Abstract
The fibrogenicity and carcinogenicity of asbestos fibers are dependent on several fiber parameters including fiber dimensions. Based on the WHO (World Health Organization) definition, the current regulations focalise on long asbestos fibers (LAF) (Length: L ≥ 5 μm, Diameter: D < 3 μm and L/D ratio > 3). However air samples contain short asbestos fibers (SAF) (L < 5 μm). In a recent study we found that several air samples collected in buildings with asbestos containing materials (ACM) were composed only of SAF, sometimes in a concentration of ≥10 fibers.L−1. This exhaustive review focuses on available information from peer-review publications on the size-dependent pathogenetic effects of asbestos fibers reported in experimental in vivo and in vitro studies. In the literature, the findings that SAF are less pathogenic than LAF are based on experiments where a cut-off of 5 μm was generally made to differentiate short from long asbestos fibers. Nevertheless, the value of 5 μm as the limit for length is not based on scientific evidence, but is a limit for comparative analyses. From this review, it is clear that the pathogenicity of SAF cannot be completely ruled out, especially in high exposure situations. Therefore, the presence of SAF in air samples appears as an indicator of the degradation of ACM and inclusion of their systematic search should be considered in the regulation. Measurement of these fibers in air samples will then make it possible to identify pollution and anticipate health risk.
Highlights
Cumulative exposure to all fibers counted by transmission electron microscopy (TEM) was significantly associated with lung cancer risk, and to fibers of every length and diameter category when each dimension was considered separately
The lower effect of short asbestos fibers (SAF) in comparison with long asbestos fibers (LAF) is mostly founded on experimental studies as few epidemiological studies took short fibers into consideration
Based on literature data determining the role of fiber size in biological effects of asbestos fibers and on our present knowledge on their mechanism of action, it appears that the measurement of airborne asbestos concentrations limited to fibers with a length > 5 μm leaves out other types of fibers that may have health adverse effects
Summary
After a long latency period, asbestos exposure in humans is associated with severe diseases, including mesothelioma, lung cancer and fibrosis. Asbestos has been banned in several countries, many other countries still produce and/or use it. Epidemiological findings have depicted several waves of asbestos diseases. One may consider the first wave having occurred in miners, the second one in workers in the asbestos manufacturing industry, and the third wave among secondary occupations in buildings and constructions. Even in countries where asbestos was banned, workers and the general public can be exposed during incorrectly performed
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