Understanding toxicity associated with boron nitride nanotubes: Review of toxicity studies, exposure assessment at manufacturing facilities, and read-across.

Boron nitride nanotubes (BNNT) are produced by many different methods leading to variances in physicochemical characteristics and impurities in the final product. These differences can alter the toxicity profile. The importance of understanding the potential pathological implications of this high aspect ratio nanomaterial is increasing as new approaches to synthesize and purify in large scale are being developed. In this review, we discuss the various factors of BNNT production that can influence its toxicity followed by summarizing the toxicity findings from in vitro and in vivo studies conducted to date, including a review of particle clearance observed with various exposure routes. To understand the risk to workers and interpret relevance of toxicological findings, exposure assessment at manufacturing facilities was discussed. Workplace exposure assessment of BNNT from two manufacturing facilities measured boron concentrations in personal breathing zones from non-detectable to 0.95 µg/m3 and TEM structure counts of 0.0123 ± 0.0094 structures/cm3, concentrations well below what was found with other engineered high aspect ratio nanomaterials like carbon nanotubes and nanofibers. Finally, using a purified BNNT, a "read-across" toxicity assessment was performed to demonstrate how known hazard data and physicochemical characteristics can be utilized to evaluate potential inhalation toxicity concerns.

Characterizing workforces exposed to current and emerging non-carbonaceous nanomaterials in the U.S.

OBJECTIVE: Toxicology studies suggest that exposure to certain types of engineered nanomaterials (ENMs) may cause adverse health effects, but little is known about the workforce in the United States that produces or uses these materials. In addition, occupational exposure control strategies in this industry are not well characterized. This study identified U.S. ENM manufacturers and users (other than carbon nanotubes and nanofibers, which have been characterized elsewhere), determined workforce size, characterized types and quantities of materials used, occupational exposure control strategies, and the feasibility of occupational ENM exposure studies. METHODS: Eligible companies were identified and information was collected through phone surveys on nanomaterials produced or used, workforce size, location, work practices, and exposure control strategies. The companies were classified into groups for additional examinations. RESULTS: Forty-nine companies producing or using ENMs in the U.S. were identified. These companies employed at least 1,500 workers. Most companies produced or used some form of nanoscale metal. More than half of the eligible companies were suppliers for the coatings, composite materials, or general industries. Each company provided information about worker exposure reduction strategies through engineering controls, administrative controls, or personal protective equipment. Production-scale companies reported greater use of specific exposure control strategies for ENMs than laboratory-scale companies. CONCLUSIONS: Workplaces producing or using ENMs report using engineering and administrative controls as well as personal protective equipment to control worker exposure. Industrywide exposure assessment studies appear feasible due to workforce size. However, more effort must be taken to target industries using specific ENMs based on known toxicological effects and health risks.

A study update of mortality in workers at a phosphate fertilizer production facility.

OBJECTIVE: To evaluate the mortality experience among 3,199 workers employed 1951-1976 at a phosphate fertilizer production plant in central Florida with follow-up through 2011. METHODS: Cause-specific standardized mortality ratios (SMRs) for the full cohort were calculated with the U.S. population as referent. Lung cancer and leukemia risks were further analyzed using conditional logistic regression. RESULTS: The mortality due to all-causes (SMR = 1.07, 95% confidence interval [CI] 1.02-1.13, observed deaths [n] = 1,473), all-cancers (SMR = 1.16, 95%CI 1.06-1.28, n = 431), and a priori outcomes of interests including lung cancer (SMR = 1.32, 95%CI = 1.13-1.53, n = 168) and leukemia (SMR = 1.74, 95%CI = 1.11-2.62, n = 23) were statistically significantly elevated. Regression modeling on employment duration or estimated radiation scores did not show exposure-response relation with lung cancer or leukemia mortality. CONCLUSION: SMR results showed increased lung cancer and leukemia mortality in a full cohort of the phosphate fertilizer production facility. There was, however, no exposure-response relation observed among cases and matched controls.

Reducing ultrafine particulate emission from multiple 3D printers in an office environment using a prototype engineering control.

Recent studies have shown that high concentrations of ultrafine particles can be emitted during the 3D printing process. This study characterized the emissions from different filaments using common fused deposition modeling printers. It also assessed the effectiveness of a novel engineering control designed to capture emissions directly at the extruder head. Airborne particle and volatile organic compound concentrations were measured, and particle emission rates were calculated for several different 3D printer and filament combinations. Each printer and filament combination was tested inside a test chamber to measure overall emissions using the same print design for approximately 2 h. Emission rates ranged from 0.71 × 107 to 1400 × 107 particles/min, with particle geometric mean diameters ranging from 45.6 to 62.3 nm. To assess the effectiveness of a custom-designed engineering control, a 1-h print program using a MakerBot Replicator+ with Slate Gray Tough polylactic acid filament was employed. Emission rates and particle counts were evaluated both with and without the extruder head emission control installed. Use of the control showed a 98% reduction in ultrafine particle concentrations from an individual 3D printer evaluated in a test chamber. An assessment of the control in a simulated makerspace with 20 printers operating showed particle counts approached or exceeded 20,000 particles/cm3 without the engineering controls but remained at or below background levels (< 1000 particles/cm3) with the engineering controls in place. This study showed that a low-cost control could be added to existing 3D printers to significantly reduce emissions to the work environment.

Exposures during wet production and use processes of nanomaterials: a summary of 11 worksite evaluations.

From 2011-2015, the National Institute for Occupational Safety and Health Nanotechnology Field Studies Team conducted 11 evaluations at worksites that either produced engineered nanomaterials (ENMs) via a wet process or used ENMs in a wetted, suspended, or slurry form. Wet handling or processing of ENMs reduces potential exposure compared to dry handling or processing; however, air sampling data indicated exposures may still occur. Information was gathered about each company, production processes, ENMs of interest, and control measures. Exposure assessments included air sampling using filter media, surface wipe sampling, and real-time particle counting by direct-reading instruments. Electron microscopy analysis of air filters confirmed the presence of ENMs of interest (10 of 11 sites). When a method was available, chemical analysis of filters was also used to detect the presence of ENMs (nine of 11 sites). Wipe samples were collected at four of the 11 sites, and, in each case, confirmed the presence of ENMs on surfaces. Direct-reading data showed potential nanomaterial emissions (nine of 11 sites). Engineering controls included fume hoods, cleanrooms, and enclosed processes. Personal protective equipment was required during all 11 evaluations. Recommendations to address potential exposures were provided to each company following the hierarchy of controls.