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9 questions and answers on chrysotile and health

Question 2

Is there evidence for a difference in potency of fibres according to fibre length?

Answer:

Two different sets of data are pertinent to this question:

1. There is evidence from experimental studies that while long (thin and durable) fibres are associated with ill-health effects in animals, no such association is found with asbestos fibres shorter than ~ 5 microns.
2. The great majority of fibres found in the general environment are shorter than 5 microns. Thus, while the presence of long fibres, such as may be found in the workplace, may be associated with ill-health effects in workers, the presence of short asbestos fibres in the general environment should not be of concern, at least for chrysotile asbestos.

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Question 3 >>

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References for Question 2:

Doll R, (1989). In Non-Occupational Exposure to Mineral Fibres, Eds. J. Bignon, J. Peto and R. Saracci. WHO/IARC Scientific Publications No. 90, Lyon: 511-518.

"Properly speaking, no particle should be described as a fibre unless it is at least 5 µm long and the diameter is less than one third of its length"

"There is increasing evidence that short fibres (properly described as elongated particles) are much less carcinogenic, if they are carcinogenic at all"

Davis JMG, Addison, J, Bolton RE, Donaldson K, Jones AD, and Smith T (1986). British Journal of Experimental Pathology 67(3): 415-430.

The effects of long vs short (100% shorter than 5µ) amosite fibres were compared. At the end of 12 months of dust inhalation (10 mg/m") long fibres caused development of widespread pulmonary fibrosis, and a third of the animals developed pulmonary tumours or mesotheliomas. No fibrosis at all, and no pulmonary neoplasms were found in animals treated with short fibre dust.

Chatfield EJ (1983). Short mineral fibres in airborne dust. Proceedings from a Symposium, Stockholm, September 28, 1982, Government of Sweden, Arbete och Halsa (publisher) 19: 9-93.

In rural areas the level of asbestos fibres longer than 5 microns are less than 1 fibre/litre (0.001 f/cc). In urban environments higher levels, up to 40 f/l (0.04 f/cc) were observed. Most fibres in general atmosphere are shorter than 5 microns (95-98%).

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