Fiber sampling technique and counting protocol development for carbon nanotubes

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PROJECT ABSTRACT The goal of this project is to develop a new method for fiber sampling. The method currently used for airborne sampling of carbon nanotubes (CNTs) is adapted from micrometer-scale asbestos sampling. To achieve our goal, we will study surface properties of different CNTs and sampling filters contributing to efficiency, develop a novel image analysis protocol with our algorithms, use a newly developed nanoparticle (NP) isokinetic diffusion sampler, simulate and elucidate the particle behavior, and produce a new method suitable to CNTs sampling. Burden: Exposure to airborne CNTs has been of highest concern following their designation as a potential human carcinogen. The potential health effects of CNTs have shown some similarity to those of asbestos fibers in animal models. CNTs global market is projected to reach $103.2 billion by 2030 with 16.3% annual growth. The fiber sampling method used for asbestos has been a recommended method for sampling CNT fibers. CNTs contain individual fibers with diameters that are one tenth to one hundredth that of asbestos fibers. The NIOSH Methods 7402 was found to be very challenging and time consuming for identifying a few very fine CNT fibers on a grid sample under electron microscopy. Questions raised by this challenge include whether the number and size of CNT fibers collected by 7402 method are representative of those in the air, whether these sizes are affected by the sampling and extensive processing required by the method, and how the exposure to fine fibers can be quantified properly to evaluate associated health effects when this method is not yet validated for CNT. Need: A new method and technique for sampling fine fibers to 1) collect fibers efficiently in the sampled air without loss, 2) directly analyze the collected fibers with minimal processing of the sample, and 3) easily count the fibers to obtain the concentration and size, which will resolve the lack of accuracy of exposure measurements and the significant time requirement of sample analysis. When used for CNTs, the collection efficiency and performance of sampling and analysis must be evaluated. It is critical to design a new sampling substrate because the currently used mixed cellulose ester (MCE) filter for collecting asbestos may not be suitable for collecting CNTs. The fibers collected on the MCE filter need to be processed for transfer to a grid for analysis, small fibers can be agglomerated or lost. A new sampling method and substrate that can effectively collect fibers to be analyzed directly will prevent the loss or change of collected fibers through the transfer process. Impact: The wide range of applications that use fiber materials such as CNTs, asbestos and fiberglass and other NPs can employ the developed protocol and method to effectively quantify the exposure level in terms of fiber/particle concentration. This information may change the current measurement metric for CNTs from mass concentration to fiber/particle number concentration. Using more precise counting can characterize the exposure concentration at a very low and difficult to measure mass concentration and provide associations to related health effects for a measurement below the current limit of mass quantification for CNTs.