Quantitative assessment of chrysotile fibrils in the bloodstream of rats which have ingested the mineral under different dietary conditions

Asbestiform Amphiboles and Cleavage Fragments Analogues: Overview of Critical Dimensions, Aspect Ratios, Exposure and Health Effects

The term asbestos refers to a group of serpentine (chrysotile) and amphibole (amosite, crocidolite, anthophyllite, tremolite and actinolite) minerals with a fibrous habit. Their chemical-physical properties make them one of the most important inorganic materials for industrial purposes and technological applications. However, the extraction, use and marketing of these minerals have been prohibited due to proven harmful effects, mainly involving the respiratory system. In addition to the known six minerals classified as asbestos, the natural amphiboles and serpentine polymorphs antigorite and lizardite, despite having the same composition of asbestos, do not have the same morphology. These minerals develop chemical and geometric (length > 5 μm, width < 3 μm and length: diameter > 3:1), but not morphological, analogies with asbestos, which is regulated by the WHO. The debate about their potential hazardous properties is open and ongoing; therefore, their morphological characterization has a key role in establishing a reliable asbestos hazard scenario. This review focuses on evaluating the most relevant papers, evidencing the need for a reappraisal. Different in vitro, in vivo and epidemiological studies report information about cleavage fragments with critical dimensions similar to asbestos fibres, but very few works target fragments below 5 µm in length. Breathable smaller fibres could have deleterious effects on human health and cannot be disregarded from the risk assessment process. Furthermore, a few studies suggest that the carcinogenic nature of short fibres is not excluded. This review highlights that it is worth investigating the effects of this size range of elongated mineral particles and fibres.

Nonpulmonary outcomes of asbestos exposure

The adverse pulmonary effects of asbestos are well accepted in scientific circles. However, the extrapulmonary consequences of asbestos exposure are not as clearly defined. In this review the potential for asbestos to produce diseases of the peritoneum, immune, gastrointestinal (GIT), and reproductive systems are explored as evidenced in published, peer-reviewed literature. Several hundred epidemiological, in vivo, and in vitro publications analyzing the extrapulmonary effects of asbestos were used as sources to arrive at the conclusions and to establish areas needing further study. In order to be considered, each study had to monitor extrapulmonary outcomes following exposure to asbestos. The literature supports a strong association between asbestos exposure and peritoneal neoplasms. Correlations between asbestos exposure and immune-related disease are less conclusive; nevertheless, it was concluded from the combined autoimmune studies that there is a possibility for a higher-than-expected risk of systemic autoimmune disease among asbestos-exposed populations. In general, the GIT effects of asbestos exposure appear to be minimal, with the most likely outcome being development of stomach cancer. However, IARC recently concluded the evidence to support asbestos-induced stomach cancer to be "limited." The strongest evidence for reproductive disease due to asbestos is in regard to ovarian cancer. Unfortunately, effects on fertility and the developing fetus are under-studied. The possibility of other asbestos-induced health effects does exist. These include brain-related tumors, blood disorders due to the mutagenic and hemolytic properties of asbestos, and peritoneal fibrosis. It is clear from the literature that the adverse properties of asbestos are not confined to the pulmonary system.

Generation and characterization of test atmospheres with nanomaterials

To ensure the product safety of nanomaterials, BASF has initiated an extensive program to study the potential inhalation toxicity of nanosize particles. As preparation work for upcoming inhalation studies, the following manufactured nanomaterials have been evaluated for their behavior in an exposure system designed for inhalation toxicity studies: titanium dioxide, carbon black, Aerosil R104, Aerosil R106, aluminum oxide, copper(II) oxide, amorphous silicon dioxide, zinc oxide, and zirconium(IV) oxide. As the physicochemical properties and the complex nature of ultrafine aerosols may substantially influence the toxic potential, the particle size, specific surface area, zeta potential, and morphology of each of the materials were determined. Aerosols of each material were generated using a dry powder aerosol generator and by nebulization of particle suspensions. The mass concentration of the particles in the inhalation atmosphere was determined gravimetrically and the particle size was determined using a cascade impactor, an optical particle counter, and a scanning mobility particle sizer. The dispersion techniques used generated fine aerosols with particle size distributions in the respiratory range. However, as a result of the significant agglomeration of nanoparticles in the test materials evaluated, no more than a few mass percent of the materials were present as single nanoparticles (i.e., < 100 nm). Considering the number, a greater percentage of nanoparticles was present. Based on the obtained results and experience with the equipment, a technical setup for inhalation studies with nanomaterials is proposed. Furthermore, a stepwise testing approach is recommended that also could reduce the number of animals used in testing.

Carbon nanotubes: a review of their properties in relation to pulmonary toxicology and workplace safety

Carbon nanotubes (CNT) are an important new class of technological materials that have numerous novel and useful properties. The forecast increase in manufacture makes it likely that increasing human exposure will occur, and as a result, CNT are beginning to come under toxicological scrutiny. This review seeks to set out the toxicological paradigms applicable to the toxicity of inhaled CNT, building on the toxicological database on nanoparticles (NP) and fibers. Relevant workplace regulation regarding exposure is also considered in the light of our knowledge of CNT. CNT could have features of both NP and conventional fibers, and so the current paradigm for fiber toxicology, which is based on mineral fibers and synthetic vitreous fibers, is discussed. The NP toxicology paradigm is also discussed in relation to CNT. The available peer-reviewed literature suggests that CNT may have unusual toxicity properties. In particular, CNT seem to have a special ability to stimulate mesenchymal cell growth and to cause granuloma formation and fibrogenesis. In several studies, CNT have more adverse effects than the same mass of NP carbon and quartz, the latter a commonly used benchmark of particle toxicity. There is, however, no definitive inhalation study available that would avoid the potential for artifactual effects due to large mats and aggregates forming during instillation exposure procedures. Studies also show that CNT may exhibit some of their effects through oxidative stress and inflammation. CNT represent a group of particles that are growing in production and use, and therefore, research into their toxicology and safe use is warranted.

Asbestos: toxicology and risk assessment for the general population in The Netherlands

Within the scope of the preparation of Integrated Criteria Documents for priority compounds in The Netherlands, the possible health effects of oral and inhalatory exposure to asbestos for the general population were evaluated. It was concluded from the results of experiments in animals that exposure to asbestos by the oral route is not carcinogenic and is not expected to present a health risk to the general population. Inhaled asbestos, however, is distinctly carcinogenic to man, giving rise to lung tumours, and mesotheliomas of the pleura and peritoneum. Chrysotile asbestos appears to be less potent in inducing mesotheliomas than the amphiboles, but all types of asbestos appear to have a similar potency for inducing lung cancer. The risk of mesothelioma is not expected to be influenced by smoking, whereas the risk of lung cancer is expected to be ten times higher in smokers than in non-smokers exposed to the same asbestos concentrations. Risk-assessment models for the inhalatory route, for the general population, are based on linear non-threshold extrapolation of occupational exposure to much lower environmental concentrations. These models give only a rough approximation of the risk of environmental exposure to asbestos. In accordance with the Air Quality Guidelines of the World Health Organization (World Health Organization, 1987), it was estimated that an extra risk of lung cancer of one in 10(6) (in the general population, with 30% smokers) may be presented by lifetime exposure to asbestos fibres longer than 5 microns, measured by electron microscopy, at concentrations of 100-1000/m3. It was further estimated that an extra risk of mesothelioma of one in 10(6) may be presented by lifetime exposure to 10-100 amphibole fibres/m3 or to a range of 100-10000 chrysotile fibres/m3 (fibres longer than 5 microns). From the current asbestos concentrations, the risk of mesothelioma for the general population in The Netherlands appears to be negligible; the extra risk of lung cancer is expected to be higher than 1 in 10(6) near asbestos sources, whereas it appears to be negligible in background areas and in most large cities and industrial areas. However, it must be borne in mind that the validity of the risk figures given is difficult to judge.

Pleural migration of chrysotile fibers after intratracheal injection in rats

After intratracheal injection of 0.5 mg of UICC chrysotile, rats were sacrificed at various time intervals over a 1-month period, and their pleural cavity washed with saline. Samples were examined by means of transmission electron microscopy for identification, quantitation, and sizing of chrysotile fibers. No fibers were found in control rats injected with saline. The size and quantity of fibers that reached the pleural cavity of test rats was time-dependent, with two peaks on day 7 (mean number = 9.6 X 10(4); mean length = 1.3 micron) and on day 21 (mean number = 1.3 X 10(5); mean length = 0.3 micron). Such variations are compatible with a heterogeneous migration of chrysotile fibrils toward the pleura.