Effects of electrostatic charge on the pathogenicity of chrysotile asbestos

Our plain-English summary of Effects of electrostatic charge on the pathogenicity of chrysotile asbestos, by J.M. Davis, R.E. Bolton, A.N. Douglas, et al (British Journal of Industrial Medicine, 1988).

The study

• Authors: J.M. Davis, R.E. Bolton, A.N. Douglas, A.D. Jones, T. Smith
• Journal: British Journal of Industrial Medicine
• Published: 1988;45(5):292-9
• Cited by: 18 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Two groups of 48 rats of the AF/HAN strain were exposed for one year to respirable dust clouds of UICC chrysotile asbestos at a dose level of 10 mg/m3. One group was treated with dust carrying the normal electrostatic charge produced during dust generation, whereas the other was exposed to dust discharged by exposure to ionising radiation from a thallium-204 source. After dusting most animals were retained for their full life span. At the end of the dusting period those animals treated with normally charged dust had significantly more chrysotile retained in their lungs than animals exposed to discharged dust. Subsequently, animals treated with normally charged dust developed more pulmonary fibrosis and more pulmonary tumours. These findings suggest that the charge carried by airborne fibres should be taken into account when considering the health risks from exposure to chrysotile. Highly charged fibres are more likely to be deposited in lung tissue and thus constitute a greater hazard.

In plain English

This was an animal experiment from the Institute of Occupational Medicine in Edinburgh. Two groups of 48 male rats breathed UICC chrysotile asbestos dust for seven hours a day, five days a week, for 224 days over 12 months. One group got dust with its normal electrostatic charge. The other got dust that had been passed by a radiation source to remove most of the charge. The median charge fell from 13 to 2 electrons per micrometre of fibre. At the end of dusting, rats given normally charged dust had about 20% more chrysotile retained in their lungs, a statistically significant difference. They also had more fibrosis around the small airways shortly after dusting (significant). Later lung scarring and lung tumour counts were also higher with charged dust, but these differences were not statistically significant. The authors concluded that highly charged fibres are more likely to be deposited in lung tissue and appear to produce more lung disease in proportion to the larger dust burden. They noted that with these group sizes some differences were not statistically significant.

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 inhalation experiment (rats) comparing electrostatically charged and discharged chrysotile dust, with most animals followed for their full life span
• Who was studied: Two groups of 48 male specific-pathogen-free (SPF) Wistar rats of the AF/HAN strain, 10 weeks old at the start of dusting, at the Institute of Occupational Medicine, Edinburgh, UK. Two batches of 36 and 25 undusted animals served as controls.
• Exposure: UICC chrysotile 'A' asbestos at a mean respirable mass concentration of 9.9 mg/m3 for both groups. Exposure was seven hours a day, five days a week, for 224 days over 12 months. One cloud carried its normal charge; the other was discharged by ionising radiation from a thallium-204 source. This cut the median charge from 13 to 2 electrons per micrometre of fibre length.
• Main results:
  • At the end of dusting, rats exposed to normally charged chrysotile had approximately 20% more chrysotile retained in their lungs than rats exposed to discharged chrysotile (p less than 0.01). The table reports means of four rats per group of 889 micrograms versus about 710 micrograms.
  • After dusting ended, clearance of chrysotile from the lungs was similar in both groups, with about 60% removed over six months.
  • At the end of dusting, the proportion of lung tissue with peribronchial fibrosis (scarring around the small airways) was higher in rats given normally charged dust than in rats given discharged dust (p less than 0.01).
  • In the oldest animals (13 rats given charged dust, 16 given discharged dust), the mean percentage of lung tissue with interstitial fibrosis was 12.2 for charged dust and 7.6 for discharged dust. Statistical analysis indicated this difference could have arisen by chance.
  • Lung tumours: rats given normally charged dust (36 rats) had 6 adenomas and 8 carcinomas. Rats given discharged dust (39 rats) had 4 adenomas, 6 carcinomas and 1 mesothelioma, listed in the table as a pleural mesothelioma. Tumour incidence did not differ significantly between the two groups.
  • Median survival was 28.8 months for rats given charged chrysotile and 29.5 months for rats given discharged chrysotile, not significantly different. Both control groups survived significantly longer (33.2 and 31.5 months, p less than 0.001).
  • There were no significant differences in tumours in organs other than the lung between the two chrysotile groups or the controls.
• The authors' conclusion: The authors concluded that highly charged fibres, if inhaled, are more likely to be deposited in lung tissue and appear to produce higher levels of lung disease in proportion to the increased lung dust burden. They also concluded that the charge on chrysotile fibres in the workplace should be considered.
• Limitations the authors state:
  • With the group sizes available, some of the differences (in fibrosis and tumours) were not statistically significant.
  • The charge on the fibres came from the dust dispenser and compressed air and was not under direct control. It was lower (about 13 electrons per micrometre) than the 20 reported in earlier short-term studies.
  • A sampler ran at too high a flow rate between days 160 and 200, so the charged dust cloud was slightly too low. This was corrected by raising that cloud's concentration over the last 24 days.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Chrysotile.

Medical terms in this study, explained in our Lexicon: Chrysotile, UICC, Pulmonary Fibrosis.

Related studies

• Inhalation and injection studies in rats using dust samples from chrysotile asbestos prepared by a wet dispersion process — J.M. Davis, J. Addison, et al. (1986)
• Kinetics of the bronchoalveolar leucocyte response in rats during exposure to equal airborne mass concentrations of quartz, chrysotile asbestos, or titanium dioxide — K. Donaldson, R.E. Bolton, et al. (1988)
• Pathogenicity of a special-purpose glass microfiber (E glass) relative to another glass microfiber and amosite asbestos — R.T. Cullen, A. Searl, et al. (2000)
• Adsorption of proteins by chrysotile and crocidolite: role of molecular weight and charge density — F. Valerio, D. Balducci, et al. (1987)
• Health in power stations — R.C. Browne (1971)
• Inhalation studies on the effects of tremolite and brucite dust in rats — J.M. Davis, J. Addison, et al. (1985)

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