Effects of rock wool on the lungs evaluated by magnetometry and biopersistence test

Our plain-English summary of Effects of rock wool on the lungs evaluated by magnetometry and biopersistence test, by Y. Kudo, M. Kotani, M. Tomita, et al (Journal of Occupational Medicine and Toxicology, 2009).

The study

• Authors: Y. Kudo, M. Kotani, M. Tomita, Y. Aizawa
• Journal: Journal of Occupational Medicine and Toxicology
• Published: 2009;4:5
• Cited by: 3 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Background: Asbestos has been reported to cause pulmonary fibrosis, and its use has been banned all over the world. The related industries are facing an urgent need to develop a safer fibrous substance. Rock wool (RW), a kind of asbestos substitute, is widely used in the construction industry. In order to evaluate the safety of RW, we performed a nose-only inhalation exposure study in rats. After one-month observation period, the potential of RW fibers to cause pulmonary toxicity was evaluated based on lung magnetometry findings, pulmonary biopersistence, and pneumopathology.

Methods: Using the nose-only inhalation exposure system, 6 male Fischer 344 rats (6 to 10 weeks old) were exposed to RW fibers at a target fiber concentration of 100 fibers/cm3 (length [L] > 20 mum) for 6 hours daily, for 5 consecutive days. As a magnetometric indicator, 3 mg of triiron tetraoxide suspended in 0.2 mL of physiological saline was intratracheally administered after RW exposure to these rats and 6 unexposed rats (controls). During one second magnetization in 50 mT external magnetic field, all magnetic particles were aligned, and immediately afterwards the strength of their remanent magnetic field in the rat lungs was measured in both groups. Magnetization and measurement of the decay (relaxation) of this remanent magnetic field was performed over 40 minutes on 1, 3, 14, and 28 days after RW exposure, and reflected cytoskeleton dependent intracellular transport within macrophages in the lung. Similarly, 24 and 12 male Fisher 344-rats were used for biopersistence test and pathologic evaluation, respectively.

Results: In the lung magnetometric evaluation, biopersistence test and pathological evaluation, the arithmetic mean value of the total fiber concentration was 650.2, 344.7 and 390.7 fibers/cm3, respectively, and 156.6, 93.1 and 95.0 fibers/cm3 for fibers with L > 20 mum, respectively. The lung magnetometric evaluation revealed that impaired relaxation indicating cytoskeletal toxicity did not occur in the RW exposure group. In addition, clearance of the magnetic tracer particles was not significantly affected by the RW exposure. No effects on lung pathology were noted after RW exposure.

Conclusion: These findings indicate that RW exposure is unlikely to cause pulmonary toxicity within four weeks period. Lung magnetometry studies involving long-term exposure and observation will be necessary to ensure the safety of RW.

In plain English

This was an animal experiment from Japan on rock wool, a man-made fiber used as an asbestos substitute in construction. Male Fischer 344 rats breathed rock wool fibers through their noses for 6 hours a day on 5 consecutive days. To test the lung's defense cells (macrophages), magnetic iron oxide particles were placed in the lungs of 6 exposed rats and 6 unexposed control rats. Their magnetic signal was tracked 1, 3, 14 and 28 days after exposure. Separate rats were used to count fibers left in the lungs and to examine lung tissue. The magnetic measurements showed no significant differences between exposed and control rats on any day, although the authors wrote that particle clearance in exposed rats was impaired "in tendency." Fiber numbers in the lungs fell significantly by day 28 compared with day 1. Calculated half-lives were 35 days for all fibers and 16 days for fibers longer than 20 micrometers. No pulmonary fibrosis was seen. The authors concluded that rock wool exposure may not cause significant lung toxicity within four weeks, and that evaluation for at least one year is needed.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Animal experiment: nose-only inhalation exposure of rats, evaluated by lung magnetometry, a biopersistence test (fiber counts and sizes in the lungs over time) and pathological examination
• Who was studied: Male Fischer 344 rats, 6 to 10 weeks old, at Kitasato University School of Medicine, Japan. Magnetometry used 6 rock-wool-exposed and 6 unexposed control rats. The biopersistence test used 12 rats per experiment, repeated twice (24 rats). Pathological evaluation used 12 rats.
• Exposure: Rock wool fibers (geometric mean length 15.49 µm, width 2.44 µm; composed of SiO2 39%, CaO 33%, Al2O3 14% and smaller amounts of other oxides), inhaled through the nose for 6 hours daily for 5 consecutive days. Rats in the magnetometry part also received 3 mg of triiron tetraoxide particles into the trachea one day after exposure.
• Main results:
  • Measured chamber concentrations in the magnetometry experiment averaged 650.2 (SD 367.3) fibers/cm3 for all fibers and 156.6 (SD 104.7) fibers/cm3 for fibers longer than 20 µm. In the biopersistence test they averaged 344.7 and 93.1 fibers/cm3, and in the pathological evaluation 390.7 and 95.0 fibers/cm3.
  • Decay (relaxation) of the magnetic field, which reflects macrophage function, did not differ significantly between rock-wool-exposed and control rats on any measurement day.
  • Both groups cleared the magnetic particles rapidly. In the rock-wool-exposed group, clearance was described as impaired in tendency. The discussion reports no significant differences between the groups.
  • In the biopersistence test, fiber numbers in every size category were significantly lower 28 days after exposure than 1 day after exposure (p less than 0.05).
  • Calculated half-lives of rock wool fibers in rat lungs were 35 days for all fibers, 16 days for fibers longer than 20 µm, and 35 days for WHO fibers.
  • Fiber width in the lungs was significantly smaller at day 3 and day 28 than at day 1 (p less than 0.05).
  • On pathological examination, lung tissue showed no pulmonary fibrosis and was almost normal. These data were not shown in the article.
• The authors' conclusion: The authors concluded that rock wool exposure may not cause significant lung toxicity within a four-week period.
• Limitations the authors state:
  • Observation lasted four weeks. The authors stated that lung toxicity should be evaluated for at least one year after exposure, which they said they were doing in an ongoing study.

Topics

Medical terms in this study, explained in our Lexicon: biopersistence, Pulmonary Fibrosis, Macrophage, Pathology.

Related studies

• Biopersistence of rock wool in lungs after short-term inhalation in rats — Y. Kudo, Y. Aizawa (2008)
• Comparative cytotoxicity study of rock wool and chrysotile by cell magnetometric evaluation — Y. Kudo, M. Watanabe, et al. (2003)
• Cytotoxicity study of rock wool by cell magnetometric evaluation — Y. Kudo, M. Kotani, et al. (2009)
• Behavior of new type of rock wool (HT wool) in lungs after exposure by nasal inhalation in rats — Y. Kudo, K. Shibata, et al. (2005)
• Evaluation of hazardousness of refractory fibers by cell magnetometry — Y. Kudo, M. Kotani, et al. (2010)
• Mechanism of refractory ceramic fiber- and rock wool-induced cytotoxicity in alveolar macrophages — K.A. Kim, W.K. Lee, et al. (2001)

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