Use of short-term assays to evaluate the potential toxicity of two new biosoluble glasswool fibers

Critical Choices in Predicting Stone Wool Biodurability: Lysosomal Fluid Compositions and Binder Effects

The hazard potential, including carcinogenicity, of inhaled man-made vitreous fibers (MMVFs) is correlated with their biodurability in the lung, as prerequisite for biopersistence. Abiotic dissolution testing serves to predict biodurability. We re-analyzed the International Agency for Research on Cancer Monograph on MMVFs and found that the correlation between in vivo biopersistence and abiotic dissolution presented therein confounded different simulant fluids and further confounded evaluation of leaching vs structural elements. These are critical choices for abiotic dissolution testing, as are binder removal and the rate of the flow that removes ions during testing. Therefore, we experimentally demonstrated how fluid composition and binder affect abiotic dissolution of a representative stone wool MMVF. We compared six simulant fluids (all pH 4.5, reflecting the environment of alveolar macrophage lysosomes) that differed in organic acids, which have a critical role in their ability to modulate the formation of Si-rich gels on the fiber surfaces. Removing the binder accelerates the average dissolution rate by +104% (max. + 273%) across the fluids by suppression of gel formation. Apart from the high-citrate fluid that predicted a 10-fold faster dissolution than is observed in vivo, none of the five other fluids resulted in dissolution rates above 400 ng/cm²/h, the limit associated with the exoneration from classification for carcinogenicity in the literature. These findings were confirmed with and without binder. For corroboration, five more stone wool MMVFs were assessed with and without binder in one specific fluid. Again, the presence of the binder caused gel formation and reduced dissolution rates. To enhance the reliability and robustness of abiotic predictions of biodurability, we recommend replacing the critically influential citric acid in pH 4.5 fluids with other organic acids. Also, future studies should consider structural transformations of the fibers, including changes in fiber length, fiber composition, and reprecipitation of gel layers.

Occupational safety and health, green chemistry, and sustainability: a review of areas of convergence

With increasing numbers and quantities of chemicals in commerce and use, scientific attention continues to focus on the environmental and public health consequences of chemical production processes and exposures. Concerns about environmental stewardship have been gaining broader traction through emphases on sustainability and "green chemistry" principles. Occupational safety and health has not been fully promoted as a component of environmental sustainability. However, there is a natural convergence of green chemistry/sustainability and occupational safety and health efforts. Addressing both together can have a synergistic effect. Failure to promote this convergence could lead to increasing worker hazards and lack of support for sustainability efforts. The National Institute for Occupational Safety and Health has made a concerted effort involving multiple stakeholders to anticipate and identify potential hazards associated with sustainable practices and green jobs for workers. Examples of potential hazards are presented in case studies with suggested solutions such as implementing the hierarchy of controls and prevention through design principles in green chemistry and green building practices. Practical considerations and strategies for green chemistry, and environmental stewardship could benefit from the incorporation of occupational safety and health concepts which in turn protect affected workers.

Macrophage culture as a suitable paradigm for evaluation of synthetic vitreous fibers

The ultimate goal of toxicologic investigation of synthetic vitreous fibers (SVFs) is to provide essential input for the assessment of human risk to their exposure. Toxicity of mineral fibers is usually evaluated by testing biopersistence in rodent model. However, a cellular model would be much appreciated in order to reduce, refine, and replace animal models. Pulmonary disorders triggered by inhalation of occupational or environmental mineral particulates can be the endpoints of a chronic inflammatory process in which alveolar macrophages (AMs) play a crucial role. Depending on the type of SVF involved, phagocytosis of fiber leads to activation of macrophages, resulting in release of fiber components and potent mediators, such as reactive oxygen or nitrogen species and cytokines. As a matter of fact, macrophages should be the cells of choice since SVF toxicity is the consequence of fibers and alveolar macrophages interaction. Today, monocytes and macrophages culture are firmly established as a paradigm in toxicology when several endpoints are assayed in macrophages: (1) fiber durability, (2) fiber surface changes, (3) oxidative stress and genotoxicity in macrophage, and (4) macrophage cell viability and apoptosis. This article is a review of up-to-date knowledge of in vitro studies involving macrophages, and assesses endpoints of macrophage toxicity with an emphasis on (1) dissolution, (2) scanning electron microscopy analysis, (3) cytotoxicity, and (4) gene expression.

Effects of various man-made mineral fibers on cell apoptosis and viability

Evaluating the pathogenic potentials of man-made mineral fibers (MMMF) is an important task performed by the European Community. Noting that it has been proposed that the use of laboratory animals for scientific tests should be reduced or phased out, macrophages then become the cells of choice for conducting in vitro studies. We have evaluated the in vitro toxicity of six commercial stonewool fibers (A, B1, B2, C, D, and E) on U-937 cells. The physical interaction between U-937 cells and MMMF was observed using scanning electron microscopy, and the cytotoxicity was evaluated by studying cell viability using MTT assay and cell apoptosis with an ELISA detection kit. Scanning electron microscopy (SEM) analysis has shown that long fibers can be covered by several macrophages, and that a small fiber can be completely engulfed by one cell. With 50 microg/mL of MMMF, a decrease in cell viability appeared after seven days of incubation, whereas 200 microg/mL induced loss of viability and apoptosis after one day. Fiber D, comprising a high proportion of fibers >20 microm in length and a high concentration of MgO, induced the highest loss in viability and the highest rate of apoptosis compared to the other five fibers. Whether this toxic effect is related to either the physical characteristics of the fibers (such as length), or to the high concentration of magnesium is still to be determined. Because the results can be rapidly obtained, the proposed model is suitable for studying the toxicities of mineral components, even if the tested concentrations are far from the ones reached in the lung.

Indices of fiber biopersistence and carcinogen classification for synthetic vitreous fibers (SVFs)

It is generally accepted that the biopersistence of a synthetic vitreous fiber (SVF) is an important determinant of its biological activity. Experimental protocols have been developed to measure the biopersistence of an SVF from short-term inhalation experiments with rats. Clearance kinetics of long (>20 microm) fibers (those believed to have greatest biological activity) have been approximated by one- or two-pool models. Several measures or indices of biopersistence have been proposed in the literature of which three, the weighted half-time (WT(1/2)), the time required to clear 90% of long fibers (T(0.9)), and the so-called slow-phase half-time (T(2)), have been investigated in some detail. This paper considers both one- and two-pool models for long fiber clearance, characterizes the properties of these candidate indices of fiber biopersistence, identifies measures with potentially superior statistical properties, suggests possible cutoff values based on the relation between biopersistence and the outcome of chronic bioassays, and offers comments on the selection of efficient experimental designs. This analysis concludes that WT(1/2) and T(0.9) are highly correlated, are efficient predictors of the outcome of chronic bioassays, and have reasonable statistical properties. T(2), although perhaps attractive in principle, suffers from some statistical shortcomings when estimated using present experimental protocols. The WT(1/2) is shown to be directly proportional to the cumulative exposure (fiber days) after the cessation of exposure and also the mean residence time of these fibers in the lung.