Semiconductor Nanomaterials: Toxicology, Exposure Assessment, Controls & Control Banding
Kincaid*, Linda ; Rohm, Timothy
(Industrial Hygiene Services, San Jose, CA)
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Toxicology: Nanoparticles (NP) present a greater health risk than do their bulk counterparts. NP can lead to tissue inflammation, which can be a precursor of cancer. Carbon nanotubes can induce granulomas, similar to those caused by asbestos. Many NP contain metal catalysts with little relevant toxicological data. Available data are primarily based on in vitro or animal studies, with very little human toxicology. Current research indicates that total surface area or total particle count may be better exposure indices than mass concentration, the usual industrial hygiene metric. Exposure Assessment: Standard exposure assessment methodologies are inadequate for NP. Industrial hygiene methods typically measure mass concentration, which does not correlate well with NP toxicity. Commercially available instruments can measure total surface area and total particle number, but these instruments include larger particles in their measurements as well as NP. Particle counters can also be prohibitively expensive, and most are cumbersome for field measurements. Engineering Controls & PPE: Standard containment and controls are effective for NP. Laboratory hoods, glove boxes, and local exhaust ventilation effectively capture NP. HEPA filters are adequate to remove NP from an airstream. Respirators with HEPA cartridges provide effective personal protection. Latex gloves provide only moderate protection. Control Banding: Given the lack of traditional industrial hygiene methods for NP exposure assessment, control banding is a plausible interim alternative. Samuel Paik, et.al. of Lawrence Livermore National Laboratories have produced a Control Banding Nanotool that is user friendly and provides recommendations on engineering controls and PPE for various NP use scenarios. The Nanotool is based on Microsoft Excel, and it is readily customized for specific situations. Implementation of the 4 by 4 matrix is similar to the COSHH Essentials, used in Great Britain. Severity determination evaluates surface chemistry, particle shape, particle diameter, solubility, carcinogenicity, and other attributes of the NP in question. Probability determination estimates amount of materials used in a task, dustiness/mistiness, number of employees exposed, frequency of operation, and duration of operation. Each factor is entered into the Excel spreadsheet, which returns a Risk Level (RL) and recommended controls for the task in question. The CB Nanotool is presented with permission of the authors.