Pamela L. Drake

Characterizing Exposures to Airborne Metals and Nanoparticle Emissions in a Refinery

An air quality survey was conducted at a precious metals refinery in order to evaluate worker exposures to airborne metals and to provide detailed characterization of the aerosols. Two areas within the refinery were characterized: a furnace room and an electro-refining area. In line with standard survey practices, both personal and area air filter samples were collected on 37-mm filters and analyzed for metals by inductively coupled plasma-atomic emission spectroscopy. In addition to the standard sampling, measurements were conducted using other tools, designed to provide enhanced characterization of the workplace aerosols. The number concentration and number-weighted particle size distribution of airborne particles were measured with a fast mobility particle sizer (FMPS). Custom-designed software was used to correlate particle concentration data with spatial location data to generate contour maps of particle number concentrations in the work areas. Short-term samples were collected in areas of localized high concentrations and analyzed using transmission electron microscopy (TEM) and energy dispersive spectroscopy (EDS) to determine particle morphology and elemental chemistry. Analysis of filter samples indicated that all of the workers were exposed to levels of silver above the Occupational Safety and Health Administration permissible exposure limit of 0.01 mg m(-3) even though the localized ventilation was functioning. Measurements with the FMPS indicated that particle number concentrations near the furnace increased up to 1000-fold above the baseline during the pouring of molten metal. Spatial mapping revealed localized elevated particle concentrations near the furnaces and plumes of particles rising into the stairwells and traveling to the upper work areas. Results of TEM/EDS analyses confirmed the high number of nanoparticles measured by the FMPS and indicated the aerosols were rich in metals including silver, lead, antimony, selenium, and zinc. Results of the survey were used to deduce appropriate strategies for mitigation of worker exposure to airborne metals.

Evaluation of two portable lead-monitoring methods at mining sites

Two methods for measuring airborne lead using field-portable instruments have been developed by the National Institute for Occupational Safety and Health (NIOSH): Method 7702 uses X-ray fluorescence (XRF), and Method 7701 employs ultrasonic extraction (UE) followed by anodic stripping voltammetry (ASV). The two portable methods were evaluated at mining sites. Area air samples were collected throughout two mills where ore from nearby mines was processed; the primary constituent of the ore was lead sulfide (galena). The air samples were collected on 37 mm mixed cellulose ester membrane filters housed within plastic filter cassettes. At the end of the work shift, the cassettes were collected and taken to a room off-site for analysis by the two portable methods. The filter samples were first analyzed by XRF and then by UE/ASV. Calibration was verified on both instruments according to standard procedures. The samples were then sent for confirmatory analysis via flame atomic absorption spectrometry (FAAS) according to NIOSH Method 7082. Pairwise comparisons between the methods using the paired t-test showed no statistically significant differences between ASV and FAAS (P>0.05); however, the comparison between XRF and FAAS was statistically significant (P<0.05). The elevated lead concentrations reported by XRF relative to FAAS were likely the result of the ability of XRF to report total lead, including lead silicates. This form of lead is not liberated in the digestion process prior to FAAS analysis, and is therefore not detected by this method. Despite this discrepancy, lead concentrations measured by both portable technologies were found to be highly correlated with the laboratory method (R2>0.96), suggesting that they are suitable as screening methods for airborne lead at mining sites.

Assessing mercury health effects in gold workers near El Callao, Venezuela.

Mercury exposure and health status were examined in 40 gold workers in the area surrounding El Callao, Venezuela. Concentrations of mercury in workplace air were measured on 3 successive days, and spot urine and hair samples were also taken for analysis. Subjects underwent a physical examination and completed a questionnaire regarding employment history, work activities involving mercury exposure, use of protective clothing and equipment, and frequency of 37 symptoms associated with mercury toxicity. A complete set of health data was collected for 29 of the subjects. Use of protective equipment was limited, and 17.9%, 24.1%, and 48.3% of subjects had mercury concentrations in air, hair, and urine, respectively, above contemporary occupational exposure guidelines. Physical examination found the workers to be generally healthy and without overt symptoms of mercury toxicity. The frequency of psychoneurological, gastrointestinal, cardiorespiratory, and dermal symptoms was unrelated to any of the measures of mercury exposure. Two subjects had modestly elevated urinary levels of N-acetyl &bgr;-d-glucosaminidase. Despite substantial occupational exposure to mercury among a number of the subjects, few adverse health effects were observed that were plausibly related to mercury.

Deposition Uniformity of Coal Dust on Filters and Its Effect on the Accuracy of FTIR Analyses for Silica

Miners are exposed to silica-bearing dust which can lead to silicosis, a potentially fatal lung disease. Currently, airborne silica is measured by collecting filter samples and sending them to a laboratory for analysis. Since this may take weeks, a field method is needed to inform decisions aimed at reducing exposures. This study investigates a field-portable Fourier transform infrared (FTIR) method for end-of-shift (EOS) measurement of silica on filter samples. Since the method entails localized analyses, spatial uniformity of dust deposition can affect accuracy and repeatability. The study, therefore, assesses the influence of radial deposition uniformity on the accuracy of the method. Using laboratory-generated Minusil and coal dusts and three different types of sampling systems, multiple sets of filter samples were prepared. All samples were collected in pairs to create parallel sets for training and validation. Silica was measured by FTIR at nine locations across the face of each filter and the data analyzed using a multiple regression analysis technique that compared various models for predicting silica mass on the filters using different numbers of “analysis shots.” It was shown that deposition uniformity is independent of particle type (kaolin vs. silica), which suggests the role of aerodynamic separation is negligible. Results also reflected the correlation between the location and number of shots versus the predictive accuracy of the models. The coefficient of variation (CV) for the models when predicting mass of validation samples was 4%–51% depending on the number of points analyzed and the type of sampler used, which affected the uniformity of radial deposition on the filters. It was shown that using a single shot at the center of the filter yielded predictivity adequate for a field method, (93% return, CV approximately 15%) for samples collected with 3-piece cassettes. Copyright 2013 American Association for Aerosol Research

Development of a field method for measuring manganese in welding fume

Workers who perform routine welding tasks are potentially exposed to fume that may contain manganese. Manganese may cause respiratory problems and is implicated in causing the occurrence of Parkinson-like symptoms. In this study, a field colorimetric method for extracting and measuring manganese in welding fume was developed. The method uses ultrasonic extraction with an acidic hydrogen peroxide solution to extract welding fume collected on polyvinyl chloride filters. Commercially available pre-packaged reagents are used to produce a colored solution, created by a reaction of manganese(ii) with 1-(2-pyridylazo)-2-naphthol. Absorbance measurements are then made using a portable spectrophotometer. The method detection limit and limit of quantification (LOQ) were 5.2 microg filter(-1) and 17 microg filter(-1), respectively, with a dynamic range up to 400 microg filter(-1). When the results are above the LOQ for the colorimetric method, the manganese masses are equivalent to those measured by the International Organization for Standardization Method 15202-2, which employs a strong acid digestion and analysis using inductively coupled plasma-optical emission spectrometry.

Evaluation of a standardized method for determining soluble silver in workplace air samples

Several occupational exposure limits and guidelines exist for silver, but the values for each depend on the chemical form of the silver compound in question. In the past, it generally was not possible, without prior knowledge of the work process, to distinguish soluble silver from insoluble silver compounds collected in workplace air samples. Therefore, analytical results were historically reported as total silver. In this study, work was conducted to evaluate a method to differentiate between the quantities of water-soluble silver compounds and total silver collected on filters. The investigation entailed an evaluation of an International Organization for Standardization method to determine soluble silver in airborne particulate matter. The study design incorporated laboratory experiments to evaluate analytical figures of merit, such as selection of appropriate filter media and extraction solution, analytical recovery, and sample stability during storage. Polytetrafluoroethylene (PTFE) filters (2 microm, 37 mm) in opaque cassettes were either spiked with known amounts of silver nitrate or contained a known mass of solid silver nitrate. Results showed that over 90% of the silver was recovered from PTFE filters. Also, field studies were conducted in which workplace air samples were collected in two silver refineries. Some of these samples were analyzed only for soluble silver while others were sequentially extracted and analyzed, first, for soluble silver, then for total silver. The mass fractions of soluble silver, as compared to total silver, were approximately 2% or less. This investigation served to validate an international standard procedure for the determination of soluble silver in workplace air samples.

Promoting early exposure monitoring for respirable crystalline silica: Taking the laboratory to the mine site

ABSTRACT The exposure to respirable crystalline silica (RCS) in the mining industry is a recognized occupational hazard. The assessment and monitoring of the exposure to RCS is limited by two main factors: (1) variability of the silica percent in the mining dust and (2) lengthy off-site laboratory analysis of collected samples. The monitoring of respirable dust via traditional or real-time techniques is not adequate. A solution for on-site quantification of RCS in dust samples is being investigated by the Office of Mine Safety and Health Research, a division of the National Institute for Occupational Safety and Health. The use of portable Fourier transform infrared analyzers in conjunction with a direct-on-filter analysis approach is proposed. The progress made so far, the necessary steps in progress, and the application of the monitoring solution to a small data set is presented. When developed, the solution will allow operators to estimate RCS immediately after sampling, resulting in timelier monitoring of RCS for self-assessment of compliance at the end of the shift, more effective engineering monitoring, and better evaluation of control technologies.