Product stewardship and science: Safe manufacture and use of fiber glass

Carbon nanotube pathogenicity conforms to a unified theory for mesothelioma causation by elongate materials and fibers

The purpose of this review is to elucidate how dimensional and durability characteristics of high aspect ratio nanomaterials (HARN), including carbon nanotubes (CNT) and metal nanowires (MeNW), contribute to understanding the fiber pathogenicity paradigm (FPP), including by explaining the structure-activity relationships (SAR) of a diverse range of natural and synthetic elongate materials that may or may not contribute to mesothelioma development in the lung. While the FPP was originally developed to explain the critical importance of asbestos and synthetic vitreous fiber length, width, aspect ratio and biopersistence in mesothelioma development, there are a vast number of additional inhalable materials that need to be considered in terms of pathogenic features that may contribute to mesothelioma or lack thereof. Not only does the ability to exert more exact control over the length and biopersistence of HARNs confirm the tenets of the FPP, but could be studied by implementating more appropriate toxicological tools for SAR analysis. This includes experimentation with carefully assembled libraries of CNTs and MeNWs, helping to establish more precise dimensional features for interfering in lymphatic drainage from the parietal pleura, triggering of lysosomal damage, frustrated phagocytosis and generation of chronic inflammation. The evidence includes data that long and rigid, but not short and flexible multi-wall CNTs are capable of generating mesotheliomas in rodents based on an adverse outcome pathway requiring access to pleural cavity, obstruction of pleural stomata, chronic inflammation and transformation of mesothelial cells. In addition to durability and dimensional characteristics, bending stiffness of CNTs is a critical factor in determining the shape and rigidity of pathogenic MWCNTs. While no evidence has been obtained in humans that CNT exposure leads to a mesothelioma outcome, it is important to monitor exposure levels and health effect impacts in workers to prevent adverse health outcomes in humans.

Thermal management materials for energy-efficient and sustainable future buildings

Thermal management plays a key role in improving the energy efficiency and sustainability of future building envelopes. Here, we focus on the materials perspective and discuss the fundamental needs, current status, and future opportunities for thermal management of buildings. First, we identify the primary considerations and evaluation criteria for high-performance thermal materials. Second, state-of-the-art thermal materials are reviewed, ranging from conventional thermal insulating fiberglass, mineral wool, cellulose, and foams, to aerogels and mesoporous structures, as well as multifunctional thermal management materials. Further, recent progress on passive regulation and thermal energy storage systems are discussed, including sensible heat storage, phase change materials, and radiative cooling. Moreover, we discuss the emerging materials systems with tunable thermal and other physical properties that could potentially enable dynamic and interactive thermal management solutions for future buildings. Finally, we discuss the recent progress in theory and computational design from first-principles atomistic theory, molecular dynamics, to multiscale simulations and machine learning. We expect the rational design that combines data-driven computation and multiscale experiments could bridge the materials properties from microscopic to macroscopic scales and provide new opportunities in improving energy efficiency and enabling adaptive implementation per customized demand for future buildings.

The dissolution of stone wool fibers with sugar-based binder and oil in different synthetic lung fluids

The biopersistence of fiber materials is one of the cornerstones in estimating potential risk to human health upon inhalation. To connect epidemiological and in vivo investigations with in vitro studies, reliable and robust methods of fiber biopersistence determination and understanding of fiber dissolution mechanism are required. We investigated dissolution properties of oil treated stone wool fibers with and without sugar-based binder (SBB) at 37 °C in the liquids representing macrophages intracellular conditions (pH 4.5). Conditions varied from batch to flow of different rates. Fiber morphology and surface chemistry changes caused by dissolution were monitored with scanning electron microscopy and time-of-flight secondary ion mass spectrometry mapping. Stone wool fiber dissolution rate depends on liquid composition (presence of ligands, such as citrate), pH, reaction products transport and fibers wetting properties. The dissolution rate decreases when: 1) citrate is consumed by the reaction with the released Al cations; 2) the pH increases during a reaction in poorly buffered solutions; 3) the dissolution products are accumulated; 4) fibers are not fully wetted with the fluid. Presence of SBB has no influence on dissolution rate if fiber material was wetted prior to dissolution experiment to avoid poorly wetted fiber agglomerates formation in the synthetic lung fluids.

Insulation fiber deposition in the airways of men and rats. A review of experimental and computational studies

The typical insulation rock, slag and glass wool fibers are high volume materials. Current exposure levels in industry (generally ≤ 1 fiber/cm³ with a median diameter ∼1 μm and length ≥10 μm) are not considered carcinogenic or causing other types of severe lung effects. However, epidemiological studies are not informative on effects in humans at fiber levels >1 fiber/cm³. Effects may be inferred from valid rat studies, conducted with rat respirable fibers (diameter ≤ 1.5 μm). Therefore, we estimate delivery and deposition in human and rat airways of the industrial fibers. The deposition fractions in humans head regions by nasal (∼0.20) and by mouth breathing (≤0.08) are lower than in rats (0.50). The delivered dose into the lungs per unit lung surface area during a 1-day exposure at a similar air concentration is estimated to be about two times higher in humans than in rats. The deposition fractions in human lungs by nasal (∼0.20) and by mouth breathing (∼0.40) are higher than in rats (∼0.04). The human lung deposition may be up to three times by nasal breathing and up to six times higher by oral breathing than in rats, qualifying assessment factor setting for deposition.

Toxicological and epidemiological studies on effects of airborne fibers: coherence and public [corrected] health implications

Airborne fibers, when sufficiently biopersistent, can cause chronic pleural diseases, as well as excess pulmonary fibrosis and lung cancers. Mesothelioma and pleural plaques are caused by biopersistent fibers thinner than ∼0.1 μm and longer than ∼5 μm. Excess lung cancer and pulmonary fibrosis are caused by biopersistent fibers that are longer than ∼20 μm. While biopersistence varies with fiber type, all amphibole and erionite fibers are sufficiently biopersistent to cause pathogenic effects, while the greater in vivo solubility of chrysotile fibers makes them somewhat less causal for the lung diseases, and much less causal for the pleural diseases. Most synthetic vitreous fibers are more soluble in vivo than chrysotile, and pose little, if any, health pulmonary or pleural health risk, but some specialty SVFs were sufficiently biopersistent to cause pathogenic effects in animal studies. My conclusions are based on the following: 1) epidemiologic studies that specified the origin of the fibers by type, and especially those that identified their fiber length and diameter distributions; 2) laboratory-based toxicologic studies involving fiber size characterization and/or dissolution rates and long-term observation of biological responses; and 3) the largely coherent findings of the epidemiology and the toxicology. The strong dependence of effects on fiber diameter, length, and biopersistence makes reliable routine quantitative exposure and risk assessment impractical in some cases, since it would require transmission electronic microscopic examination, of representative membrane filter samples, for determining statistically sufficient numbers of fibers longer than 5 and 20 μm, and those thinner than 0.1 μm, based on the fiber types.

Pulmonary toxicity of carbon nanotubes and asbestos - similarities and differences

Carbon nanotubes are a valuable industrial product but there is potential for human pulmonary exposure during production and their fibrous shape raises the possibility that they may have effects like asbestos, which caused a worldwide pandemic of disease in the20th century that continues into present. CNT may exist as fibres or as more compact particles and the asbestos-type hazard only pertains to the fibrous forms of CNT. Exposure to asbestos causes asbestosis, bronchogenic carcinoma, mesothelioma, pleural fibrosis and pleural plaques indicating that both the lungs and the pleura are targets. The fibre pathogenicity paradigm was developed in the 1970s-80s and has a robust structure/toxicity relationship that enables the prediction of the pathogenicity of fibres depending on their length, thickness and biopersistence. Fibres that are sufficiently long and biopersistent and that deposit in the lungs can cause oxidative stress and inflammation. They may also translocate to the pleura where they can be retained depending on their length, and where they cause inflammation and oxidative stress in the pleural tissues. These pathobiological processes culminate in pathologic change - fibroplasia and neoplasia in the lungs and the pleura. There may also be direct genotoxic effects of fibres on epithelial cells and mesothelium, contributing to neoplasia. CNT show some of the properties of asbestos and other types of fibre in producing these types of effects and more research is needed. In terms of the molecular pathways involved in the interaction of long biopersistent fibres with target tissue the events leading to mesothelioma have been a particular area of interest. A variety of kinase pathways important in proliferation are activated by asbestos leading to pre-malignant states and investigations are under way to determine whether fibrous CNT also affects these molecular pathways. Current research suggests that fibrous CNT can elicit effects similar to asbestos but more research is needed to determine whether they, or other nanofibres, can cause fibrosis and cancer in the long term.