Investigation of the biodurability of wollastonite and xonotlite.

The in vivo durability of wollastonite materials, coated and uncoated, and of xonotlite was tested. Wollastonite is an anhydrous natural silicate and xonotlite is a hydrated synthetic calcium silicate. UICC crocidolite was used as a positive control with high durability. Using a dry-sizing technique, fractions from the stock materials were prepared according to the definition of "thoracic particulate mass" and "respirable particulate mass" of the American Conference of Governmental Industrial Hygienists. Fibers were instilled intratracheally into female Wistar rats, and the evenness of their distribution in the lung was checked by scanning electron microscopy (SEM). After serial sacrifices at 2 and 14 days, 1, 3, and 6 months, and low temperature ashing of the lung, the fibers were analyzed by SEM. The number and size distribution of fibers were investigated. The total number of crocidolite fibers decreased with a half-time of 240 days, but the number of fibers > 5 microns in length was unchanged after 6 months. The elimination kinetics of wollastonite fibers from the lung were relatively fast, with half-times of 15 to 21 days. The coating of wollastonite in Wollastocoat had no effect on this elimination process. For the thoracic fraction of wollastonite, the elimination from the lung was as fast as for the respirable particulate fraction. The elimination kinetics of xonotlite from the lung was very fast. This material consisted of single crystals of acicular morphology with a median length of 1.3 micron and of agglomerates of these crystals. More than 99% of single crystals and about 85 to 89% of the agglomerates were already eliminated 2 days after instillation

Significance of the biodurability of man-made vitreous fibers to risk assessment.

It is generally agreed that the biodurability of man-made vitreous fibers is a major factor for the characterization of potential health effects. As there is currently no standardization of experimental protocols to determine biodurabilty, the results of the clearance assays have not been used up to now for regulatory purposes. Methods used to analyze biodurability in animal models are short-term inhalational exposure and intratracheal instillation of rat respirable fibers. Both test methods have strengths and limitations for regulatory purposes. We outline recommended procedures for standardized biodurability assays that can be used to compare different fiber types. In animal experiments, biodurability is difficult to separate from biopersistence, as mucociliary and macrophage-mediated clearance occur simultaneously with dissolution and disintegration. For intratracheal instillation, a sized rat respirable sample must be used. Precautions should be taken to prevent aggregation of fibers in the lungs. Although from a scientific point of view questions remain about quantifying the influence of fiber length, diameter, dose, and exposure route, consistent data on the biodurability of vitreous glass fibers are available which may be used for regulatory purposes

Investigations on health-related properties of two sepiolite samples.

Published i.p. injection studies have shown different biological behavior of different sepiolite samples. There was no evidence for carcinogenic potential of sepiolite from Vicalvaro, Spain, whereas a high tumor incidence was reported for sepiolite from Finland. The low biological activity of the sepiolite from Vicalvaro, compared to the Finnish sample, could be caused by low in vivo persistence or by the short length of the fibers, or both. In this study a further sepiolite sample, obtained as a commercial sample originating from China, was investigated. This sample contained a higher fraction of fibers longer than 5 microns, comparable to the Finnish sepiolite sample. The fraction of fibers with a length > 5 microns was 0.12 and 2.2% for the Vicalvaro and Chinese sepiolite, respectively. For the fiber fraction longer than 8 microns, the corresponding values were 0.0045 and 0.82%. The in vivo persistence of the sepiolite samples from China and Vicalvaro was analyzed after intratracheal instillation of 2 mg in female Wistar rats. Fiber retention in the lungs was analyzed by transmission electron microscopy at different sacrifice dates up to 12 months after application. For the Vicalvaro sepiolite, a splitting of fiber bundles was found during retention time in the lung. Therefore, no half-time of the fiber clearance could be calculated from the number of fibers. The decrease of the calculated retained fiber mass was faster for the Vicalvaro sepiolite (T1/2 = 89 days) compared to the Chinese sepiolite (T1/2 = 129 days). For 2 or 3 rats per group, at sacrifice date 12 months after i.p. injection, the lung was investigated by histopathology. The main difference between both treatment groups was a more pronounced fibrotic response in the Chinese sepiolite-treated rats compared to those treated with Vicalvaro sepiolite. It is concluded that both the higher fraction of long sepiolite fibers and the slower elimination rate of the fiber mass in the Chinese sample were important factors for the different biological reaction in comparison with Vicalvaro sepiolite

Comparative investigations of the biodurability of mineral fibers in the rat lung.

The biodurability of various glass fibers, rockwool, and ceramic fibers was examined in rat lungs and compared with natural mineral fibers. Experiments were based on studies that have shown that the biodurability of fibers is one of the essential factors of the carcinogenic potency of these materials. Sized fractions of fibers were instilled intratracheally into Wistar rats. The evenness of distribution of fibers in the lung was checked by scanning electron microscopy (SEM) or careful examination of the fiber suspension before treatment. After serial sacrifices up to 24 months after treatment, the fibers were analyzed by SEM following low temperature ashing of the lungs. Parameters measured included number of fibers, diameter, and length distribution at the various sacrifice dates, so that analyses could be made of the elimination kinetics of fibers from the lung in relation to fiber length (FL). Size selective plots of the fiber elimination correlated with fiber diameters enables the mechanism of the fiber elimination (dissolution, fiber breakage, physical clearance) to be interpreted. The half-time of fiber elimination from the lung ranges from about 10 days for wollastonite to more than 300 days for crocidolite. The biodurability of man-made vitreous fibers (MMVF) is between these values and is dependent on the chemical composition of the fibers and the diameter and length distribution. Results indicate that the in vivo durability of glass fibers is considerably longer than expected from extrapolation of published data on their in vitro dissolution rates

Irreversible pulmonary changes induced in rat lung by dust overload.

The objective of this study was to investigate whether the effects of dust overload are reversible upon cessation of subchronic exposure to test toner. Female rats were exposed 6 hr/day, 5 days/week for 3 months to a test toner at 0, 10, and 40 mg/m3. The retained quantity of test toner in the lungs at the end of exposure was 0.4 and 3.0 mg for the low and high exposure groups, respectively. Fifteen months later, the corresponding values were 0.12 and 2.65 mg in the lungs. Alveolar clearance of tracer aerosols as well as cytologic and enzymatic parameters in the bronchoalveolar fluid was investigated at the end of exposure and subsequently up to 15 months later. The alveolar clearance of 59Fe2O3, 51Cr-polystyrene, and 85Sr-polystyrene tracer aerosols was slightly retarded at the low and substantially impaired at the high exposure level. At the low exposure level, there was some recovery in the clearance behavior up to 6 months after exposure. In contrast, at the high exposure level there was no indication of a reversal of the impaired clearance. For the beta-glucuronidase activity and the number of polymorphonuclear cells, the pattern of the effects was similar to the effects on the half-time tracer particle clearance. In conclusion, the dust overload at a lung burden of 3 mg test toner in rats was persistent for at least 15 months after termination of exposure

Significance of durability of mineral fibers for their toxicity and carcinogenic potency in the abdominal cavity of rats in comparison with the low sensitivity of inhalation studies.

At the same time that carcinogenicity of very thin glass fibers after intrapleural and intraperitoneal (ip) administration was demonstrated (1,2) researchers found that gypsum fibers and HCI-leached chrysotile fibers were easily soluble in the peritoneal cavity. This led to the conclusion that the chemical composition of fibers was not responsible for the carcinogenesis but that the degree of carcinogenic potency of a fiber depended on the extent to which it retained its fibrous structure. A thin glass fiber with a low biodurability did not induce tumors after ip injection of a high dose, although the ip test had been criticized for being "overly sensitive." The ip model has been the most successful for determining carcinogenicity of inorganic fibers and establishing dose-response relationships; but to determine the possibilities and limitations of this test model, very high doses of nonfibrous silicon carbide and of a slightly durable glass fiber type were injected ip in Wistar rats. No obviously acute or chronic toxic effect was observed in 90 weeks, but there was a 40% incidence of serosal tumors in the group treated with glass fibers. A pilot study on the persistence of slag fibers in the omentum of rats after ip injection showed a half-time of about 1 year. It was calculated that an ip injection of 10(9) fibers would lead to a concentration of fiber numbers in the ash of the omentum in the same range as the concentration in the lung after 2 years of inhalation exposure. The long-term inhalation study with fibers in rats has been called the "gold standard" for risk characterization.(ABSTRACT TRUNCATED AT 250 WORDS

Investigation on the durability of man-made vitreous fibers in rat lungs.

Two types of sized stonewool with median lengths of 6.7 and 10.1 microns and median diameters of 0.63 and 0.85 microns, and crocidolite with fibers of median length of 4.8 microns and median diameter of 0.18 microns were instilled intratracheally into female Wistar rats. A single dose of 2 mg in 0.3 ml saline was used for the stonewool samples and 0.1 mg in 0.3 ml saline for crocidolite. The evenness of distribution of fibers in the lung was checked by scanning electron microscopy (SEM). Five animals per group were sacrificed after 2 days, 1, 3, 6, and 12 months. After low-temperature ashing of the lungs about 200 fibers per animal were analyzed by SEM for length and diameter. The number and mass of fibers in the total lung were calculated. For the stonewool samples the decrease in the number of fibers in the lung ash followed approximately first order kinetics resulting in half-times of 90 and 120 days. The analysis of fiber number and diameter of different length fractions was used to estimate the contribution of three processes of fiber elimination: transport by macrophages for short fibers, breakage of fibers, and dissolution of fibers. (The process of transport by macrophages was found fastest for fibers with length < 2.5 microns). For the elimination of critical fibers with length > 5 microns, the breakage and dissolution were the most important processes. The breakage of fibers was predominant for one of the stonewool samples. The preferential type of the mechanism of fiber elimination is dependent on chemical composition and size distribution

Dose-response relationship of fibrous dusts in intraperitoneal studies.

The relationship between the number of fibers injected intraperitoneally and the occurrence of peritoneal mesotheliomas in rats was investigated using data from a series of carcinogenicity studies with several fibrous dusts. Based on observed tumor incidences ranging between 10 and 90%, the hypothesis of a common slope of dose-response relationships (parallel probit lines in probit analysis) cannot be rejected. In general, parallelism of probit lines is considered an indication of a common mode of action. Analysis of the shape of the dose-response relationship, with one apparent exception, shows virtually linear or superlinear behavior, i.e., from these data, there is no indication of a decrease in carcinogenic potency of an elementary carcinogenic unit at lower doses

Influence of the Wall Thicknesses on the Joint Quality During Magnetic Pulse Welding in Tube-to-Tube Configuration

The implementation of multi-material concepts, for example, in automotive engineering or aerospace technologies, requires adequate joining techniques. The Magnetic Pulse Welding (MPW) process allows for joining both similar and dissimilar materials without additional mechanical elements, chemical binders, or adverse influences of heat on the joining partners. In this process, an electro-conductive at (‘flyer’) part is accelerated by Lorentz forces and impacts the inner (‘parent’) part under high velocity and high pressure, leading to the formation of a metallurgical joint. Besides joining of sheets and tubes to solid cylinders, the connection of two tubes is of particular interest due to the increased lightweight potential. The present paper focuses on the MPW of aluminum (EN AW-6060) to steel (C45) tubes. An experimental study was performed, in which the wall thickness of the parent part was reduced successively. The deformation behavior of both the flyer and parent parts was recorded during the experiments by a two-probe Photon Doppler Velocimeter (PDV). The final shape of the joined specimens was analyzed by a 3D digitizer. An instrumented peel test was used for the determination of the weld quality. It was found that defect-free MPW of aluminum tubes on steel tubes without supporting mandrel is possible

Influence of the Free Compression Stage on Magnetic Pulse Welding of Tubes

In magnetic pulse welding (MPW) of tubular parts, the acceleration of the ‘flyer’ part typically corresponds to a free electromagnetic compression (EMC) process over the distance of the initial standoff between the outer and inner tube. During this process stage, already significant plastic strains occur. In addition, wrinkling is a phenomenon frequently observed during EMC. In this manuscript, influencing factors on the wrinkling effect are identified, taking the initial geometry of the flyer tube and its manufacturing process into account. Moreover, a link between the strains and wrinkles caused by the tube compression and the MPW process is made. An experimental study is performed aiming for the quantification of the plastic deformation during EMC. The effect of this deformation on the stability and adhesion of brittle surface layers is analyzed. Accompanying numerical simulations help to understand the wrinkle formation and its influencing factors. Based on the results, hints for an improved process design of MPW are given