V) complex with 4-(2-pyridylazo)resorcinol has been developed and successfully applied to the determination of V(V) in an air-borne sample. The target complex was separated from excess reagent using an ODS cartridge and water as the eluent. The complex was then concentrated on another ODS cartridge using tetrabutylammonium bromide and eluted with methanol; the eluate was applied to a one-drop concentration/HPLC. A detection limit as low as (6.05 +/- 0.82)x 10(-11) M (5 ppt) was achieved.

A holistic approach to inversion of time-domain airborne EM

A “holistic” method for simultaneously estimating conductivity and calibration models from 1-D inversion of time-domain airborne electromagnetic (AEM) data is proposed. The work extends the concept of holistic inversion that been successfully applied to frequency-domain AEM data. The entire multi-component airborne dataset and available independent conductivity and interface-depth data are simultaneously inverted. A spline-based conductivity model covering the complete survey area is estimated. Unmonitored elements of the system geometry are included as unknown parameters of the calibration model and are solved for in the inversion.Conventional 1-D inversion methods invert each airborne sample in isolation from other samples. However, by simultaneously considering all of the available information together in a holistic inversion formulation, we are able to exploit the inter-component and spatial coherency characteristics of the airborne data. The formulation ensures that the conductivity and calibration models are optimal with respect to the airborne data and prior information.

Use of portable microbial samplers for estimating inhalation exposure to viable biological agents

Portable microbial samplers are being increasingly used to determine the presence of microbial agents in the air; however, their performance characteristics when sampling airborne biological agents are largely unknown. In addition, it is unknown whether these samplers could be used to assess microbial inhalation exposure according to the particle sampling conventions. This research analyzed collection efficiencies of MAS-100, Microflow, SMA MicroPortable, Millipore Air Tester, SAS Super 180, BioCulture, and RCS High Flow portable microbial samplers when sampling six bacterial and fungal species ranging from 0.61 to 3.14 microm in aerodynamic diameter. The efficiencies with which airborne microorganisms were deposited on samplers' collection medium were compared to the particle inhalation and lung deposition convention curves. When sampling fungi, RCS High Flow and SAS Super 180 deposited 80%-90% of airborne spores on agar - highest among investigated samplers. Other samplers showed collection efficiencies of 10%-60%. When collecting bacteria, RCS High Flow and MAS-100 collected 20%-30%, whereas other samplers collected less than 10% of these bioparticles. Comparison of samplers' collection efficiencies with particle inhalation convention curves showed that RCS High Flow and SAS Super 180 could be used to assess inhalation exposure to particles larger than 2.5 microm, such as fungal spores. Performance of RCS High Flow sampler was also reflective of the particle lung deposition pattern when sampling both bacteria and fungi. MAS-100 and SAS Super 180 matched the total deposition curve fairly well when collecting bacterial and fungi species, respectively. For other tested samplers, we observed substantial discrepancies between their performances and particle deposition efficiencies in the lung. The results show that feasibility of applying portable microbial samplers for exposure assessment depends on a particular sampler model and microbial species.

Methods to Sample Air Borne Propagules of Aspergillus flavus

Three techniques (cyclone samplers, filter samplers and rotorods) were evaluated for sampling airborne propagules of Aspergillus flavus in a cultivated region of southwest Arizona. Analysis of variance indicated no significant difference between cyclone and filter samplers in quantity of colony forming units caught, but there was a positive correlation between catches of the three separate impaction samplers (r = 0.84–0.99, P>0.05). There was no detectable correlation between impaction sampler catches and cyclone catches (r=0.12–0.33; P>0.05). Cyclone samplers collected a dry sample that was easy to process for quantification of fungal propagules. Size of conidia of A. flavus (combined with filter retention studies) suggests that the predominant propagules caught by the cyclone sampler were conidia, rather than sclerotia or infected vegetative matter. Using a water-soluble coating, rotorods collected viable conidia of A. flavus under controlled environment conditions, but not in the field, although viable propagules of other fungi were caught, including other Aspergilli. In the desert environment the rotorods became overloaded with particles of dust if operated for more than 2 h. Where isolate culture is required, cyclone samplers are ideal for collecting airborne A. flavus propagules in dry climates.

δ13C of volatile organic compounds (VOCS) in airborne samples by thermal desorption-gas chromatography-isotope ratio-mass spectrometry (TD-GC-IR-MS)

This paper is a preliminary investigation into the use of a thermal desorption-gas chromatography-isotope ratio mass spectrometry (TD-GC-IR-MS) method to determine stable carbon isotopic compositions ( δ 13C) of low molecular-weight volatile organic compounds (VOCs) in airborne samples (e.g. industrial and car exhaust emissions) as a means of differentiating their sources in the environment. A TD-GC-IR-MS method for obtaining δ 13C of VOCs (benzene, toluene, chlorobenzene, ethylbenzene, m-xylene and propylbenzene) in air samples has been optimised, and is proven to be both reproducible and linear. The δ 13C of the VOC standards was found to be comparable (within analytical error) to that obtained from direct GC-IR-MS analysis. This novel method of VOC analysis is valuable in environmental and forensic investigations.

An Evaluation of Analytical Methods, Air Sampling Techniques, and Airborne Occupational Exposure of Metalworking Fluids

This article summarizes an assessment of air sampling and analytical methods for both oil and water-based metalworking fluids (MWFs). Three hundred and seventy-four long-term area and personal airborne samples were collected at four plants using total (closed-face) aerosol samplers and thoracic samplers. A direct-reading device (DustTrak) was also used. The processes sampled include steel tube making, automotive component manufacturing, and small part manufacturing in a machine shop. The American Society for Testing and Materials (ASTM) Method PS42-97 of analysis was evaluated in the laboratory. This evaluation included sample recovery, determination of detection limits, and stability of samples during storage. Results of the laboratory validation showed (a) the sample recovery to be about 87%, (b) the detection limit to be 35 μg, and (c) sample stability during storage at room temperature to decline rapidly within a few days. To minimize sample loss, the samples should be stored in a freezer and analyzed within a week. The ASTM method should be the preferred method for assessing metalworking fluids (MWFs). The ratio of thoracic aerosol to total aerosol ranged from 0.6 to 0.7. A similar relationship was found between the thoracic extractable aerosol and total extractable aerosol. The DustTrak, with 10-μm sampling head, was useful in pinpointing the areas of potential exposure. MWF exposure at the four plants ranged from 0.04 to 3.84 mg/m 3 with the geometric mean ranging between 0.22 to 0.59 mg/m 3 . Based on this data and the assumption of log normality, MWF exposures are expected to exceed the National Institute for Occupational Safety and Health recommended exposure limit of 0.5 mg/m 3 as total mass and 0.4 mg/m 3 as thoracic mass about 38% of the time. In addition to controlling airborne MWF exposure, full protection of workers would require the institution of programs for fluid management and dermal exposure prevention.

Crystalline Silica Analysis: A Comparison of Calibration Materials and Recent Coal Mine Dust Size Distributions

Abstract Since 1982 standard calibration materials recommended for respirable crystalline silica analysis by the Mine Safety and Health Administration (MSHA) P7 Infrared Method and the National Institute for Occupational Safety and Health (NIOSH) X-ray Diffraction (XRD) Analytical Method 7500 have undergone minor changes in size distribution. However, a critical assumption has been made that the crystalline silica in ambient mine atmosphere respirable dust samples has also remained essentially unchanged in particle size distribution. The objective of this work, therefore, is to compare recent particle size distributions of underground coal mine dust and the silica component of these dusts with estimated aerodynamic particle size distributions of calibration standard materials MIN-U-SIL 5, Berkeley 5, and SRM 1878 used by two crystalline silica analysis techniques. This work provides resolution to a previously reported discrepancy involving the proper sample dilution for the particle sizing method used. Dust impactor sampling data for various locations in 13 underground coal mines were collected between 1991 and 1998 and analyzed for the respirable mass median aerodynamic diameters. The data suggest that the MSHA P7 Method will underestimate the silica content of the sample by at most 8.5 % in the median size range of 0.9–3.6 µm and that it is unlikely one would obtain any significant error in the MSHA P7 Method analysis when the method uses Berkeley 5, MIN-U-SIL 5, or SRM 1878 as a calibration standard material. The results suggest that the NIOSH Analytical Method 7500 would be more appropriate for a dust sample that is representative of the total (no cyclone classifier) rather than the respirable airborne dust, particularly since the mass fraction in the size range below 4 µm is usually a small percentage of the total airborne dust mass. However, the NIOSH Analytical Method 7500 is likely to underestimate the silica content of an airborne respirable dust sample by only 5–10%. The results of this study also suggest that any changes that may have occurred in the median respirable size of airborne coal mine dust are not significant enough to cause any appreciable error in the current methods used for respirable crystalline silica analysis.