After scouring the internet and acoustic forums for information, I found conflicting conclusions on the safety of rock wool. I decided to do my own digging.

A report published on March 27, 2009, Effects of rock wool on the lungs evaluated by magnetometry and biopersistence test, found that there were no effects on lung pathology in male Fischer 344 rats (6 to 10 weeks old) exposed to rock wool fibers for 6 hours a day for 5 consecutive days. The half life of all the fibers was 35 days, 15 days for fibers with a length of over 20 µm and 35 days for WHO fibers – which have a length greater than µm and a width shorter than 3 µm.

A similar study published on May 26, 2009, Behavior of rock wool in lungs after exposure by nasal inhalation in rats, where male Fischer 344 rats (6–10 weeks old) were exposed to rock wool fibers for 3 hours daily for five consecutive days through nose only inhalation, found the half life of fibers to be 32 days for total fiber number, 86 days for fiber 5 µm or less, 31 days for fibers 20 µm or less, 10 days for fibers over 20 µm, and 27 days for WHO fibers. The study suggested that rock wool fibers are safe, however, it was stated that it is difficult to give a definitive answer on such a short term study.

A long term study published in Feb 1982, Mortality patterns of rock and slag mineral wool production workers: an epidemiological and environmental study, concluded that all repairable fibers should be viewed with caution. The study found increased number of deaths due to cancer of the digestive system and non-malignant respiratory disease in workers who had exposure to mineral fibers for 20 years or more. It is also reported that five mesotheliomas were produced in rats through the injection of both coated and uncoated rock wool fibers with diameters ranging from 0.2 to 3 µm. Out of the 596 study members, 188 deaths occurred, 4 were war deaths and so were ruled out of the study. None of the cause-specific excesses were statistically significant, but the number of deaths due to cancer of the digestive system and non-malignant respiratory disease, excluding influenza and pneumonia, were increased. Five office workers also died, 3 of which had worked in mineral wool production for over 5 years, of cancer of the digestive system. The study had an expectation of 165.6 deaths over the time period, but only 149 occurred, however the number of deaths from cancer of the digestive system and non-malignant respiratory disease was slightly increased. The excess of non-malignant respiratory disease seemed to be more evident after 20 years since first exposure. It was concluded that none of the results were statistically significant. Other factors such as diet and ethnicity could not be ruled out, since they are implicated to be factors in cancers of the digestive system, however, the low country death rate for cancer of the digestive system would argue against local diet or other indigenous factors being responsible for the excess of cancers. Smoking patterns were also not assessed, and could have contributed to the excess in non-malignant respiratory disease, but since no excess deaths from lung cancer occurred, it is unlikely to be a significant factor. Due to the consistency of the study, further investigation will be needed to rule out carcinogenicity and non-malignant respiratory disease caused by rock wool fibers.

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“The cytotoxicity of rock wool (RW), an asbestos substitute, was evaluated by cell magnetometry. Alveolar macrophages were isolated from male Fisher rats. Following addition of triiron tetraoxide (Fe3O4) to macrophages, RW was added. Then, the remnant magnetic field strength was measured for 20 min after magnetization by an external field. Relaxation, an indicator of decay of cytotoxicity, was observed by cell magnetometry immediately postmagnetization in the group to which RW was added. In general, materials phagocytosed by macrophages are ingested into phagosomes and digested while migrating. This migration of phagosomes occurs by polymerization and depolymerization of the cytoskeleton. As a result of evaluation, relaxation was not delayed by addition of RW, since RW caused no effect on the cytoskeleton. It was suggested that RW has no cytotoxicity as evaluated by cell magnetometry.”

“The fiber glass (FG) and rock/slag wool (RSW) manufacturers have developed a Health and Safety Partnership Program (HSPP) with the participation and oversight of the Occupational Safety and Health Administration (OSHA). Among its many provisions the HSPP includes the continuing study of FG and RSW workplace concentrations in manufacturing facilities operated by FG/RSW producers and among their customers and end users. This analysis estimates the probable cumulative lifetime exposure (fiber-months/cubic centimeter [f-months/cc]) to those who install FG and RSW insulation in residential, commercial, and industrial buildings in Canada and the United States. Both professional and do-it-yourself (DIY) cohorts are studied and the estimated working lifetime exposures are compared with benchmark values derived from an analysis of the epidemiological studies of FG and RSW manufacturing cohorts. The key finding of this analysis is that both of these end-user cohorts are likely to have substantially lower cumulative lifetime exposures than the manufacturing cohorts. As the most recent updates of the epidemiological studies concluded that there was no significant increase in respiratory system cancer among the manufacturing cohorts, there is likely to be even less risk for the installer cohorts. This analysis also underscores the wisdom of stewardship activities in the HSPP, particularly those directed at measuring and controlling exposure.”

“In assessing the health evidence concerning man-made mineral fibers, the chemical composition, surface activity, durability, and size of fibers have to be taken into account. Special-purpose fine glass fibers need to be separated from the insulation wools (glass, rock, and slag wool). The epidemiological evidence is sufficient to conclude that there has been no mesothelioma risk to workers producing or using glass wool, rock wool, or slag wool. The epidemiological studies have been large and powerful, and they show no evidence of a cause-effect relationship between lung cancer and exposure to glass wool, rock wool, or slag wool fibers. There is some evidence of a small cancer hazard attached to the manufacturing process in slag wool plants 20 to 50 years ago, when asbestos was used in some products and other carcinogenic substances were present. However, this hazard is not associated with any index of exposure to slag wool itself. Animal inhalation studies of ordinary insulation wools also show that there is no evidence of hazard associated with exposure to these relatively coarse, soluble fibers. The evidence of carcinogenicity is limited to experiments with special-purpose fine durable glass fibers or experimental fibers, and only when these fibers are injected directly into the pleural or peritoneal cavity. Multiple chronic inhalation studies of these same special-purpose fine glass fibers have not produced evidence of carcinogenicity. It is suggested that the present IARC evaluation of the carcinogenic risk of insulation wools should be revised to Category 3: not classifiable as to carcinogenicity to humans.”

“Since 2001, three new community-based, case-control studies, two detailed analyses of existing cohort studies and two reviews/meta-analyses were published. These studies revealed no consistent evidence of an increased respiratory system cancer risk in relation to glass wool exposure.”

“In this study, we analyzed the effects of synthetic vitreous fibers (SVFs) on a mesothelial (MeT5A) and a fibroblast cell line (NIH3T3), compared to those exerted by crocidolite asbestos fibers. SVFs (glass wool, rock wools) do not induce significant changes in cell mortality, whereas crocidolite asbestos fibers caused a dose-dependent cytotoxicity.We investigated the correlation between the fiber-induced cytotoxicity and the extent and type of interaction of the fibers with the cell surface, and we observed that SVFs, unlike crocidolite asbestos fibers, establish few and weak interactions. Moreover, after internalization, crocidolite asbestos fibers are often found free in the cytoplasm, whereas glass wool fibers are mainly localized inside cytoplasmic vacuoles. After treatments, we also detected signs of oxidative stress, revealed by an increased reactive oxygen species (ROS) production and by an induction of superoxide dismutase (SOD) activity. The lipoperoxidative damage was characterized by a decrease in polyunsaturated fatty acids (PUFA), an increase in the content of thiobarbituric reactive species (TBARS) and a consumption of vitamin E, as a lipophilic antioxidant.

Furthermore, we investigated the effect of fiber exposure on cell proliferation. and it was found that, unlike crocidolite asbestos fibers, SVFs did not induce a significant increase in DNA synthesis.”

“The introduction of man-made vitreous fibers (MMVFs) as a substitute for asbestos in industrial and residential applications raises concerns about their potential health hazards. The aim of our study was to assess cytotoxic and oxidative effects induced on a human mesothelial cell line (MeT-5A) by exposure to glass wool (GW), rock wool (RW) and refractory ceramic fibers (RCF) in comparison with crocidolite asbestos (CR). MeT-5A cells were exposed for 24 h to 2, 5 and 10 μg/cm2 of MMVF and crocidolite fibers and analysed by scanning electron microscope (SEM) for cell surface alterations. Cells were exposed for 2 h to 1, 2, 5 and 10 μg/cm2 of the same fibers and analysed by enzyme Fpg-modified comet test for direct and oxidative DNA damage. SEM revealed loss of microvilli in cells exposed to RCF and numerous blebs in cells exposed to higher doses of RW. Comet test showed significant direct DNA damage in cells exposed to RCF even at the lowest dose. Comet test with Fpg, that permits the detection of oxided DNA bases, showed significant oxidative DNA damage in cells exposed to higher doses of RW. The presence of DNA damage and alterations of cell surface induced by low doses of RCF and the presence of oxidative DNA damage and blebs on cell surface in cells exposed to higher dose of RW suggest possible cytotoxic, oxidative and genotoxic effects for these MMVFs.”



“Inhalation studies were conducted to determine the chronic biological effects in rodents of respirable fractions of different man-made vitreous fibres (MMVFs), including refractory ceramic fibre (RCF), fibrous glass, rock (stone) wool and slag wool. Animals were exposed nose-only, 6 h per day, 5 days per week, for 18 months (hamsters) or 24 months (rats). Exposure to 10 mg m−3 of crocidolite or chrysotile asbestos induced pulmonary fibrosis, lung tumours and mesothelioma in rats, thus validating the inhalation model with known human carcinogenic fibres. Exposure of rats to 30 mg m−3 of refractory ceramic fibres (RCF) also resulted in pulmonary fibrosis as well as significant increases in lung tumours and mesothelioma. In hamsters, 30 mg m−3 of RCF induced a 41% incidence of mesotheliomas. Exposure of rats to 30 mg m−3 of fibre glasses (MMVF 10 or 11) or of slag wool (MMVF 22) was associated with an inflammatory response, but no mesotheliomas or significant increase in the lung tumours were observed. Rock wool (stone wool: MMVF 21) at the same exposure level resulted in minimal lung fibrosis, but no mesotheliomas or significant increase in the lung tumours were observed. Fibre numbers (WHO fibres) and dimensions in the aerosols and lungs of exposed animals were comparable in this series of inhalation studies. Differences in lung fibre burdens and lung clearance rates could not explain the differences observed in the toxicologic effects of the MMVFs. These findings indicate that dose, dimension and durability may not be the only determinants of fibre toxicity. Chemical composition and the surface physico-chemical properties of the fibres may also play an important role.”

“Five inhalation studies of synthetic vitreous fibres have recently investigated experimental tumorigenic responses to four different refractory ceramic fibres (RCF), two fibre glasses, one stone (rock) wool and one slag wool. Except for one RCF, the source materials were typical commercial products. Three studies included positive control groups exposed to chrysotile or crocidolite asbestos. The studies were conducted using state-of-the-art technologies for fibre size separation, fibre lofting and nose-only inhalation exposure. The target average fibre size was 20 μm long by 1 μm diameter.

Hamsters exposed to a kaolin RCF yielded a mesothelioma rate of 38%, but no lung cancers. There were no tumours among the chrysotile-exposed hamsters.

At the highest dose of 30 mg m−3 in rat studies, the commercial RCF all produced significant numbers of lung tumours, and some mesotheliomas. The fourth RCF, which had been heat-treated to simulate an after-service fibre, did not produce a significant excess of lung cancers, but did produce one mesothelioma.

A rat multi-dose experiment with three lower doses of the kaolin RCF yielded one mesothelioma among 379 rats, but no excess of lung tumours. The overall dose-response relation for lung cancer did not appear to be linear, consistent with the possibility of a threshold close to the Maximum Tolerated Dose.

No insulation wool (glass, stone or slag) exposure group had a lung tumour rate that differed statistically significantly from the tumour rate for the respective concurrent control groups, sham-exposed to filtered air. There was no significant difference in the total tumour rates between the four insulation wool groups and the control animals, and no significant dose-response relation above the respective sham-exposed control tumour rates.

The total lung tumour rates for rats in both chrysotile and crocidolite exposure groups were significantly raised. One animal in each asbestos-exposed group developed a mesothelioma, whereas no air control or insulation wool-exposed animal did so.”

“Six types of man-made fibers were administered intratracheally (2.0 mg/animal each a week, for 5 weeks; total 10 mg/animal) to female Syrian hamsters that were observed histologically for 2 years after administration. The fibers were rock wool [average diameter (D) = 6.1 μm, average length (L) = 296 μm], fiberglass (D = 0.65 μm, L = 16.8 μm), potassium titanate fiber (D = 0.36 μm, L = 7.17 μm), calcium sulfate fiber (D = 1.0 μm, L = 17.8 μm), basic magnesium sulfate fiber (D = 0.45 μm, L = 22.4 μm), and metaphosphate fiber (D = 2.38 μm, L = 64.1 μm). Tumors were observed in hamsters that had received basic magnesium sulfate fiber (9/20), metaphosphate fiber (6/20), calcium sulfate fiber (3/20), and fiberglass (2/20) but not in the control, rock wool, or potassium titanate fiber groups. The primary sites of the tumors were not only in the pleural cavity but also in the intracelial organs, kidney, adrenal gland, bladder, and uterus. Only a few of the tumors were identified as mesotheliomas by histological examination. In addition to neoplastic lesions, fibrosis, pleural thickening, and chronic inflammatory changes in the lungs were observed in the hamsters, but these changes appeared too mild to foster a pneumoconiosis such as asbestosis.”

“Fiber biopersistence as a major mechanism of fiber-induced pathogenicity was investigated. The lung biopersistence of 5 synthetic vitreous fibers (SVFs) and amosite asbestos was evaluated using the rat inhalation model. In contrast to several previous studies, this study examined fibers that dissolve relatively slowlyin vitroat pH 7.4. Fisher rats were exposed for 5 days by nose-only inhalation to refractory ceramic fiber (RCF1a), rock (stone) wool (MMVF21), 2 relatively durable special application fiber glasses (MMVF32 or MMVF33), HT stonewool (MMVF34), amosite asbestos, or filtered air. Lung burdens were analyzed during 1 year post-exposure. Fiber aerosols contained 150–230 fibers/cc longer than 20 μm (>20 μm). On post-exposure Day 1, long-fiber lung burdens for the 6 test fibers were similar (12–16 × 105fibers/lung >20 μm). After 1 year, the percentage of fibers >20 μm remaining in the lung was 0.04–10% for SVFs but 27% for amosite. Lung clearance weighted half-times (WT1/2) for fibers >20 μm were 6 days for MMVF34, 50–80 days for the other 4 SVFs, and >400 days for amosite. This study and 3 previous studies demonstrate a broad range of biopersistences for 19 different SVFs and 2 asbestos types. Ten of these fibers also have been (or are being) tested in chronic inhalation studies; in these studies, the very biopersistent fibers were carcinogenic (amosite, crocidolite, RCF1, MMVF32, and MMVF33), while the more rapidly clearing fibers were not (MMVF10, 11, 21, 22, and 34). These studies demonstrate the importance of biopersistence as an indicator of the potential pathogenicity of a wide range of fiber types.”

References C F Robinson, R. (1982). Mortality patterns of rock and slag mineral wool production workers: an epidemiological and environmental study. British Journal of Industrial Medicine, [online] 39(1), p.45. Available at: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1008926/ [Accessed 3 May. 2014]. Sciencedirect.com, (2014). Biopersistence of Synthetic Vitreous Fibers and Amosite Asbestos in the Rat Lung Following Inhalation. [online] Available at: http://www.sciencedirect.com/science/article/pii/S0041008X98984721 [Accessed 4 May. 2014]. Sciencedirect.com, (2014). Carcinogenicity of the insulation wools: Reassessment of the IARC evaluation. [online] Available at: http://www.sciencedirect.com/science/article/pii/027323009190048Z [Accessed 4 May. 2014]. Sciencedirect.com, (2014). Chronic inhalation studies of man-made vitreous fibres: Characterization of fibres in the exposure aerosol and lungs. [online] Available at: http://www.sciencedirect.com/science/article/pii/000348789400091E [Accessed 4 May. 2014]. Sciencedirect.com, (2014). Cytotoxic and oxidative effects induced by man-made vitreous fibers (MMVFs) in a human mesothelial cell line. [online] Available at: http://www.sciencedirect.com/science/article/pii/S0300483X04002677 [Accessed 4 May. 2014]. Sciencedirect.com, (2014). Cytotoxicity study of rock wool by cell magnetometric evaluation. [online] Available at: http://www.sciencedirect.com/science/article/pii/S0273230009001354 [Accessed 4 May. 2014]. Sciencedirect.com, (2014). Differential in vitro cellular response induced by exposure to synthetic vitreous fibers (SVFs) and asbestos crocidolite fibers. [online] Available at: http://www.sciencedirect.com/science/article/pii/S0014480005001231 [Accessed 4 May. 2014]. Sciencedirect.com, (2014). Fiber glass and rock/slag wool exposure of professional and do-it-yourself installers. [online] Available at: http://www.sciencedirect.com/science/article/pii/S0273230002000259 [Accessed 4 May. 2014]. Sciencedirect.com, (2014). Fiber glass exposure and human respiratory system cancer risk: Lack of evidence persists since 2001 IARC re-evaluation. [online] Available at: http://www.sciencedirect.com/science/article/pii/S0273230011000353 [Accessed 4 May. 2014]. Sciencedirect.com, (2014). Statistical analysis of results of carcinogenicity studies of synthetic vitreous fibres at Research and Consulting Company, Geneva. [online] Available at: http://www.sciencedirect.com/science/article/pii/000348789500054I [Accessed 4 May. 2014]. Sciencedirect.com, (2014). Tumorigenicity of fine man-made fibers after intratracheal administrations to hamsters. [online] Available at: http://www.sciencedirect.com/science/article/pii/S001393510580194X [Accessed 4 May. 2014]. Yuichiro Kudo, Y. (2009). Behavior of rock wool in lungs after exposure by nasal inhalation in rats. Environmental Health and Preventive Medicine, [online] 14(4), p.226. Available at: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2711883/ [Accessed 3 May. 2014]. Yuichiro Kudo, Y. (2009). Effects of rock wool on the lungs evaluated by magnetometry and biopersistence test. Journal of Occupational Medicine and Toxicology (London, England), [online] 4, p.5. Available at: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2670311/ [Accessed 3 May. 2014].