Absence of carcinogenic response to multiwall carbon nanotubes in a 2-year bioassay in the peritoneal cavity of the rat.

Determinants of carbon nanotube toxicity

Part 2 summarises the results of a comparative LCA study of HT stone wool, flax representing crop grown products and paper wool representing recycled products applied for roof insulation, in which an attempt is made to answer the question of whether the biological products flax and paper wool are more environmentally preferable than the mineral product stone wool representing more traditional insulation materials. Of the three products compared, paper wool has, in general, the lowest global and regional environmental impacts and flax insulation the highest, with stone wool falling in between. A notable exception is the total energy use, where stone wool has the lowest consumption, followed by cellulose and flax. The study also addresses occupational health, using an approach similar to that used for risk assessment. Here, the modern less biopersistent stone wool products are seen as the safest alternatives, because of a low potential for exposure, sufficient animal testing and the absence of carcinogenic properties. Overall, the differences between the investigated products are of minor environmental significance compared to that achieved by their use, namely insulation of buildings, which saves energy corresponding to more than 100 times the environmental impacts incurred in their manufacture. The main conclusion is that the quality and fitness for use of an insulation product throughout its useful life span is the most important aspect in the life cycle of insulation materials.

A Comparative Life Cycle Assessment of Building Insulation Products made of Stone Wool, Paper Wool and Flax Part 1: Background, Goal and Scope, Life Cycle Inventory, Impact Assessment and Interpretation

A theoretical approach to the deposition and clearance of fibers with variable size in the human respiratory tract.

With the initial understanding of the relationship of asbestos to disease, little information was available on whether the two different groups of minerals which are called asbestos were of similar or different potency in causing disease. Asbestos was often described as a durable fiber which if inhaled would remain in the lung and cause disease. It has been only more recently with the development of a standardised protocol for evaluating the biopersistence of mineral fibers in the lung that the clearance kinetics of the serpentine chrysotile have been shown to be dramatically different from those of amphibole asbestos with chrysotile clearing rapidly from the lung. In addition, recent epidemiology studies also differentiate chrysotile form amphibole asbestos. The above mentioned biopersistence studies have indicated that chrysotile from Canada and California clear rapidly from the lung once inhaled. However, variations in chrysotile mineralogy have been reported depending upon the region. This is most likely associated with variations in the forces which created the chrysotile fibers centuries ago. In the present study, the dynamics and rate of clearance of chrysotile from the Cana Brava mine in central Brazil was evaluated in a comparable inhalation biopersistence study in the rat. For synthetic vitreous fibers, the biopersistence of the fibers longer than 20 µm has been found to be directly related to their potential to cause disease. This study was designed to determine lung clearance (biopersistence) and translocation and distribution within the lung. As the long fibers have been shown to have the greatest potential for pathogenicity, the chrysotile samples were specifically chosen to have more than 450 fibers/cm 3 longer than 20 µm in length present in the exposure aerosol.

The Biopersistence of Brazilian Chrysotile Asbestos Following Inhalation

A summary is given of the pathology results after intraperitoneal (i.p.) injection in rats of insulation wool HT, representing the new biosoluble types. The pathology results are compared with a previously conducted i.p. study with traditional stone wool D6 (with similar chemical composition to MMVF21). The HT fibre is characterized by a relatively high content of aluminium and a relatively low content of silica compared to MMVF21. HT has a high in vitro dissolution rate at pH 4.5, a relatively low dissolution rate at pH 7.5 and is less biopersistent than the MMVF21 fibre. Female Wistar rats received a dose of 2 x 10(9) WHO HT fibres by i.p. injection. The fibres had been size-selected to be largely rat respirable. The negative control group was exposed to saline. Following exposure, the animals were maintained until survival in one group fell below 20%. At this time, all animals were killed. All animals were subjected to a necropsy examination; any gross abnormalities observed at necropsy were subjected to histopathological examination. In addition, histopathology was carried out on a predefined list of tissues. The incidences of lesions and survival in the control and fibre dosed animals were compared using appropriate statistical methods to determine whether the dosed animals showed adverse effects on survival or a positive carcinogenic response. The main protocol for the previously conducted study with D6 (MMVF21) was similar, but the animals were maintained as long as they survived, and the WHO fibre dose was lower. The results of the comparative study showed a marked difference in the i.p. pathogenicity of D6 (MMVF21) and HT in terms of their carcinogenic potential. D6 (MMVF21) caused a statistically significant increase of mesotheliomas in the peritoneal cavity compared to the negative control, but the HT fibre did not cause any mesotheliomas or any increase in other tumour types.

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C. G. Collier

Papers

Carcinogenicity studies after intraperitoneal injection of two types of stone wool fibres in rats.