Dr. THOMAS W. HESTERBERG, mestre em biologia pela UCLA, e tem doutorado em Toxicologia da UC Davis. MBA pela Universidade de Denver, USA.

1. Potential Health Risks from
Exposure to Chrysotile Asbestos
Dr. Thomas Hesterberg, PhD, MBA
Consultant in Toxicology
Littleton, Colorado USA
Federal Supreme Court of Brazil
Brasilia, Brazil
31 August 2012

2. Focus Should be on Potential
Health Risk of Chrysotile
• Health Risk = Potential Hazard X Exposure
• Most studies of chrysotile
focus on hazard
• In the 1500s, Paracelsus
knew that dose determines
the toxin
• If exposure kept low, there
is no risk
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3. Maintaining Low Chrysotile
Workplace Exposures
• Industry workplace limit of 0.1 fibers/cc
• Engineering controls in work areas
• Perform cutting in enclosed ventilated areas
• Maintain housekeeping with frequent cleaning
• Low exposure (< 0.1 f/cc) => No Health Risk
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4. Earlier Animal Inhalation
Studies of Chrysotile
• Lung cancer observed at very high exposures
– Exposures were > 1 million fibers/cc
– This is 10 million times industry exposure limit of 0.1 fiber/cc
• Lung clearance impaired due to overload
– Other non-toxic particles cause lung disease at these levels
(carbon black, talc and TiO2)
• These studies only showed effects of lung overload
• Remember: Risk = Hazard X Exposure
– Low exposures pose no risk to humans
Bernstein et al., Crit Rev. Tox., In Press, 2012.
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5. Inhalation Toxicity Study
of Brazilian Chrysotile
• Three month rat inhalation to Brazilian chrysotile
• Exposure to 536 WHO fiber/cc
– 5000 times the industry workplace limit of 0.1 fiber/cc
• No lung disease was observed at this level
• If no fibrosis at 90 days indicates no cancer in chronic study
ILSI, Inhalation Toxicology, 17:497–537, 2005
• A much higher exposure level produced only minimal fibrosis
• Risk is avoided if exposure is kept low
Bernstein et al., Inhal. Tox. 18 (5): 1–22, 2006.
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6. The Three Ds of Fiber Toxicology
Dose - Amount reaching the deep lung
Dimension - Thin fibers deposit in the deep lung; long
fibers are more toxic
Durability - Dissolution and breakage; more durable
fibers are more toxic
Hesterberg and Hart., Inhal. Tox., 2001
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7. Fiber Biopersistence in the Lung
Long Fiber (> 20 µm)
Incongruent Dissolution
Congruent Dissolution
Transverse Breakage
Complete Altered Biological
Dissolution Macrophage Reactivity
Uptake
Mucociliary Clearance
Intracellular Degradation
Hesterberg and Hart., Inhal. Tox., 2001
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8. Asbestos: Structure and Durability
Chrysotile
Amphibole
Bernstein and Hoskins, Reg. Tox. and
Pharm. 45: 252–264 , 2006.
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9. Inhalation Biopersistence Study Protocol

10. Biopersistence of Amosite and Chrysotile
Bernstein and Hoskins, Reg. Tox. and
Pharm. 45: 252–264 , 2006.

11. Inhalation Biopersistence Study
of Brazilian Chrysotile
• Chrysotile clearance half-time was 1.3 days
• Lower than man-made fibers in IARC Group 3
– Not classified as carcinogens
• Explains why no disease seen in animals
• And why no disease seen in humans
• Chrysotile can be used safely
Bernstein et al., Inhal. Tox. 18 (5): 1–22, 2006.
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12. Correlation of Results from
Biopersistence and Inhalation Toxicity
Biopersistence Inhalation Toxicity
Fiber Half-Life (Days) Fibrosis Tumors
Crocidolite 817 + +
Amosite 418 + +
MMVF32 79 + +
RCF1 55 + +
MMVF33 49 + -
MMVF21 67 + -
Not Classified as
MMVF10 (Fiber glass) 37 Carcinogen by IARC - -
MMVF 10.1 (Fiber glass) 14.5 - -
X607 9.8 Cancer Label not - -
MMVF11 (Fiber glass) 9 Required in EU - -
MMVF22 (Mineral wool) 9 - -
MMVF34 (Mineral wool) 6 - -
Chrysotile (Brazilian) 1.3 - -
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Hesterberg and Hart., Inhal. Tox., 2001

13. Potential Chrysotile Substitutes
International Agency for Research on Cancer (IARC)
• Examined chrysotile substitutes in 2005
• IARC did not indicate whether potential substitutes
would actually work in chrysotile applications
• Unlike chrysotile, most of the 13 substitutes had very
little toxicology information
• Little or no human studies on substitutes
• In Brazil, a combination of polypropylene and
cellulose fibers are proposed substitutes
WHO Workshop on Chrysotile
Substitutes, Lyon, France, 2005.
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14. Cellulose Fiber Health Effects
• Lung disease in rats and hamsters
• Biopersistent: clearance > 1000 days
– Compared to 1.3 days for chrysotile asbestos
• Excess lung cancer in paper mill workers
• Excess deaths from chronic obstructive pulmonary
disease and asthma in paper mill workers
• Not recommended as chrysotile substitute
National Toxicology Program, Toxicology
Report Series, No. 74, 2006.
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15. Polypropylene Fiber
Inhalation Toxicity
• Inhalation toxicity study of polypropylene fibers
• Exposures up to 48 fibers/cc
– Compared to 536 fibers/cc in chrysotile study
• Increase in reversible lung disease
• Levels of fibers in the lung increased with time
• Biopersistence: no lung clearance of fibers after 30 days
• Not recommended as a chrysotile substitute
Hesterberg et al., Fund. Appl. Tox.
19:358-366, 1992.
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16. Conclusions
• Chrysotile not toxic at non-overload levels
• Chrysotile clears from the lung within days
• Risk = Hazard X Exposure
• No risk identified below workplace limit (0.1 f/cc)
• Chrysotile substitutes not adequately tested
• Chrysotile can be used safely
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