Evaluation and Resolution of Two Sampling Methods for Airborne Aromatic Diisocyante Monomers

Details

• Personal Author:
  Schaeffer JW ; Schaeffer JW
• Description:
  Isocyanates are highly reactive electrophilic compounds used extensively for the production of a wide range of polyurethane end-use products that are indispensable to a number of industries, and also in our everyday life. Characterized by two NCO functional groups attached to an aliphatic or aromatic parent compound, isocyanates are low molecular weight compounds. Due to their reactivity, isocyanates are potent sensitizers and the leading cause of occupational asthma. Other isocyanate exposure-related health effects, such as acute irritation, bronchial hyperactivity, contact dermatitis, and hypersensitivity pnuemonitis are well recognized. The Occupational Safety and Health Administration (OSHA) has promulgated a set of ceiling Permissible Exposure Limits (PELs) of 20 parts per billion (ppb) for the most used aromatic isocyanates, methylene bispenyl isocyanate (MDI) and toluene diisocyanate (TDI). To measure airborne isocyanates, the Occupational Safety and Health Administration prescribes the use of a reagent-coated glass fiber filter that is sent to a laboratory after collection for extraction and then HPLC analysis. The measurement of airborne isocyantates presents inherent challenges and difficulties in both sampling and analysis based on their chemical and physical properties. Worker exposure to airborne isocyanates may be present in either the gas or particle phase, or both. To improve the performance of the reagent-coated glass fiber filters, field extraction of the filter has been recommended. Previous studies have identified a significant difference in the amount of MDI recovered of these two commonly used methods. This research was designed to evaluate the accuracy of extraction, or desorption, of the filter in the field and laboratory following a liquid and aerosol spiking technique. In Chapter 2, an innovative and novel isocyanate aerosol generating system (IAGS) to deliver known amounts of isocyante to test filters was evaluated. The IAGS was designed to emit a wide range of isocyaante aerosols to effectively model typical exposure scenarios encountered in polyurethane spray applications. Initial validation tests using water were completed to ensure the IAGS met design values and expectations. For example, delivery of isocyanates was accomplished by interfacing a KD Scientific 200 Two-Syringe Infusion Pump with an EZSTARTER airbrush with an atomizing nozzle from PAASCHE. The reported accuracy and reproducibility of the KD Scientific 200 Two-Syringe Infusion Pump were +/- <1% and +/- <0.1%, respectively. Dispensed flow rates of 0.193 and 0.380 ml min.-1 were validated with an experimental value of less than 1% error emitted from the IAGS. A subsequent pilot study, consisting of five samples, was conducted using an MDI working solution corresponding to 1.3 microg ml-1 of toluene dispensed at a flow rate of 0.193 ml min.-1. This pilot study was a proof of concept and not an evaluation of the GFF method. With a standard deviation of 18 nanograms (ng) and a coefficient of variation of 8%, the IAGS was concluded to exceed expectations of consistent delivery of aerosolized MDI in order to evaluate the GFF method. MDI working solutions were prepared with toluene. Therefore, toluene was examined for potential interference with isocyaante deriviatization by 1,2-PP. Toluene was determined not to interfere with the reaction between MDI and 1,2-PP based on the reported amounts of MDI following a series of dilutions with an increasing volume of toluene. Additionally, particle size distribution of the IAGS was characterized using a Grimm Dust Monitor Model 1.108. Data were approximately log-normally distributed and count median-, and mass median diameters were calculated for each MDI working solution. The number and mass of particles cm-3 was normalized to the size range collected in each channel. An interval-normalized number and mass frequency plot were constructed to summarize the distribution. Approximately 95% of the aerosol mass concentration was associated with particles greater than 2 microm while 95% of the aerosol number concentration was associated with particles less 2 microm. The majority of the number concentration (75%) was contained between 0.35 and 0.725 microm. Particles greater than 3.5 microm contained 75% of the mass during the process. Some interesting effects of particle size and MDI concentration were observed in this study. Notably, the mass median diameter decreased with increasing mass concentrations of isocyanate. Since 2 microm is the recommended upper limit for using GFFs, ideally, the MMD would have been closer to 1micro to evaluate accuracy of sampling airborne MDI and TDI. However, the IAGS has provided a basis to model future experiments that spray load filters with known amounts of isocyanate. Overall, this project demonstrated that an isocyanate aerosol generating system could be developed for the purpose of spray-loading GFFs with known amounts of analyte to evaluate accuracy. In Chapter 3, accuracy of the field (FD) and laboratory desorption (LD) methods was evaluated using a liquid spike and the IAGS from Chapter 2 to treat filters with previously underivatized technical and pure grade MDI. A range of working solutions was prepared to evaluate the FD and LD methods at small amounts of MDI. Additionally, using specific iterations of the flow rate of the syringe pump and a sampling pump, filter desorption methods were evaluated at, below, and above the OSHA PEL. A total of 191 MDI (i.e., technical and pure grade) samples were collected using FD and LD methods. Quantitative determinations of MDI from spray loading (n=105) and pipette loading (n=86) were reported in units of mass. Theoretical diisocyanate mass was calculated from the concentration of the working solution, flow rate of the syringe pump, and total sampling time. Data were log-transformed to make inferences using a ratio of observed over theoretical, or percent recovery, to evaluate the accuracy and consistency of each diisocyanate field sampling method. Using the general linear model, a statistically significant three-way interaction was detected in the application of both technical and pure grade MDI, specifcially between loading mechanism, desorption methods, and loading concentration (p-value <0.05). This three-way interaction was not unexpected. Analytical results at each concentration were conjectured to vary with desorption method and loading mechanism. These results are consistent with previous work conducted in field experiments that demonstrated that filters desorbed in the field consistently produced higher amounts of MDI. Additionally, pipette loading of free MDI onto filter was anticipated to play a pivotal role in quantitative determinations of MDI as compared to spray loading. Generally, pipette and spray loading an FD and LD filter with a solution of underivatized MDI (i.e., technical and pure grade) yielded a significantly low percent recovery. For a fixed loading, statistically significant differences were detected between FD and LD (at specific loading concentrations) when either grade of MDI was sprayed onto a filter, but not when it was liquid spiked. Consistent with other studies, FD filters consistently yielded a higher percent recovery of MDI than LD filters. The observed statistical significant difference between FD and LD results related to airborne MDI were practically relevant. Underestimations of MDI in both FD and LD filters were attributed to reactions with water vapor or other hydroxyl radicals that may be present and simultaneously collected onto the filter. However, the loss of MDI was minimized in FD filters since the extracting solvent dissolved both the derivatizing reagent and any un-reacted isocyanate, allowing the two to combine in solution and form a stable urea-derivative. The LD filters, instead, were not desorbed for at least a few days considering shipping time. MDI aerosols larger than 2 micro may have derivatized only a portion of the aerosol while the un-reacted portion was further exposed to humid air trapped inside the cassette after replacing the top cover and plugs. Using the mixed procedure in the SAS System, simple difference LSMEANs were analyzed between FD filters treated with technical and pure grade MDI, as well as LD filters. Compared to the technical grade MDI results, pure grade MDI was even further underestimated by both FD and LD filters whether they were pipette or spray loaded. The presence of other compounds in the technical grade may have partially shielded (since technical grade was still underestimated) the MDI from other reactants, facilitated dispersion of the MDI, or enhanced the analytical results. The study in Chapter 4 evaluated the suitability of immediate desorption of filters treated with aerosolized pure grade TDI, using the IAGS, as compared to desorption at the analytical laboratory. Using the same study design as Chapter 3, five TDI working solutions were prepared with toluene to determine if concentration linearly predicted the percent recovery of TDI. A total of 50 TDI samples were collected using FD and LD methods. Data were log-transformed to make inferences using a ratio of observed over theoretical. Data were balanced indicating that the factors in this model were orthogonal. Using the general linear model, the omnibus test of the model showed a significant F-value of 5.26 (p-value <0.0001), the main effect of desorption alone was not found to predict percent recovery with an F-value of 1.26. The F-value associated with concentration was 9.34 (p-value < 0.0001). Concentration was linearly related to percent recovery after accounting for desorption. Significant two-way interactions between desorption and concentration was not observed. Generally, analytical results from each loading concentration of TDI did not vary with desorption method. Differences between FD and LD sampling methods were not significant following sample collection of atomized working solutions 2-5. However, a significant difference was observed between FD and LD percent recovery of working solution 1, which emphasizes the importance of immediate desorption for a specific concentration of TDI composed of a particular fraction of gas and aerosol phases. FD and LD filters treated with atomized TDI demonstrated a statistically significant underestimation of recovered TDI compared to the theoretical amount across all working solutions. The profile of atomized TDI percent recovery was similar to the pure grade MDI results presented in Chapter 3. Loss of isocyanate to competitive reactions with water vapor most likely accounts for the low percent recovery observed in both this study and the MDI study. While volatilization of TDI may exclusively account for the loss of isocyanate (i.e., to the inside walls of the cassette), MDI has a much lower vapor pressure than TDI, and was not anticipated to volatilize during that study. As water vapor from ambient air was drawn onto the filter by the sampling pump, either hydrolysis of the isocyanate to its respective diamine occurred, or a polymeric urea was formed. As the concentration of TDI increased, the particle size distribution increased as well, causing agglomeration and less contact with the reagent-coated filter. Taken together, the three studies demonstrate that while immediate desorption of isocyanate laden filters minimizes loss of the analyte, yielding higher amounts, field desorption significantly underestimates true amounts of isocyanate. Furthermore, it appears that accuracy of these sampling methods is not only governed by timing of desorption, the presence of other reactants, and the physical state, including size, of the isocyanate, but also the composition of the formula or product being applied. Finally, the studies provide evidence that continued research on current methods, or the development of novel methods able to efficiently derivatize an isocyanate, forming a reaction product that is detected readily and accurately, are essential to protecting workers from inadvertent exposures. [Description provided by NIOSH]
• Subjects:
  Air Pollutants, Occupational Dust Environmental Monitoring Hydrocarbons Isocyanates Occupational Health Particulate Matter Safety Toluene
• Keywords:
  4,4'methylenebisphenyl Isocyanate Airborne Particles Air Sampling Techniques Aromatic Hydrocarbons Breathing Zone Diisocyanates Dust Inhalation Dust Sampling MDI Particle Size Particulate Sampling Methods Sampling Methods Toluene-2,4-diisocyanate Toluene-2,6-diisocyanate Toluenes

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• Publisher:
  Colorado State University
• Document Type:
  Text
• Funding:
  Cooperative Agreement
• Genre:
  Dissertation ; Dissertation
• Place as Subject:
  Colorado ; OSHA Region 8
• CIO:
  National Institute for Occupational Safety and Health (NIOSH) ; National Institute for Occupational Safety and Health (NIOSH)
• Topic:
  Workplace Safety & Health ; Workplace Safety & Health
• Location:
  North America ; North America
• Pages in Document:
  1-351
• NIOSHTIC Number:
  nn:20052270
• Citation:
  Fort Collins, CO: Colorado State University, 2013 Summer; :1-351
• CAS Registry Number:
  Diphenylmethane diisocyanate (CAS RN 101-68-8) ; Toluene 2,4-diisocyanate (CAS RN 584-84-9) ; Toluene 2,6-diisocyanate (CAS RN 91-08-7) ; Diphenylmethane diisocyanate (CAS RN 101-68-8) ; Toluene 2,4-diisocyanate (CAS RN 584-84-9) ; Toluene 2,6-diisocyanate (CAS RN 91-08-7)
• Federal Fiscal Year:
  2013
• NORA Priority Area:
  Agriculture, Forestry and Fishing ; Agriculture, Forestry and Fishing
• Performing Organization:
  Colorado State University - Ft. Collins
• Peer Reviewed:
  False
• Start Date:
  20030915
• Source Full Name:
  Evaluation and resolution of two sampling methods for airborne aromatic diisocyante monomers
• End Date:
  20270914
• Collection(s):
  National Institute for Occupational Safety and Health
• Main Document Checksum:
  urn:sha-512:eef6dd5bfaa02dc967bbd65771ca71284f07364bceda9791dac2d88c9a7d65a1d4f1294f29222fabee94d26d03cee0105d69c1d8469c4e563780b70f986c0759
• Download URL:
  https://stacks.cdc.gov/view/cdc/211824/cdc_211824_DS1.pdf
• File Type:
  [PDF - 5.12 MB ]